© The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature 2025.The present paper presents a systematic approach to quantify the uncertainties when the piezoelectric shunt damping technique is employed to attenuate the vibration effect in arbitrary thin shell structure. The research used an experimental approach. The experimental apparatus employed in the present research was able to analyze the effectiveness of the piezoelectric vibration absorber when applied to a mechanical structure with arbitrary shape, typically used in automotive outer structures. The inherent variability typically found in an automotive body structure assembly and the tolerances of electronic circuits were taken into the account in the analysis. Then, the uncertainty propagation was studied in details for the mechanical structure, RL-shunt circuit, and piezoelectric vibration absorber working in the peak attenuation and in the frequency band. A large dispersion can be observed in the mechanical structure, with a variability of approximately 16 Hz for the natural frequency and 10 dB for the mobility peak amplitude. The piezoelectric capacitance had demonstrated discrepancies from 10 to 27%, in the experimental results. Finally, the experimental uncertainty propagation had demonstrated, when the piezoelectric shunt damping technique is employed, an overall average value of the peak attenuation of 6.25 dB, representing an effectiveness loss of approximately 32%, with a huge variability (standard deviation of 2.1 dB). Considering the frequency range of operation from 190 to 210 Hz, an attenuation of 2.2 dB was achieved in average, in an independent way from the mechanical structure resonant natural frequency.

© 2024 Elsevier LtdStructural members, such as stiffeners, are crucial in aeronautical structures, providing essential dynamic stiffness. However, variability introduced by manufacturing and assembly processes, as well as material inconsistencies, can lead to uncertainties in structural performance. It is crucial to incorporate these uncertainties into structural analysis to ensure reliable design. This paper utilizes the Stochastic Finite Element Method (SFEM) to address uncertainties in typical structural members used in aeronautics. The Perturbation Technique, based on Taylor series expansions, was employed to model uncertainties in aircraft stiffeners. The study focuses on natural frequencies and modal analysis to evaluate the impact of uncertainties on beams with hat and Z sections, commonly used as stiffeners in aircraft panels. These stiffeners were modeled using the Timoshenko beam theory, and sensitivity analysis was performed to identify key contributors to variability. The perturbation parameter was validated through Monte Carlo simulations. Sensitivity analysis, employing gradient-based methods, identified significant factors affecting variability in natural frequencies. A different perturbation parameter was necessary based on the stiffener's geometry: thickness variations required a perturbation parameter on the order of 10−3, whereas dimensions changes in the flange and height required parameters on the order of 10−2. These results underscore the importance of choosing appropriate perturbation magnitudes to avoid inaccuracies in the deterministic frequency response. Once a perturbation parameter is established, it can be applied to similar regions, ensuring the robustness of the SFEM methodology in analyzing the dynamic response of aeronautical structural reinforcements.

© 2024, Academia Brasileira de Ciencias. All rights reserved.The transmission gearbox of military helicopters, such as the H225M, experiences intense dynamic loads, leading to the detachment of ferromagnetic particles, often due to wear or fatigue. This poses safety risks, as excessive particle detachment demands stringent maintenance. To address this, the study applies machine learning algorithms to predict particle detachment using data from the Flight Data Recorder and Health and Usage Monitoring System. The approach aims to mitigate operational challenges faced by the Brazilian H225M fleet while considering aviation safety criteria and the pre-processing needs for an effective machine learning application.

© CSP - Cambridge, UK; I&S - Florida, USA, 2024In this work, the influence of magneto-rheological fluid embedded on journal bearings in the dynamic behavior of rotors is considered. The modified Reynolds equations for Bingham viscoplastic materials are used for calculation of the nonlinear hydrodynamic forces. Flexible rotors are modeled by the finite element method. The static weight of the rotor, unbalance and bearing hydrodynamic forces are included in the equations of motion. Non-linear hydrodynamic forces calculation depends on the relative positions of the journal bearings. The dynamic system response is computed by the Newmark method modified to obtain the calculation of the differential displacements and velocities for each time step. By incorporating the Newton-Raphson method the necessary corrections are included in the equations of motion. Time and frequency responses are presented for two of the case studies. The sudden elevation in oscillation magnitudes due to the oil whip phenomenon is not observed in the run-up test after the application of electromagnetic induction on the MR fluid. Furthermore, the controlled variation in the viscosity of the MR fluid causes significant changes in the bearing movements, as demonstrated by the orbit graphs.

© Published under licence by IOP Publishing Ltd.This research performs a nonlinear analysis of a typical section airfoil limited to two degrees of freedom emphasizing the evaluation of the effects of a quartic structural stiffness on dynamic responses. Analytical studies are presented based on a simulated model. First, the influence of the quartic term of nonlinear structural stiffness in spring moment is evaluated. Then, phase portraits are presented as a function of freestream velocity, and a time domain decomposition of time histories is performed to identify the limit cycle frequency. Additionally, it maps the region of limit cycle oscillations (LCOs). Furthermore, the aim of this work is to characterize the nonlinear aeroelastic response.

© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2024.The vibration energy collectors based on piezoelectric resonators are promising elements for energizing remotely located systems. However, differences between the resonant frequency of these traditional harvesters and the vibration frequency can drastically decrease the collected energy and make them ineffective. Appropriate mathematical models, different analyses, and optimization techniques to tune the resonant frequency of piezoelectric collectors have been researched. In this study, the model of an inverted vertical cantilever beam with a piezoelectric patch and a tip mass is used for energy harvesting. The beam is subjected to base excitations that can induce large lateral displacements of the tip, and consequently large deformation for the piezoelectric patch. Applying the homotopy analysis method (HAM) to the coupled electromechanical governing equations of motion, novel analytical solutions of the transverse displacement of the cantilever beam, its amplitude and phase as well as the output voltage obtained from the piezoelectric patch are derived. The analytical solutions are derived for the transversal displacements of the beam, even if it presents a varying cross-sectional area. The analytical solution considers the nonlinear behavior characteristics emphasizing the capabilities of a first-order approximation of HAM to present highly accurate closed-form solutions. The accuracy of this approximation of HAM is confirmed by comparison to numerical integration methods.

© 2020, Krishtel eMaging Solutions Private Limited.Background: The quasi-3D finite element model includes the smart actuation on a three-layer sandwich plate with laminated composite face-sheets. In the model, the face-sheets are represented as Reissner-Mindlin plates and the core is modeled as a three-dimensional continuum. Purpose: This representation allows accurate modeling for a wide range of core types. In this model, the electrical constitutive relations of piezoelectric layers are included in the formulation of the face-sheets. In previous publications, this quasi-3D finite element formulation has demonstrated some advantages in comparison with solid finite element models. The aspect ratio of three-dimensional elements can make it rather inconvenient to use on very thin faces-sheets, which makes the number of degrees of freedom very high. Methods: Analytical through-thickness integration of the energy expressions is used to reduce the three-dimensional problem to two dimensions for the evaluation of mass and stiffness matrices. In the same way, the analytical integration of the electrical voltages work applied to the piezoelectric layers produces the piezoelectric actuation force vector. Result: This research assesses the accuracy of the proposed model for dynamic responses of sandwich plates using a broad range of core-to-face-sheet stiffness ratio. Conclusions: The numerical results show that deflections promoted by the voltage applied to piezoelectric layers of the sandwich plate are very small, even if the core is very flexible. The results also indicate that the core flexibility strongly affects the natural frequencies of the higher bending modes.

© 2025 The Author(s)Assessing the bending response of infiltrated reinforcement fabrics is crucial in wet compression molding (WCM) as it affects macroscopic wrinkling. Binder-stabilized fabrics may be used in WCM to improve handleability and reduce defects, necessitating their characterization. This study examines the bending behavior of an infiltrated binder-stabilized carbon fiber unidirectional non-crimp fabric (UD-NCF), focusing on the effects of viscosity, loading rate, and binder pre-activation. Infiltration reduces bending stiffness compared to dry fabric owing to lubrication and lower tow-stitch friction, while higher loading rates increase bending stiffness for all considered conditions. Moreover, binder pre-activation increases fabric stiffness by enhancing tow-stitch cohesion and friction. As the first investigation on infiltrated binder-stabilized UD-NCF bending, this work advances understanding of the complex bending response.

© The Author(s), under exclusive licence to Springer-Verlag London Ltd., part of Springer Nature 2025.A device apparatus was designed and built to enable the testing of sheet metal undergoing cyclic forward and reverse tension–compression loads under plastic deformation, while preventing the specimen from buckling. This test allows the identification of parameters for the characterization of the material according to advanced hardening models, that are of utmost interest to the automotive industry, for accurate representation of the physical phenomena occurring during mechanical forming, which enables for tighter manufacturing tolerances. The test specimens were manufactured from steel sheets made of materials BH220 and DP600, with thicknesses of 0.65 mm and 1.00 mm respectively. For each specimen tested, three tension–compression cycles were performed, at a strain rate of 0.5 mm/min. The maximum displacements were 0.6 mm in tension and 0.6 mm in compression. A fork configuration was used in which the device has four main plate blocks to transmit the longitudinal displacement of the machine to the sheet metal and to restrict the plane transverse displacement. The results show that the device is capable of creating the cyclic stress–strain curve of which accurate parameters of Yoshida-Uemori model can be extracted.

© 2024Identifying the occurrence of gear contact fatigue failure as early as possible is essential for condition-based maintenance (CBM). Vibration signals can be used to identify gear contact fatigue. However, the use of vibration signals can be challenging due to its complexity, compounded by lower levels of vibration during the initial stages of contact fatigue. The present study details a new algorithm that integrates stand-alone features to correlate the vibrational signal with early failure occurrence. The study aim is to identify the failure in the early stages, before reaching the ISO 6336–5 stopping criterion of 4 % damaged area. A damage induction on the flank of helical gears is applied to simulate and characterize the failure occurrence. Damping characteristics with impact evaluation, Kurtosis analysis and the monitoring of the Gear Meshing Frequency are applied to characterize the failure signature. This strategy stands out by the integration of these stand-alone features and their behavior. The algorithm's capacity is verified through durability tests, promoting the natural evolution of this failure mode. Results show a success rate of above 80 % at identifying the failure presence before the stopping criterion limit.

© 2024 Elsevier LtdA composite beam finite element is designed to capture through-thickness effects, specifically normal stress and strain and transverse shear, in the context of geometrically nonlinear analyses. The starting point for the formulation is a similar element already proposed for linear analyzes based on a global–local superposition approach, where local functions are defined in each layer of the laminate, and global functions are defined along the thickness. The consistency of the kinematic hypotheses is guaranteed by imposing the continuity equations of displacements through the thickness, the force balance equations along the thickness, directly or indirectly, by imposing the continuity of transverse stresses, and by applying the boundary conditions on the lower and upper surfaces of the elements. In the context of nonlinear analyzes, the imposition of continuity of displacements is straightforward. However, the continuity of the transverse stresses needs to be carefully imposed, as the relevant stresses are the second order Piola-Kirchhoff stresses and the strains are the Green-Lagrange strains, consistent with the total Lagrangian approach used. The constitutive equations are written in incremental form and a detailed analysis is conducted to ensure that the stresses and strains involved are physically consistent across the different reference frames employed. In order to assess the accuracy of the numerical model implemented, a unique semi-analytical technique is developed to obtain the response of asymmetrical laminated beams under compression.

© 2024 Elsevier Inc.The present manuscript delineates the derivation of strong solutions for the linear elasticity problem in a two dimensional rectangular beam. The materials under consideration can exhibit either isotropic or orthotropic properties. Additionally, the analysis is not restricted to slender beams because the ratio between the length and the height of the beam can be arbitrary. The boundary conditions fall into the Dirichlet category, implying that both horizontal and vertical displacements are specified on all four surfaces. The sole requirement is that these surface displacements are continuous functions, although they may not necessarily be smooth. Since the displacements at the surfaces can be arbitrary, there is no need to consider approximations, such as those concerning local (small) boundaries in slender beams. Nonetheless, it is demonstrated that an equivalent principle to the Saint-Venant principle exists for pure displacement boundary conditions. The partial differential equations are solved through the separation of variables method, leading to the identification of two solution types, encompassing both cosine and sine Fourier series. Particular emphasis is placed on evaluating the convergence of these solutions. For two distinct and general examples, it is confirmed that the solutions indeed exist.

© 2024 The Authors. Published by Elsevier B.V.Additive Manufacturing (AM) is vital for industrial innovation, offering high potential for groundbreaking solutions. However, its successful implementation still depends on overcoming several challenges. Particularly, the assessment of surface integrity in AM-generated components, and its degradation when subjected to contact stresses presents an ongoing endeavor. Within this context, the current work delves into the study of the surface integrity of 20MnCr5 case-hardened samples manufactured through laser powder bed fusion (L-PBF), as well as delves into the investigation of surface failure progression when the samples are subjected to cyclic contact stresses. This study encompasses the analysis of residual stresses, hardness, and roughness of specimens manufactured through both additive and conventional production routes. The study's findings show that it is feasible to attain analogous surface quality when proper finishing is applied to L-PBF samples. Although, despite the comparable surface quality, the contact fatigue performance was significative lower on the AM sample when compared to the conventionally manufactured. Additionally, additive manufacturing brings up new challenges to performance by presenting a heterogeneous stress distribution and sub-superficial porosity. In conclusion, to attain a desirable surface integrity for additive manufactured parts, further research should not only focus on improving the process parametrization but should also developing finishing routes especially oriented to additive manufacturing, considering therefore how the interaction between the manufacturing processes will evolve into a desirable surface integrity state.

© 2023 Elsevier B.V.The current study proposes a shot peening model which enables the residual stress interaction with grinding, a typical combination for gear finishing. The effect of the interaction on the stress state development was addressed by comparing the residual stress state from a standalone shot peening procedure, against the residual stress state arising from a manufacturing route where the interaction of shot peening and grinding takes place. In the interaction model, the grinding procedure generates a pre-loaded condition on the material, modifying the internal strain system of the gear tooth. This pre-loaded system, when disturbed by shot peening, reaches a new internal strain equilibrium. In the interaction model, a 24% less compressive stress state was attained when compared with the standalone shot peening process. A significant shift in the depth and magnitude of the peak compressive stress was also observed. On account of the numerical study of the processes’ interaction, the developed model substantially contributed to understanding the residual stress formation during manufacturing chains.

© 2023, The Author(s), under exclusive licence to The Brazilian Society of Mechanical Sciences and Engineering.This work employs a micromechanical theory and kinematic relationships to describe the displacement field in individual unidirectional composite plies. The technique relies on an incremental approach where the misalignment angle of fibers is the main variable in the analysis. Upon convergence at a certain loading level, stresses and strains are evaluated in the fibers and matrix using micromechanics, and a specific failure criterion is applied. The Ramberg–Osgood relations are used to correct degraded mechanical properties of the resin in the nonlinear regime. The use of a 2D finite element model with a 3° initial misalignment angle of fibers, showed a good approach to complement the problem solution. The Hashin-Rotem failure criterion and experimental data obtained by Matsuo (Compos Part A: Appl Sci Manuf, 93:117-125, 2017) are used to validate the technique. It is observed that the numerical and experimental results obtained correlate well.

© 2022 Elsevier Masson SASDue to the unique characteristics of composite materials, the study of composite beams is far more complex than the study of homogeneous beams. The finite element method has proven to be a powerful approach to analyze composites subjected to the most distinctive situations. In the present work, two element solutions using cubic polynomials are considered: with continuous stresses and with discontinuous stresses along the transverse direction. Both converge to the analytical solution as the number of elements increase, i.e. with a finer mesh. Besides satisfying the boundary conditions at the surfaces and interfaces, the first solution gives better outcomes close to the center of the beam. On the other hand, the second solution gives better outcomes close to the borders of the beam, but it has a larger number of nodal parameters. The results are compared to a zig-zag element solution which has a number of nodal parameters independent of the number of layers. An element based on the Reissner mixed variational theorem is also included for additional comparisons. It is concluded that the cubic polynomials used to expand the cross section functions, must be different in each layer in order to achieve a reasonable agreement between the analytical and the calculated transverse normal stress.

© 2023 IEEE.The paper describes the constitution of the Engineering Research Center for the Aerial Mobility of the Future (ERC-AMF) having ITA as the host institution, Embraer as the industrial partner, and researchers from the University of São Paulo and the University of Campinas. The objective of the ERC-AMF is the realization of R&D to contribute to overcoming challenges to the shaping of aerial mobility in the upcoming decades. These challenges arise from the necessity of reducing pollutant and noise emissions, and the need for increased efficiency of manufacturing processes, besides the trend of introducing in the market novel aircraft adapted for operation in urban environments and short-range travels. Five research areas are focused on the first operation phase of the Center: Machine Control for Electric Propulsion; Aeropropulsion Integration in Electric Aircraft; Methods for Decision Making in Autonomous Systems; Advanced Design for Metallic Additive Manufacturing; and Intelligent Aircraft Final Assembly. Each line will be developed by researchers from partner universities and engineers from Embraer. It is expected that the Center will contribute to the appropriation, by the Brazilian aeronautical industry, of scientific and technological knowledge generated, and, as a result, increase its preparedness to face challenges that shall be overcome in the process of shaping the aerial mobility of the upcoming decades.

© 2022, The Author(s), under exclusive licence to The Brazilian Society of Mechanical Sciences and Engineering.This two-paper series proposes a unified theory that gives rise to a family of quasi-3D composite elements. The first paper presents the element formulation and its basic capabilities: the ability to capture transverse normal (σz) and shear (τyz, τxz) stresses, suitability for thermoelastic analyses and compliance to both displacements and transverse stress continuity requirements. These capabilities are inherent to the element since a global–local superposition approach is devised that, from inception, guarantees that equilibrium equations, continuity consistency and boundary conditions are fully met. A simple validation analysis was conducted in part I that initially pointed to a very promising direction with high numerical efficiency of the element. This second paper investigates the element numerical performance under different scenarios: use of three- and four-node parent elements, degree of global interpolation functions, adequacy of different local interpolation functions (F0, F1, G0, G1, H0, H1) and consideration of a more practical configuration of a reinforced panel consisting of multiple laminates. Through-the-thickness displacements, strains and stresses are obtained and shown to be of reasonable accuracy. Results are compared against a highly refined mesh of 3D brick elements implemented in a commercial software that provide a benchmark for the elements capabilities.

© 2022, The Author(s), under exclusive licence to The Brazilian Society of Mechanical Sciences and Engineering.In a series of two papers, a unified formulation for new plate composite elements is proposed that captures through-the-thickness effects, specifically normal and transverse shear stresses and strains. Thermal effects are also considered, including thermal effects through-the-thickness. This first paper is devoted to the fundamentals of the proposed unified formulation. The elements proposed are displacement based and the number of degrees of freedom is kept as small as possible, all of them possessing clear physical meaning. The elements are built using local functions defined at each layer and global functions defined along the thickness. The consistency of the kinematic assumptions is guaranteed through the imposition of displacement continuity along the thickness direction, transverse stress continuity and boundary conditions at the bottom and top surfaces of the elements. The formulations are developed for either isotropic or orthotropic materials. The formulations shall prove substantially more efficient than those based on solid elements traditionally used to capture normal transverse stresses. In the sequel, a second paper presents a variety of numerical results obtained using the proposed formulation and discusses its capabilities and potential.

© 2022, The Author(s), under exclusive licence to Springer-Verlag GmbH Austria, part of Springer Nature.Composite materials present challenging gaps to be studied due to their unique characteristics. The finite element method has been used to analyze composite materials subjected to the most distinctive situations. In the present work, the advantages of three element solutions studied previously are combined to develop a fourth element solution. First, decreasing the degree of the polynomials representing the axial displacement at the bottom and at the top surfaces circumvents shear locking in beams. Second, including the homogeneous solution ensures the continuity of the displacements between elements, but in this case the determination of the stiffness matrix requires a huge amount of computational time. However, it is shown that only modifications close to the original block diagonal matrix need to be considered, since far from the diagonal the contribution of the homogeneous solution is negligible. Additionally, a procedure is described to calculate a more accurate value for the stress σz.

© 2022 Elsevier Masson SASThe use of composite materials in several sectors has been gaining distinction in recent years. However, due to their high costs, as well as unique characteristics, they present challenging gaps to be studied. The finite element method has been used as a way to analyze composite materials subjected to the most distinctive situations. Three element solutions are compared, which can be applied to composite beams. The accuracy of the outcomes does not improve with higher degree polynomials, but the inclusion of the homogeneous solution to solve a system of differential equations results in a better outcome when considering the normal strains. Special attention is paid to the continuity of the displacements between adjacent elements. Finally, it is explained why the calculated axial normal stress looks much better than the transverse normal stress.

© 2021The determination of the fatigue behavior at a component level usually requires dedicated test rigs and an expressive amount of time. The hours spent on such machinery are expensive; therefore, solutions to reduce experimentation time are most welcomed. In this context, this investigation aims at developing a procedure for rapid determination of the fatigue strength of crankshafts by means of a thermographic methodology. The use of infrared cameras for fatigue strength analysis was first assessed in standard dog-bone specimens. Crankshafts were then tested in an in-house fatigue test rig using the conventional staircase method and the thermographic method. Sample batches with different manufacturing parameters were produced and tested to assess the robustness of the proposed alternative technique. Results of the dog-bone test campaign revealed a good correlation between fatigue strength estimates obtained with the conventional Wöhler curve and the thermographic methodology. Finally, the thermographic technique also delivered results in close agreement with the staircase method for all crankshaft batches. The proposed procedure was found to be a viable, rapid alternative to conventional fatigue test programs, with potential application for complex structural components such as crankshafts, among others.

© (2022) by International Council of Aeronautical Sciences (ICAS) All rights reserved.This work employs a micromechanical theory and kinematic relationships to describe the displacement field in individual unidirectional composite plies. The technique relies on an incremental approach where the misalignment angle of fibers is the main variable in the analysis. Upon convergence at a certain loading level, stresses and strains are evaluated in the fibers and matrix using micromechanics, and a specific failure criterion is applied. The Ramberg-Osgood relations are used to correct degraded mechanical properties of the resin in the nonlinear regime. The Hashin-Rotem failure criterion and experimental data obtained in the literature are used to validate the technique. It is observed that the numerical and experimental results obtained correlate well.

© 2025, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.This study investigates the feasibility of hybrid-electric propulsion for regional aircraft operating in Brazil, using real-world data from Azul Conecta, a subsidiary of Azul Brazilian Airlines. The analysis supports the company’s decision to acquire retrofit hybridization kits from Ampaire by providing technical, operational, and sustainability assessments tailored to its route network. A validated performance model of the Cessna Grand Caravan EX was integrated into the FAST-OAD-CS23HE framework to simulate different mission lengths and hybridization levels. To properly capture the economic impact of environmental gains, this work introduces the Sustainable Direct Operating Cost (DOCSA), a novel metric that accounts for monetized carbon credits in the total cost evaluation. Under this framework, propulsion alternatives are assessed not only by their raw DOC, but also by their effective cost after environmental externalities are internalized. For example, at a 500-nm mission with a 450-kWhybrid configuration, the conventional DOC is reduced by approximately 1.2%, while the SA-DOC shows a reduction of 11.9% when carbon credit revenues are considered. The use of Sustainable Aviation Fuel (SAF) demonstrated the highest decarbonization potential, achieving up to 71% CO2 reduction without any payload penalty. The findings contribute to both strategic fleet planning and the development of public policies to incentivize low-emission aviation through carbon market integration.

© 2024, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.This work proposes an assessment of the delta wing sweep variation of a Generic Future Fighter in the conceptual design phase. Combat aircraft have critical control and therefore the stability analysis of these configurations is compared. Little variation in stability was observed between the 5 different configurations. This indicates that other requirements may become more relevant when designing a fighter aircraft, such as stealth and performance. Thus, this work aims to evaluate the impact of wing sweep on the longitudinal stability of fighter aircraft, considering five different sweep angles: 45°, 47°, 50°, 55°, and 60°. To conduct this analysis, a numerical evaluation, using the Vortex Lattice Method (VLM), wind tunnel results and parameter identification data from past work will be used to obtain the aerodynamic data for each configuration. The aerodynamic data will then be used in a time-domain flight simulation model to analyze the longitudinal stability of the aircraft.

© 2024, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.The upward variation in altitude implies a decrease in air density. This phenomenon induces modifications in the aerodynamic forces and moments exerted on an aircraft, especially in combat aircraft. Such alterations have profound implications on the stability and controllability of the aircraft, thereby necessitating the implementation of distinct control strategies contingent upon the altitude. Conventional control systems, which are typically calibrated for a pre-defined set of environmental conditions, may not exhibit optimal performance throughout the entire range of operational altitudes encompassed within the flight envelope. This research work analyzes the Generic Future Fighter (GFF) subscale model and has as its central proposition the use of Linear Matrix Inequalities (LMIs) in the design of a Stability Enhancement System (SAS) for the aircraft, the in order to guarantee stability and maintain performance at different operating altitudes. The results obtained from the simulation showed that the open-loop response presents significant variations in the dynamic behavior of the aircraft with changes in altitude. Using LMIs, the designed controller effectively adjusted the feedback gain matrix, ensuring performance under different flight conditions, and the closed-loop response demonstrated that the control system maintained a similar operating condition regardless of altitude.

© 2024, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.This manuscript discusses the impacts of two factors on the results of a non-viscous CFD simulation of a combat aircraft: mesh refinement and the leading-edge sweep angle. Unlike viscous simulations, the non-viscous simulation of a delta wing with a rounded leading edge has a unique characteristic where mesh refinement consistently alters the flow topology, making mesh independence analysis ambiguous. To investigate this phenomenon further, the Generic Future Fighter, an aircraft initially devised by Linköping University and further studied in conjunction with Instituto Tecnológico de Aeronáutica, was used to validate this issue through aerodynamic coefficients obtained from wind tunnel tests from another work. Subsequently, using the mesh that yielded the most accurate results, the leading-edge sweep angle was varied while keeping the rest of the aircraft and other wing geometric parameters constant. The results of the first phase confirmed that mesh refinement progressively delays the separation of the leading-edge vortex. The results of the second phase were inconclusive, highlighting several points that require further investigation. The manuscript also presents a discussion on the highly nonlinear interaction between the canard vortex and the wing vortex, as well as the effect of the mesh on these interactions, an aspect lacking in recent studies which typically consider only a single lifting surface.

© 2024, Academia Brasileira de Ciencias. All rights reserved.Multirotors Aerial Vehicles are special class of Unmanned Aerial Vehicles with many practical applications. The growing demand for this class of aircraft requires tools that speed up their development. Simulated environments have gained increasing importance, as they facilitate testing and prototyping solutions, where virtual environments allow real-time interaction with simulated models, with similar behavior to real systems. More recently, the use of Augmented Reality has allowed an increasing experience of immersion and integration between the virtual world and a real scenario. This work proposes the use of Augmented Reality technology and a simulated model of a multirotor to create an interactive flight environment, aiming to improve the user experience in the analysis of simulated models. For this purpose, a smartphone was adopted as a hardware platform, a game engine is used as a basis for the development of the Augmented Reality application, that represents a numerical simulation of the flight dynamics and the control system of a multirotor, and a game controller is adopted for user interaction. The resulting system demonstrates that Augmented Reality is a viable technology that can be used to increase the possibilities of evaluating simulated systems.

© 2023, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.Thicker blunt trailing edge airfoils are extensively employed in many applications, especially in wind turbines. Their structural properties, such as strength section and area moment of inertia, and aerodynamic characteristics, such as higher curve slope and maximum lift coefficient, are particularly specials to design a blade that operates under varying cyclic loads and speeds, which establish dynamic conditions of creep loading, and fatigue stress. The main disadvantages are the higher drag and an intense and broadband noise, caused by the vortex shedding downstream. Many improvements have been achieved using passive flow controls to mitigate those problems, but there is still wide design space for better solutions. In this sense, the aim of this study is to investigate the potential of waviness applied on truncated trailing edge of thick airfoils as a possible efficient flow control mechanism. For this purpose, experiments in wind tunnel is carried out in order to understand the effects of different wavy geometries on truncated airfoil. A NACA 0020 airfoil is selected as a baseline profile, truncated at 15% from the trailing edge, and three configurations of waviness are tested: A = 0.11c, λ = 0.40c; A = 0.03c, λ = 0.40c; and A = 0.03c, λ = 0.11c. The phenomena is evaluated measuring forces in a wind tunnel at a Reynolds numbers of 200,000, and applying a technique of oil flow visualization. Main results shows that the wavy model presents much higher values of aerodynamic efficiency for lower angles of attack up to α = 5º. Besides that, another wavy configuration overcame the efficiency of the smooth truncated model for almost all pre and pos-stall regions. For low angles, a possible explanation is the break of vortex shedding coherence spanwise in the base, while for higher angles waviness allows to avoid flow separation over the surface.

© 2023, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.Recently, waviness applied on leading edge of airfoils has been extensively researched. As a biomimetic solution, the also called tubercle has brought up many insights on passive flow control mechanisms and inspired other studies. Therefore, the present study aims to investigate the potential of waviness now applied on the trailing edge of airfoils. For this purpose, experimental tests in wind tunnel is carried out in order to understand the effects of different wavy geometries on the flow. A NACA 0020 airfoil is selected as a baseline profile and three configurations of waviness are tested: A = 0.11c, λ = 0.40c; A = 0.03c, λ = 0.40c; and A = 0.03c, λ = 0.11c. The phenomena are evaluated measuring forces at a single Reynolds numbers of 250,000, and correlating it with a flow topology analysis provided by an oil flow visualization technique. Main results show that the wavy model with parameters A = 0.11c, λ = 0.40c presents the best aerodynamic efficiency, with similar lift values compared to the baseline profile, but with reduced drag coefficients, also briefly delaying stall separation. Flow visualization shows that this case has larger regions of attached flow.

© 2025 The Author(s)At the heart of electrocatalyst design and development lies the concept of active sites that are usually identified as those sites for adsorption where the conversion of interest occurs. However, electrochemical interfaces are complex systems where the exact structure and dynamics of interfacial species during a reaction greatly depend on the local reactive microenvironment, including co-adsorbates and solvent molecules, that may include structural transformations upon adsorption, the charge-transfer dynamics, and/or the x,y charge-induced electric field distribution. We review the concept of active sites in electrocatalysis within these lines in light of recent studies that point out the necessity to expand the still widely spread idea of quasi-static atomic-scale sites toward the picture of a dynamically reactive microenvironment: the active site can extend over several tens on nanometers due to surface structural transformations during the reaction, includes interdependent components such as electrode and electrolyte as well as target reactant geometric and electronic structures, and often spontaneously rearranges during the electrocatalytic reaction. Thus, to define optimal reactions conditions, the reactive microenvironment as a whole needs to be considered.

© 2023 Elsevier B.V.The interaction of single Fe, Co, Ni, and Cu atoms with polar terminations of orthorhombic Mo2C(0 0 1) surface has been investigated at low surface coverage by using density functional theory. Calculations indicate high stability of all considered adsorbates, regardless the surface termination. The presence of a single foreign atom has a localized impact on the properties of the surface, causing charge redistribution in the adsorbate/surface interface. As the result lowering of the work function is observed for both Mo2C(0 0 1) terminations. Another effect is shifting the position of d-band center further away from the Fermi level for surface Mo atoms of metal-terminated carbide, while no changes are seen for carbon's near-Fermi level electronic states in the case of C-terminated modified surface. Results demonstrate a short-range effect on the stability of atomic hydrogen caused by the foreign adatom on both terminations. Specifically, the observed adsorption energy weakening would entail an enhancement in the catalytic activity of Mo2C toward hydrogen evolution reaction according to the Sabatier principle. Results evidence that molybdenum carbide modified by cobalt and iron is expected to be more active toward hydrogen evolution reaction than Mo2C modified by nickel and copper or than unmodified carbide.

© 2022 American Chemical Society. All rights reserved.Shell-isolated nanoparticles (SHINs) with a 37 nm gold core and an 11 nm tin dioxide (SnO2) coating exhibited long-life Raman enhancement for 3 months and a wide pH stability of pH 2-13 in comparison with conventional SiO2-coated SHINs. Herein, Au-SnO2is demonstrated as a more durable SHIN for use in the technique Shell-Isolated Nanoparticles for Enhanced Raman Spectroscopy (SHINERS).

© 2022 American Chemical Society. All rights reserved.Theoretical insights have been gained into nickel adatom interaction with model platinum basal planes, and evolution of their fundamental properties with growing nickel surface coverage has been analyzed. Calculations have been performed using density functional theory with the Perdew-Burke-Ernzerhof exchange correlation functional and dipole corrections. The presence of a single Ni atom appreciably affects the Pt surface, lowering the work function and shifting the d-band center position away from the Fermi level of Pt atoms in contact with Ni. At increasing coverage, Ni bonding strength with Pt increases and plain structures are formed on all considered surfaces, although the initial tendencies, seen for the Pt fundamental properties upon Ni adsorption, do not change. Compared to reported experimental data, results suggest that lowering of the work function, φ, of Pt(111) upon Ni adsorption may facilitate charge transfer through the electric double layer, improving the rate of the hydrogen evolution reaction in alkaline media on Ni-modified Pt(111) surfaces. Hence, this rate-promoting effect would be expected to be lower for Pt(110) and (100) because of the lower impact of Ni adatoms on φ for these two surfaces. Results of the present study improve the current understanding of adatoms' electronic effects on the substrate and contribute to the scientific basis for the systematic design and development of Pt-based catalysts.

© The Author(s) 2025.The reuse of powder in laser powder bed fusion offers a promising approach to optimizing material usage, reducing costs, and improving sustainability. However, its application in the aeronautical sector presents significant challenges due to strict certification requirements, process reliability concerns, and the need to maintain mechanical integrity over multiple reuse cycles. This study conducts a comprehensive and global analysis of powder reuse, considering its mechanical, economic, and environmental impacts. The methodology includes powder characterization, mechanical testing, cost modelling, and environmental life-cycle assessment, providing a holistic understanding of powder degradation and its implications. Results confirm that successive reuse cycles lead to minor changes in powder morphology and an increase in oxygen content, yet mechanical properties remain within acceptable limits, with a slight improvement in tensile strength. Economically, powder reuse significantly reduces costs, with a 33% decrease observed after a single reuse cycle and further reductions in subsequent cycles. Environmentally, the life-cycle assessment highlights substantial benefits, including a dramatic reduction in material waste, energy consumption, and carbon footprint, reinforcing the sustainability advantages of controlled powder reuse. These findings validate the feasibility of powder reuse in industrial-scale additive manufacturing. The study highlights the importance of implementing standardized reuse protocols to ensure consistency in mechanical properties, minimize variations in powder characteristics, and maintain process stability over multiple reuse cycles. Additionally, it underscores the need for further research into long-term powder recycling strategies, including controlled rejuvenation methods, advanced monitoring techniques, and predictive models for powder degradation. By optimizing reuse practices, industries can maximize cost savings, enhance material sustainability, and significantly reduce the environmental impact of additive manufacturing processes, reinforcing the viability of AM as a competitive and responsible manufacturing approach.

© The Author(s) 2025.Additive manufacturing is nowadays an alternative to traditional manufacturing in the aeronautical sector due to its potential for weight reduction. This research work was developed with data and case studies from an aircraft manufacturer and presents a holistic evaluation of the potential of additive manufacturing regarding, not only technical performance but also cost reduction and environmental sustainability including the use phase of an aircraft. The findings demonstrate that AM can significantly lower life-cycle costs for components with high criticality, achieving up to a 39% reduction compared to traditional manufacturing, even for parts with simple design requirements. This analysis underscores the importance of incorporating post-processing considerations, which account for 13% of the life cycle cost, into both economic and environmental models to ensure informed decision-making. Finally, this study also highlights the importance of optimizing printing strategies as different orientations can influence manufacturing costs.

© 2025 Emerald Publishing LimitedPurpose – This paper aims to assess the feasibility of using additive manufacturing (AM) to produce a gas-turbine’s fuel swirler, thereby validating its suitability for this fabrication process. This study involves a statistical comparison of the AM process with other manufacturing methods, utilizing a multi-criteria decision-making approach to determine the most favorable method for the component. This study also includes the manufacturing of the component and an evolution of the quality control results to ascertain the component’s compliance with required standards. Design/methodology/approach – To compare the different fabrication methods, this paper uses the analytic hierarchy process to compare AM with alternative manufacturing processes, generating different scenarios for comparison. In addition, two samples of the component were additively manufactured to assess their suitability for application in a small gas turbine. Findings – The results indicate that AM was identified as eligible and adequate process for producing the fuel swirler in most scenarios. This study includes the results of a nondestructive quality control process and provides a comprehensive discussion aiming to optimize the component’s quality. These results support the potential for scaling up the production of this component and identifying other components that may benefit from AM. Originality/value – This research contributes to the advancement of technical knowledge regarding the application of an innovative manufacturing method for jet engine components. It aims to enhance manufacturing capabilities for different thermal machine parts while reducing design costs.

©2024 Luiz Vitor Tozi, João Vidal, Jesuino Takachi Tomita, Anderson Vicente Borille, Cleverson Bringuenti, Alexandre Roma, Henrique Rodrigues Oliveira.The industry and the academy are continuously developing new technologies and approaches regarding the gas turbine manufacturing. Logically, sectors of turbomachinery and aerospace engineering are deeply focused on applying newer and even unconventional manufacturing process, aiming on cost reduction, reduced lead times and efficiency. In addition, it is conspicuous that metal additive manufacturing (AM) technologies can provide interesting possibilities for companies seeking to innovate and perfect existing components, with respect to reach better buy-to-fly ratios. In this paper, the authors developed a proposal for additively manufacturing a fuel swirler and evaluated in detail its process of fabrication in order to compare the results with the characteristic of a conventionally manufactured swirler. Furthermore, a dedicated review of the state-of-the-art related to the AM of fuel swirlers were realized to evaluate the relevance of this topic to conclude if the use of AM to fabricate this component can favor the aerospace industry.

© 2023 The Authors.Market movement towards sustainability and electromobility impose new demands on the gear Industry in terms of materials, design and manufacturing. In this context, laser powder bed fusion (L-PBF) has been under the spotlight for being one of the most promising technologies in additive manufacturing (AM), allowing the designer to think beyond traditional constraints. On the other hand, anisotropic properties, distortions, and heterogeneous residual stress may lead to excessive stress states during finishing processes. For carburizing materials, such as 20MnCr5, the mechanisms leading to residual stress and distortions go beyond the temperature gradient mechanism (TGM) and incorporate significant microstructural changes due to phase transformation. The combination of these phenomena with the gear manufacturing chain places a significant challenge to the gear industry. Therefore, this study investigates the potential and challenges of manufacturing 20MnCr5 gears through L-PBF with focus on the surface integrity evolution along the manufacturing chain. The study addresses the processability of the material and investigates the surface integrity of the gears through the manufacturing chain. The composition of thermal and microstructural phenomena simultaneously occurring during print generates heterogeneous residual stress along the gear orientation. Contrary to the literature, the stress relief did not equalize the residual stress entirely. Therefore, the heterogeneous residual stress distribution observed in the as-built condition propagated through the entire chain. Even after three manufacturing operations, the pattern of residual stress after printing directly influenced the final residual stress state.

© 2021, Korean Society for Precision Engineering.Powder metallurgy represents an alternative to increase sustainability in the manufacturing of automotive gears, but its potential is hindered by a certain lack of knowledge on surface integrity properties that can impair the gear performance. This study explores the effects of the microstructural differences induced by this chain on the residual stress heterogeneity state of gears. X-ray diffraction methods of macro residual stress mapping and line profile analysis were applied for measurements of gear teeth after subsequent steps of the powder metallurgy and the conventional wrought steel chains. The powder metallurgy chain induced more pronounced heterogeneities than the conventional manufacturing, characterized by non-uniform residual stress distributions along the lead and the involute profiles of gear flanks. These non-uniformities observed after carburizing were traced back to the previous steps, surface densification, sintering and compaction. The residual stress distribution patterns of these steps were compatible with the plasticity dynamics of each manufacturing process. Such surface integrity heterogeneities result in a residual stress gradient along the gears functional surface, exposing particular regions to be more susceptible to fatigue effects.

© 2022 The Authors.The evolution of residual stress (RS) induced by laser powder bed fusion (L-PBF) along post-processing steps of automotive carburizing steels is a topic still underexplored by the scientific community. In this study, L-PBF specimens of 20MnCr5 steel produced with different build orientations were subjected to the same stress relief, milling and carburizing steps. RS and the diffractogram full width of half maximum (FWHM) depth profiles obtained through X-ray diffraction were compared along the manufacturing chains. It was shown that the previous manufacturing steps influence the final RS state, from L-PBF to carburizing.

© 2025, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.Adaptive refinement methods can help speed up expensive simulations by reducing the amount of user-dependent processes during mesh generation. One of the most crucial steps in these methods is identifying regions requiring spatial resolution interventions. One of the most straightforward ways of doing this is using featured-based indicators. Because of their general simplistic nature, they may be inefficient in detecting problematic elements under specific numerical circumstances. The current work seeks to analyze these indicators in the context of spectral/hp discretization using continuous Galerkin. We categorized the indicators into three groups: jump, spectral, and error-based. The first two had their performance tested, while the last was employed as a reference. We analyzed them using multiple one-dimensional and one two-dimensional tests to verify how different feature-based indicators perform in distinct numerical circumstances. To measure their performance, we analyze their capability to decrease discretization error when guiding a sequence of p-adaptation cycles. The indicator that performed most consistently well was based on the maximum derivative jump.

© The Author(s), under exclusive licence to The Brazilian Society of Mechanical Sciences and Engineering 2024.This study focuses on 2D RANS (Reynolds Averaged Navier-Stokes) simulations using Spalart-Allmaras and k- ω SST turbulence models for a supersonic air inlet featuring two different passive control systems: an air bleed system in the external ramp of the inlet and a two-dimensional bump. The supersonic inlet serving to capture and decelerate the high-speed incoming flows is aerodynamically indispensable to an airbreathing supersonic aircraft. Sometimes, depending on the conditions of the entry flow, the shock wave boundary layer interaction (SWBLI) can lead to inlet unstart if not controlled, due to thickened boundary layer. To verify the impact of the passive control systems, the inlet was tested at freestream Mach number of 2.0 and 2.03 as the geometry is very sensitive to Mach number change. Results indicate that the air bleed system is more effective for Mach 2.0 and reduces the bubble size of approximately 80.0%. In the case of the two-dimensional bump, it was noticed that the bump should be placed after the impinging shock on the geometry. Even though the bubble size does not reduce as much as for the air bleed system, for the two-dimensional bump, the SWBLI is weakened.

© 2024 Elsevier B.V.We present a new linear eigensolution analysis technique that provides superior estimates of dissipation distribution in wavenumber space for the continuous Galerkin (CG) method. The technique builds upon traditional dispersion–diffusion analyses that have been applied to spectral/hp element methods, but in particular is an improvement upon the non-modal eigenanalysis approach proposed by Fernandez et al. (2019). The present technique takes into account the indirect effects that dispersion may have on dissipation, as recently discussed by Moura et al. (2022), in order to better represent dissipation itself. Also, a concept used by the dynamic mode decomposition (DMD) community is invoked to weight the relative contribution of the multiple diffusion curves that stem from temporal eigenanalysis. This allows for obtaining a single dissipation profile in wavenumber space, so that the proposed technique is named joint-mode analysis. Although the non-modal approach also provides a single diffusion curve, the joint-mode dissipation curve is shown to correlate significantly better with the energy spectrum of Burgers’ turbulence at large and intermediate scales, which is particularly relevant for implicit large-eddy simulation (LES). The proposed technique is readily extensible to other spectral/hp element methods.

© 2024 Elsevier Inc.We present a new linear eigensolution analysis technique that provides superior estimates of dissipation distribution in wavenumber space for the discontinuous Galerkin (DG) method. The technique builds upon traditional dispersion-diffusion analyses that have been applied to spectral/hp element methods, but in particular is an improvement upon the non-modal eigenanalysis approach proposed by Fernandez et al. in [1]. The present technique takes into account the indirect effects that dispersion may have on dissipation, as recently discussed by Moura et al. in [2], in order to better represent dissipation itself. Also, a concept often used with dynamic mode decomposition (DMD) techniques is invoked to weight the relative contribution of the multiple diffusion curves that stem from temporal eigenanalysis. This allows for obtaining a single dissipation profile in wavenumber space, so that the proposed technique is named joint-mode analysis. Although the non-modal approach also provides a single diffusion curve, the joint-mode dissipation curve is shown to correlate significantly better with the energy spectrum of Burgers' turbulence at large and intermediate scales, which is particularly relevant for implicit large-eddy simulation (LES). The proposed technique is readily extensible to other spectral/hp element methods.

© The Author(s), 2023. Published by Cambridge University Press.We present the results of direct numerical simulations of a NACA 0012 airfoil, with Mach number 0.3 and angle of attack of, examining the dynamics of the flow with increasing Reynolds numbers. Two-dimensional simulation results are obtained with chord-based Reynolds numbers in the range, where each simulation uses the last time step of the previous one as a starting point, to capture the evolution of dynamics as a function of. The development of the pressure fluctuations with time shows a transition from periodic to quasi-periodic attractor for, leading to the emergence of secondary tones in the wall and acoustic field pressure spectra, different from peaks related to the fundamental frequency and the respective harmonics; a second, incommensurate frequency appears, leading to several secondary tones with frequency, with and integers. Further increase of the Reynolds number leads to the emergence of a tertiary frequency, indicating a route to chaos of the Ruelle-Takens-Newhouse type. Such a mechanism is related to the ladder-type characteristic structure of the tones, indicating that dynamic systems theory is an important tool for understanding airfoil tonal noise.

© 2023, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.When solving differential equations, one must often use spatial discretization. However, this process introduces errors that are mesh dependent. Thus, improving solution quality while saving computational resources requires adequate spatial resolution. One way of doing so is to treat this issue as an optimization problem that targets the reduction of discretization error. The current work presents an approach to mesh optimization using r-adaptation and the adjoint method for one-dimensional steady equations. The two equations selected to display this methodology are the heat equation with a forcing term and the viscous burgers equation. The discretization method is a second-order finite differences scheme. The results present a substantial reduction in discretization error when the optimized meshes are employed.

© 2023, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.Up to this day, the Computational Fluid Dynamics (CFD) field struggles to generate accurate and computationally viable turbulent flow simulations for aeronautical problems. The absence of a proper spatial resolution reduces the accuracy of simulations and may lead to nonphysical results and numerical instabilities. This problem may be addressed by increasing the number of degrees of freedom in the simulation. Since this also leads to higher computational costs, this process must be performed parsimoniously and focus on where it is the most efficient. However, the process of identification and refinement of those regions can be far from trivial. The current work is an initial step to investigate the performance of adaptation drivers that can be used to make industrial simulations more viable. The drivers are based on a jump indicator for high-order spectral/hp schemes. It takes the difference between averaged values on overlapping borders of two different elements as a measurement of error. The chosen adaptation method is a p-adaptation framework that increases the polynomial order of 10% of the mesh elements. The governing equations employed in the study are the two-dimensional Navier-Stokes equations, and the simulated test case is one of a tilted flat plate.

© 2022 Elsevier Inc.In recent years, different dispersion-diffusion (eigen)analyses have been developed and used to assess various spectral element methods (SEMs) with regards to accuracy and stability, both of which are very important aspects for under-resolved computations of transitional and turbulent flows. Not surprisingly, eigenanalysis has been used recurrently to probe the inner-workings of SEM-based implicit LES approaches, where numerical dissipation acts alone in lieu of a subgrid model. In this study we present and discuss an intriguing linear mechanism that causes energy transfer across Fourier modes as seen in the energy spectrum of SEM computations. Despite its linear nature, this mechanism has not been considered in eigenanalyses so far, possibly due to its connection to the often overlooked multiple eigencurves feature of periodic eigenanalysis. As we unveil the mechanism in the simplified context of linear advection, we point out how its effects might take place in actual turbulence simulations. In particular, we highlight how taking it into account in eigenanalysis can improve dissipation estimates in wavenumber space, potentially allowing for a superior correlation between dissipation estimates and energy spectra measured in SEM-based eddy-resolving turbulence computations.

© 2022, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.An aircraft flying under icing conditions tends to accumulate ice on aerodynamic surfaces which deteriorates aircraft performance and may affect safety. Recent work obtained, via 3D-scanning, high-fidelity characterization of ice shapes generated in the NASA-CRM model swept wing in the NASA IRT icing wind tunnel. These shapes are highly three-dimensional and in order to better understand and isolate the effects of the three-dimensional parameters, various simplified shapes were built and tested in aerodynamic wind tunnels to compare the results with the high-fidelity representation. Even with this geometrical break-down, the aerodynamic phenomena that takes place in the highly swept wing of the NASA-CRM model are complex. The present work takes a step backwards in the complexity level, evaluating the threedimensional shapes effect on NACA 23012 airfoil, to provide basis for a better understanding of the NASA-CRM icing tests. The effects of horn ice shapes with different spanwise gaps sizes and orientations were evaluated by testing artificial ice shapes on the leading edge of a NACA 23012 airfoil under low-Reynolds-number conditions. The lift, drag, pitching moment and pressure distribution were measured for the clean airfoil and six ice shapes built. The aerodynamic performance and PIV measurements for each of these geometries are compared with its extruded 2D counterpart and clean airfoil configuration. The results regarding the size of the gaps in the ice shapes, showed that the increase in the gap widths directly improved airfoil performance. The PIV flow fields helped identify flow reattachment downstream the horn bubble for ice shapes with gaps. The surface oil visualization for the oriented ice shapes helped understand certain patterns and influence of the cross flow past the horn.

© 2022, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.It is well-known that ice accretion can adversely impact the aerodynamic performance of airfoils and wings. In this work, we conducted an experimental investigation on the impact of different ice shapes on the flow around airfoils. The NACA 23012 and the GLC-305 airfoils were tested at a low-reynolds wind tunnel, which included forces, moments and surface pressure were evaluated, and Particle Image Velocimetry (PIV) was used for flow field measurement. The studied ice type was a simulated single horn based on the glaze ice accreted on airfoil leading edge, with different heights and chord position. The parametric approach was applied in order to vary the ice geometric characteristics. Evaluation was performed with the ice shape extruded throughout the entire span of the airfoil, and the objective of this research was to provide a flowfield-physics perspective on the flow with different ice geometries and its effect on the overall aerodynamic performance of the airfoil under low Reynolds conditions.

© 2021 Elsevier B.V.One of the strengths of the discontinuous Galerkin (DG) method has been its balance between accuracy and robustness, which stems from DG's intrinsic (upwind) dissipation being biased towards high frequencies/wavenumbers. This is particularly useful in high Reynolds-number flow simulations where limitations on mesh resolution typically lead to potentially unstable under-resolved scales. In continuous Galerkin (CG) discretisations, similar properties are achievable through the addition of artificial diffusion such as spectral vanishing viscosity (SVV). However although SVV is recognised as very useful in CG-based high-fidelity turbulence simulations, this approach has been observed to be sub-optimal when compared to DG at intermediate polynomials orders (P≈3). In this paper we explore an alternative stabilisation approach through the introduction of a continuous interior penalty on the gradient discontinuity at elemental boundaries, which we refer to as a gradient jump penalisation (GJP). Analogous to DG methods, this introduces a penalisation at the elemental interfaces as opposed to the interior element stabilisation of SVV. Detailed eigenanalysis of the GJP approach shows its potential as equivalent (sometimes superior) to DG dissipation and hence superior to previous SVV approaches. Through eigenanalysis, a judicious choice of GJP's P-dependent scaling parameter is made and found to be consistent with previous a-priori error analysis. The favourable properties of the GJP stabilisation approach are also supported by turbulent flow simulations of the incompressible Navier–Stokes equation, as we achieve higher quality flow solutions at P=3 using GJP, whereas SVV performs marginally worse at P=5 with twice as many degrees of freedom in total.

© 2025 The Author(s).We study the hydrodynamic and acoustic fields of turbulent jets issuing from nozzles modified by the addition of cylindrical tabs on the inner surface, one diameter upstream of the exit. The tabs are designed to promote significant growth of steady streaks in the nozzle turbulent boundary layer. A baseline smooth nozzle is also studied for comparison. Acoustic measurements are made using an azimuthal array for Mach numbers in the range 0.4 0.9. The tabs are found to reduce the emitted sound levels by up to 3 dB/St. In terms of overall sound pressure levels, reductions of up to 3 dB are observed at all measured polar angles in the range 20° 90°. Time-resolved particle image velocimetry experiments are conducted to measure the three components of velocity for a series of cross-stream planes at 0.7. A Floquet-based Fourier decomposition is applied for the azimuthally periodic flow field, and spectral proper orthogonal decomposition is then employed to extract coherent structures. Comparison of the structures obtained for nozzles with and without tabs shows an enhancement of the streaky structures by the tabs and a damping of Kelvin-Helmholtz wavepackets. A linear model based on the one-way Navier-Stokes equations is employed to explore the underlying amplification mechanisms and how these are impacted by the tabs. The model reproduces the growth-attenuation mechanism observed in the data, showing that the changes in the mean flow induced by the streaks work to reduce the amplification of the noise-generating coherent structures associated with linear spatial growth mechanisms.

© The Author(s), 2025. Published by Cambridge University Press.This work investigates the receptivity mechanisms of a NACA0008 airfoil to a level of free-stream turbulence (FST) through a direct numerical simulation (DNS) and an associated linearised simulation on the same mesh. By comparing velocity perturbation fields between the two simulations, the study reveals that the streaky structures that degenerate into turbulent spots are predominantly influenced by nonlinear convective terms, rather than the linear amplification of inflow perturbations around the laminar base flow. A power spectral analysis shows differences in the energy distribution between the DNS and linearised simulation, with the DNS containing more energy at higher wavenumbers, for structures located near the airfoil's leading edge. Representative wavenumbers are identified through modal analysis, revealing a dynamics dominated by streak-like structures. The study employs the Nek5000 numerical solver to distinguish between linear and nonlinear receptivity mechanisms over the NACA0008 airfoil, highlighting their respective contributions to the amplification of perturbations inside the boundary layer. In the high FST case studied, it is observed that the energy of the incoming turbulence is continuously transferred into the boundary layer along the length of the wing. The nonlinear interactions generate streaks with higher spanwise wavenumbers compared with those observed in purely linearised simulations. These thinner streaks align with the spanwise scales identified as susceptible to secondary instabilities. Finally, the procedures presented here generalise the workflow of previous works, allowing for the assessment of receptivity for simulations with arbitrary mesh geometries.

©2025 American Physical SocietyThis study investigates the two- and three-dimensional convective and absolute instability characteristics of planar viscoelastic jet flows using the Oldroyd-B and Giesekus models. Analyzing instability in different types of flows is fundamental for understanding their behavior in various natural and industrial applications. Convective instability refers to disturbances that propagate and grow downstream, while absolute instability involves disturbances that grow over time regardless of their position in the flow. Understanding these phenomena can help optimize industrial processes and predict complex flow behaviors, for example. Results indicate that concerning convective instability, the Giesekus model exhibits a larger unstable region compared to the Oldroyd-B and Newtonian models. On the other hand, the Oldroyd-B model is more susceptible to absolute instability than the Giesekus model. Notably, in the Giesekus model, the mobility parameter αG significantly influences the occurrence of absolute instability, which only occurs for small values of αG, for which the fluid tends to the Oldroyd-B behavior. For the tested parameters, only low values of αG (close to the Oldroyd-B model, which corresponds to αG = 0) led to the emergence of absolute instability, while larger values did not. These observations apply to both two-dimensional and three-dimensional disturbances.

© The Author(s), 2025. Published by Cambridge University Press.This paper presents an experimental application of reactive control to jet installation noise based on destructive interference. The work is motivated by the success of previous studies in applying this control approach to mixing layers (Sasaki et al. Theor. 2018b Comput. Fluid Dyn. 32, 765-788), boundary layers (Brito et al. 2021 Exp. Fluids 62, 1-13; Audiffred et al. 2023 Phys. Rev. Fluids 8, 073902), flow over a backward-facing step (Martini et al. 2022 J. Fluid Mech. 937, A19) and, more recently, to turbulent jets (Maia et al. 2021 Phys. Rev. Fluids 6, 123901; Maia et al. 2022 Phys. Rev. Fluids 7, 033903; Audiffred et al. 2024b J. Fluid Mech. 994, A15). We exploit the fact that jet-surface interaction noise is underpinned by wavepackets that can be modelled in a linear framework and develop a linear control strategy where piezoelectric actuators situated at the edge of a scattering surface are driven in real time by sensor measurements in the near field of the jet, the objective being to reduce noise radiated in the acoustic field. The control mechanism involves imposition of an anti-dipole at the trailing edge to cancel the scattering dipole that arises due to an incident wavepacket perturbation. We explore two different control strategies: (i) the inverse feed-forward approach, where causality is imposed by truncating the control kernel, and (ii) the Wiener-Hopf approach, where causality is optimally enforced in building the control kernel. We show that the Wiener-Hopf approach has better performance than that obtained using the truncated inverse feed-forward kernel. We also explore different positions of the near-field sensors and show that control performance is better for sensors installed for streamwise positions downstream in the jet plume, where the signature of hydrodynamic wavepacket is better captured by the sensors. Broadband noise reductions of up to 50 % are achieved.

© The Author(s), 2025. Published by Cambridge University Press. This is an Open Access article,In a combined experimental and numerical effort, we investigate the generation and reduction of airfoil tonal noise. The means of noise control are streak generators in the form of cylindrical roughness elements. These elements are placed periodically along the span of the airfoil at the mid-chord streamwise position. Experiments are performed for a wide range of Reynolds numbers and angles of attack in a companion work (Alva et al., AIAA Aviation Forum, 2023). In the present work, we concentrate on numerical investigations for a further investigation of selected cases. We have performed wall-resolved large-eddy simulations for a NACA 0012 airfoil at zero angle of attack and Mach 0.3. Two Reynolds numbers (0.8 × 105 and 1.0 × 105) have been investigated, showing acoustic results consistent with experiments at the same Reynolds but lower Mach numbers. Roughness elements attenuate tones in the acoustic field and, for the higher Reynolds number, suppress them. Through Fourier decomposition and spectral proper orthogonal decomposition analysis of streamwise velocity data, dominating structures have been identified. Further, the coupling between the structures generated by the surface roughness and the instability modes (Kelvin–Helmholtz) of the shear layer has been identified through stability analysis, suggesting stabilisation mechanisms by which the sound generation by the airfoil is reduced by the roughness elements.

© The Author(s), 2025. Published by Cambridge University Press.We explore a reduced-order model (ROM) of plane Couette flow with a view to performing near-wall turbulence control. The ROM is derived through Galerkin projections of the incompressible Navier–Stokes system onto a basis of controllability modes. Such ROMs were found to reproduce key aspects of turbulence dynamics in Couette flow with only a few hundred degrees of freedom, and here we use them to devise a control strategy. We consider a ROM with an extra forcing term whose structure is given by a combination of eigenfunctions of a linear viscous diffusion equation, optimised in order to minimise the total fluctuation energy. The optimisation is performed at Reynolds numbers Re = 1000, 2000, 3000, and produces a novel control mechanism wherein the optimal forcing leads the flow to laminarisation in all cases. The forcing acts by reducing the shear in a large portion of the channel, hindering the main energy input mechanism. The forced flow possesses a new laminar solution which is linearly stable at Re = 1000 and unstable at higher Re, but whose transient growth of streaky structures is substantially lower than that of laminar Couette flow, leading the flow to full laminarisation when the forcing is removed. Forcings optimised in the ROM are subsequently applied in direct numerical simulations (DNS). The same control mechanisms are observed in the DNS, where laminarisation is also achieved. We show that the ROMs provide an effective framework to design turbulence control strategies, despite the high degree of truncation, which opens up interesting possibilities for turbulence control.

© 2025 Acoustical Society of America.This study explores the use of parabolized stability equations (PSEs) for predicting sound propagation in ducts, a novel application in computational duct acoustics. The PSE, formulated in a general duct-fitted coordinate system, was validated against several test cases, including uniform flow, axial temperature gradients, and laminar/turbulent flows, demonstrating close agreement with existing literature. This paper highlights limitations of the PSE, particularly when the local Helmholtz number decreases, potentially causing mode cutoff, and suggests remedies for mitigating phase and amplitude errors. The efficiency of the PSE is further demonstrated through a comparison with linearized Euler equations for forward fan noise propagation in a turbofan inlet, showing 75.8% reduced computational time and 98.2% reduced memory usage. These computational advantages become more significant as problem size increases, with the PSE outperforming traditional finite element and parabolic approximation methods, especially in cases involving viscous shear flow effects. This makes the PSE particularly well-suited for applications such as boundary layer shielding and liner-boundary layer interactions. The study provides a promising avenue for future acoustic research and practical engineering applications, emphasizing the efficiency and accuracy of PSE in complex duct acoustics.

© The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature 2024.This work aims to provide a more complete understanding of the resonance mechanisms that occur in turbulent jets at high subsonic Mach number, as shown by Towne et al. (J. Fluid Mech., vol. 825, 2017, pp. 1113-1152). Resonance was suggested by that study to exist between upstream- and downstream-travelling guided waves. Five possible resonance mechanisms were postulated, each involving different families of guided waves that reflect in the nozzle exit plane and at a number of downstream turning points. However, that study did not identify which of the five resonance mechanisms underpin the observed spectral peaks. In this work, the waves underpinning resonance are identified via a biorthogonal projection of Large Eddy Simulation data on eigenbases provided by a locally parallel linear stability analysis. Two of the five scenarios postulated by Towne et al. are thus confirmed to exist in the turbulent jet. The reflection-coefficients in the nozzle exit and turning-point planes are, furthermore, identified. Such information is required as input for simplified resonance-modelling strategies such as developed in Jordan et al. (J. Fluid Mech., vol. 853, 2018, pp. 333-358) for jet-edge resonance, and in Mancinelli et al. (Exp. Fluids, vol. 60, 2019, pp. 1-9) for supersonic screech.

© 2025 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.The Actuator Line Method (ALM) is a technique that replaces the detailed airfoil geometry with distributed body forces to predict the flow field. ALM has been widely employed for simulating rotating blade wakes due to its flexibility and accuracy in the far field. In this study, the applicability of ALM for unsteady aerodynamics and acoustic field prediction is evaluated. The case study considered is the harmonic transverse oscillation of a thin airfoil in uniform flow. The ALM body forces are distributed over a few grid points following a Gaussian function, with a range of smearing ratio of ε/c (smearing parameter over the chord length) between 0.4 and 1. These forces are computed using thin airfoil theory with the Prandtl-Glauert correction for compressible regime. Based on these computations, the compressible Navier-Stokes equations are numerically solved, yielding the velocity and pressure fields. ALM lift results are validated against unsteady aerodynamic theory in the subsonic regime. Moreover, results demonstrate an acoustic field consistent with a dipole distribution and a spectrum exhibiting a frequency corresponding to the plunging motion. Furthermore, the acoustic results are validated through an acoustic analogy approach, involving the prediction of the acoustic field via Green’s function. The prediction of the acoustic far-field using ALM is expected to significantly reduce the computational cost of compressible simulations applied to propeller and wind turbine aeroacoustics.

© The Author(s), 2024.Guided-jet waves have been shown to close resonance loops in a myriad of problems such as screech and impingement tones in jets. These discrete, upstream-travelling waves have long been identified in linear-stability models of jet flows, but in this work they are instead considered in the context of an acoustic-scattering problem. It is shown that the guided-jet mode results from total internal reflection and transmission of acoustic waves, arising from the shear layer behaving like a duct with some given wall impedance. After total reflection, only discrete streamwise wavenumbers may be supported by the flow, with these wavenumbers dictated by the fact that the standing wave formed inside of the jet must fit between the two shear layers. Close to the sonic line, the transmission of this mode to the outside is maximum, leading to a net-energy flux directed upstream, which dictates the direction of propagation of this mode, providing a clear connection to the better understood soft-duct mode (Towne et al., J. Fluid Mech., vol. 825, 2017, pp. 1113-1152). The model also indicates that these waves are generated in the core of the flow and can only be efficiently transmitted to the quiescent region under certain conditions, providing an explanation as to why screech is only observed at conditions where the discrete mode is supported by the flow. The present results explain, for the first time, the nature and characteristics of the guided-jet waves.

© The Author(s), 2024. Published by Cambridge University Press.We present an experimental study of reactive control of turbulent jets, in which we target axisymmetric coherent structures, known to play a key role in the generation of sound. We first consider a forced jet, in which coherent structures are amplified above background levels, facilitating their detection, estimation and control. We then consider the more challenging case of an unforced jet. The linear control targets coherent structures in the region just downstream of the nozzle exit plane, where linear models are known to be appropriate for description of the lowest-order azimuthal modes of the turbulence. The control law is constructed in frequency space, based on empirically determined transfer functions. And the Wiener–Hopf formalism is used to enforce causality and to provide an optimal controller, as opposed to the sub-optimal control laws provided by simpler wave-cancellation methods. Significant improvements are demonstrated in the control of both forced and unforced jets. In the former case, order-of-magnitude reductions are achieved; and in the latter, turbulence levels are reduced by up to 60 %. The results open new perspectives for the control of turbulent flow at high Reynolds number.

© The Author(s), under exclusive licence to Springer Nature B.V. 2023.A comparative study of the acoustic far-field radiation of a subsonic jet near a folded plate with an opening, intended to represent a flapped wing with thrust gate, is presented in this work. Three openings with different widths were used to evaluate experimentally the influence of the gaps in the far-field noise radiation, for two folding angles. Boundary Element Method simulations with a wavepacket model which represents the jet acoustic source are used to calculate the far-field noise. Numerical simulation results are compared with experimental measurements and show similar trends in terms of acoustic radiation. Through parametric simulations, it was also possible to estimate that opening widths greater than one jet diameter do not contribute significantly to reducing the far-field noise. The results show that even the smallest tested openings were able to reduce the far-field noise for the tested positions.

© The Author(s), 2024. Published by Cambridge University Press.The low-frequency modal and non-modal linear dynamics of an incompressible, pressure-gradient-induced turbulent separation bubble (TSB) are investigated, with the objective of studying the mechanism responsible for the low-frequency contraction and expansion (breathing) commonly observed in experimental studies. The configuration of interest is a TSB generated on a flat test surface by a succession of adverse and favourable pressure gradients. The base flow selected for the analysis is the average TSB from the direct numerical simulation of Coleman et al. (J. Fluid Mech., vol. 847, 2018, pp. 28-70). Global mode analysis reveals that the eigenmodes of the linear operator are damped for all frequencies and wavenumbers. Furthermore, the least damped eigenmode appears to occur at zero frequency and low, non-zero spanwise wavenumber when scaled with the separation length. Resolvent analysis is then employed to examine the forced dynamics of the flow. At low frequency, a region of low, non-zero spanwise wavenumber is also discernible, where the receptivity appears to be driven by the identified weakly damped global mode. The corresponding optimal energy gain is shown to have the shape of a first-order, low-pass filter with a cut-off frequency consistent with the low-frequency unsteadiness in TSBs. The results from resolvent analysis are compared to the unsteady experimental database of Le Floc'h et al. (J. Fluid Mech., vol. 902, 2020, A13) in a similar TSB flow. The alignment between the optimal response and the first spectral proper orthogonal decomposition mode computed from the experiments is shown to be close to, while the spanwise wavenumber of the optimal response is consistent with that of the low-frequency breathing motion captured experimentally. This indicates that the fluctuations observed experimentally at low frequency closely match the response computed from resolvent analysis. Based on these results, we propose that the forced dynamics of the flow, driven by the weakly damped global mode, serve as a plausible mechanism for the origin of the low-frequency breathing motion commonly observed in experimental studies of TSBs.

© 2024 American Physical Society.Most of the studies on pressure fluctuations in wall-bounded turbulent flows aim at obtaining statistics as power spectra and scaling laws, especially at the walls. In the present study we study energetic coherent pressure structures of turbulent channel flows, aiming at a characterization of dominant coherent structures throughout the channel. Coherent structures are detected using spectral proper orthogonal decomposition (SPOD) and modeled using resolvent analysis, similarly to related works dealing with velocity fluctuations but this time using pressure fluctuations as the output of interest. The resolvent operator was considered with and without the Cess eddy-viscosity model. Direct numerical simulations (DNSs) of incompressible turbulent channel flows at friction Reynolds numbers of approximately 180 and 550 were employed as databases in this study. Three representative dominant structures emerged from a preliminary spectral analysis: near-wall, large-scale, and spanwise-coherent structures. For frequency-wave number combinations corresponding to these three representative structures, SPOD results show a strong dominance of the leading mode, highlighting low-rank behavior of pressure fluctuations. The leading resolvent mode closely agrees with the first SPOD mode, providing support to studies that showed better performance of resolvent-based estimators when predicting pressure fluctuations compared to velocity fluctuations [Amaral, J. Fluid Mech. 927, A17 (2021)JFLSA70022-112010.1017/jfm.2021.764]. The dominant mechanisms of the analyzed modes are seen to be the generation of quasistreamwise vortices with pressure fluctuations appearing close to vortex centers. A study on the individual contributions of the nonlinear terms (treated as forcing in resolvent analysis) to the pressure output reveals that each forcing component plays a constructive role to the input-output formulation, which also helps understanding the weaker role of forcing "color"in driving pressure fluctuations.

© The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature 2024.Abstract: We study generalised quasilinear (GQL) approximations applied to turbulent plane Couette flow. The GQL framework is explored in conjunction with a Galerkin reduced-order model (ROM) recently developed by Cavalieri and Nogueira (Phys Rev Fluids 7:102601, 2022), which considers controllability modes of the linearised Navier–Stokes system as basis functions, representing coherent structures in the flow. The velocity field is decomposed into two groups: one composed by high-controllability modes and the other by low-controllability modes. The former group is solved with the full nonlinear equations, whereas the equations for the latter are linearised. We also consider a new GQL framework wherein the linearised equations for the low-controllability modes are driven by nonlinear interactions of modes in the first group, which are characterised by large-scale coherent structures. It is shown that GQL-ROMs successfully recover the statistics of the full model with relatively high controllability thresholds and sparser nonlinear operators. Driven GQL-ROMs were found to converge more rapidly than standard GQL approximations, providing accurate description of the statistics with a larger number of linearised modes. This indicates that the forcing of linearised flow structures by large-scale coherent structures is an important feature of turbulence dynamics that should be considered in GQL models. The results presented here reveal that further model reductions are attainable with GQL-ROMs, which can be valuable to extend these models to larger Reynolds numbers. Graphical abstract: (Figure presented.)

© The Author(s), 2024. Published by Cambridge University Press.We study the stability of a zero-pressure gradient boundary layer subjected to free-stream disturbances by means of local stability analysis. The dataset under study corresponds to a direct numerical simulation (DNS) of a flat plate with a sharp leading edge in realistic wind tunnel conditions, with a turbulence level of 3.45 % at the leading edge. We present a method to track the convective evolution of the secondary instabilities of streaks by performing sequential stability calculations following the wave packet, connecting successive unstable eigenfunctions. A scattered nature, in time and space, of secondary instabilities is seen in the stability calculations. These instabilities can be detected before they reach finite amplitude in the DNS, preceding the nucleation of turbulent spots, and whose appearance is well correlated to the transition onset. This represents further evidence regarding the relevance of secondary instabilities of streaks in the bypass transition in realistic flow conditions. Consistent with the spatio-temporal nature of this problem, our approach allows us to integrate directly the local growth rates to obtain the spatial amplification ratio of the individual instabilities, where it is shown that instabilities reaching an -factor in the range [2.5,4] can be directly correlated to more than 65 % of the nucleation events. Interestingly, it is found that high amplification is not only attained by modes with high growth rates, but also by instabilities with sustained low growth rates for a long time.

© The Author(s), 2024. Published by Cambridge University Press.Thin airfoil dynamic stall at moderate Reynolds numbers is typically linked to the sudden bursting of a small laminar separation bubble close to the leading edge. Given the strong sensitivity of laminar separation bubbles to external disturbances, the onset of dynamic stall on a NACA0009 airfoil section subject to different levels of low-amplitude free stream disturbances is investigated using direct numerical simulations. The flow is practically indistinguishable from clean inflow simulations in the literature for turbulence intensities at the leading edge of. At slightly higher turbulence intensities of, the bursting process is found to be considerably less smooth and strong coherent vortex shedding from the laminar separation bubble is observed prior to the formation of the dynamic stall vortex (DSV). This phenomenon is considered in more detail by analysing its appearance in an ensemble of simulations comprising statistically independent realisations of the flow, thus proving its statistical relevance. In order to extract the transient dynamics of the vortex shedding, the classical proper orthogonal decomposition method is generalised to include time in the energy measure and applied to the time-resolved simulation data of incipient dynamic stall. Using this technique, the dominant transient spatiotemporally correlated features are distilled and the wave train of the vortex shedding prior to the emergence of the main DSV is reconstructed from the flow data exhibiting dynamics of large-scale coherent growth and decay within the turbulent boundary layer.

© The Author(s) 2024.Abstract: This study presents a physics-based, low-order model for the trailing edge (TE) noise generated by an airfoil at low angle of attack. The approach employs incompressible resolvent analysis of the mean flow to extract relevant spanwise-coherent structures in the transitional boundary layer and near wake. These structures are integrated into Curle’s solution to Lighthill’s acoustic analogy to obtain the scattered acoustic field. The model has the advantage of predicting surface pressure fluctuations from first principles, avoiding reliance on empirical models, but with a free amplitude set by simulation data. The model is evaluated for the transitional flow (Re=5e4) around a NACA0012 airfoil at 3 deg angle of attack, which features TE noise with multiple tones. The mean flow is obtained from a compressible large eddy simulation, and spectral proper orthogonal decomposition (SPOD) is employed to extract the main hydrodynamic and acoustic features of the flow. Comparisons between resolvent and SPOD demonstrate that the physics-based model accurately captures the leading coherent structures at the main tones’ frequencies, resulting in a good agreement of the reconstructed acoustic power with that of the SPOD (within 4 dB). Discrepancies are observed at high frequencies, likely linked to nonlinearities that are not considered in the resolvent analysis. The model’s directivity aligns well with the data at low Helmholtz numbers, but it fails at high frequencies where the back-scattered pressure plays a significant role in directivity. This modeling approach opens the way for efficient optimization of airfoil shapes in combination with low-fidelity mean flow solvers to reduce TE noise. Graphical abstract: (Figure presented.)

© The Author(s), 2024. Published by Cambridge University Press.Plane Couette flow at Reynolds number Re = 1200 (based on the channel half-height and half the velocity difference between the top and bottom plates) is investigated with a spatial domain designed to retain only two spanwise integral length scales. In this system, the computation of invariant solutions that are physically representative of the turbulent state has been understood to be challenging. To address this challenge, our approach is to employ an accurate reduced-order model with 600 degrees of freedom (Cavalieri & Nogueira, Phys. Rev. Fluids, vol. 7, 2022, L102601). Using the two-scale energy budget and the temporal cross-correlation of key observables, it is first demonstrated that the model contains most of the multi-scale physical processes identified recently (Doohan et al., J. Fluid Mech., vol. 913, 2021, A8); i.e. the large- and small-scale self-sustaining processes, the energy cascade for turbulent dissipation, and an energy-cascade mediated small-scale production mechanism. Invariant solutions of the reduced-order model are subsequently computed, including 96 equilibria and 43 periodic orbits. It is found that none of the computed equilibrium solutions are able to reproduce an accurate energy balance associated with the multi-scale dynamics of the turbulent state. Incorporation of unsteadiness into invariant solutions is seen to be essential for a sensible description of the multi-scale turbulent dynamics and the related energetics, at least in this type of flow, as periodic orbits with a sufficiently long period are mainly able to describe the complex spatio-temporal dynamics associated with the known multi-scale phenomena.

© 2024 Author(s).The widest spanwise scales in turbulent channel flows are studied through the use of three periodic channel-flow simulations at friction Reynolds number Re τ = 550 . The length and height of the channels are the same in all cases ( L x / h = 8 π and L y / h = 2 , respectively), while the width is progressively doubled: L z / h = { 4 π , 8 π , 16 π } . The effects of increasing the domain width cannot be determined with statistical significance in our simulations, since the difference in the statistics between the simulations is of the same order as the errors of convergence. A channel flow similar to the smaller one [Del Álamo et al., “Scaling of the energy spectra of turbulent channels,” J. Fluid Mech. 500, 135-144 (2004)], which was averaged over a very long time, was used as a reference. The one-dimensional spanwise spectrum of the streamwise velocity is computed with the aim of assessing the domain-size effect on the widest scales. Our results indicate that 90% of the total streamwise energetic fluctuations is recovered without a significant influence of the size of the domain. The remaining 10% of the energy reflects that the widest scales in the outer layer are the ones most significantly affected by the spanwise length of the domain. The power-spectral density for kz = 0 remains constant even if the size of the domain in the spanwise direction is increased up to four times the standard spanwise length, indicating that wide, spanwise coherent structures are not an artifact of domain truncation.

© The Author(s) 2023.Abstract: An adjoint-based method is presented for determining manufacturing tolerances for aerodynamic surfaces with natural laminar flow subjected to wavy excrescences. The growth of convective unstable disturbances is computed by solving Euler, boundary layer, and parabolized stability equations. The gradient of the kinetic energy of disturbances in the boundary layer (E) with respect to surface grid points is calculated by solving adjoints of the governing equations. The accuracy of approximations of ΔE, using gradients obtained from adjoint, is investigated for several waviness heights. It is also shown how second-order derivatives increase the accuracy of approximations of ΔE when surface deformations are large. Then, for specific flight conditions, using the steepest ascent and the sequential least squares programming methodologies, the waviness profile with minimum L2-norm that causes a specific increase in the maximum value of N- factor, ΔN, is found. Finally, numerical tests are performed using the NLF(2)-0415 airfoil to specify tolerance levels for ΔN up to 2.0 for different flight conditions. Most simulations are carried out for a Mach number and angle of attack equal to 0.5 and 1.25∘, respectively, and with Reynolds numbers between 9×106 and 15×106 and for waviness profiles with different ranges of wavelengths. Finally, some additional studies are presented for different angles of attack and Mach numbers to show their effects on the computed tolerances. Graphic abstract: (Figure presented.).

© The Author(s), 2024. Published by Cambridge University Press.Large-eddy simulations of a flat-plate boundary layer, without a leading edge, subject to multiple levels of incoming free-stream turbulence are considered in the present work. Within an input–output model, where nonlinear terms of the incompressible Navier–Stokes equations are treated as an external forcing, we manage to separate inputs related to perturbations coming through the intake of the numerical domain, whose evolution represents a linear mechanism, and the volumetric nonlinear forcing due to triadic interactions. With these, we perform the full reconstruction of the statistics of the flow, as measured in the simulations, to quantify pairs of wavenumbers and frequencies more affected by either linear or nonlinear receptivity mechanisms. Inside the boundary layer, different wavenumbers at near-zero frequency reveal streaky structures. Those that are amplified predominantly via linear interactions with the incoming vorticity occur upstream and display transient growth, while those generated by the nonlinear forcing are the most energetic and appear in more downstream positions. The latter feature vortices growing proportionally to the laminar boundary layer thickness, along with a velocity profile that agrees with the optimal amplification obtained by linear transient growth theory. The numerical approach presented is general and could potentially be extended to any simulation for which receptivity to incoming perturbations needs to be assessed.

© 2024, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.We aim to reduce the noise emitted by high-speed turbulent jets using recently developed resolvent-based estimation and control tools. Our approach relies on detecting noise-generating wavepackets and canceling them via actuation. This paper reports on our progress toward this objective in the form of (i) implementation and validation of these resolvent-based tools in a large-scale CFD solver and (ii) preliminary estimation results for a subsonic jet. We validate our implementation via comparisons to the literature for a laminar channel flow, the acoustic response to a monopole forcing in a freestream, a trailing-line vortex problem, an airfoil wake, and resolvent modes for a jet. The preliminary estimation study for the subsonic jet shows that operator-based and data-driven versions of the methods yield similar estimation kernels and results. Future work will focus on extending this study to a series of supersonic jets and systematically exploring the selection and placement of sensors, actuators, and targets to mitigate noise-generating wavepackets most effectively

© 2024, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.We present the results from a physics-based model of the trailing-edge (TE) noise radiated by an airfoil, obtained from resolvent analysis of the turbulent mean flow. In our approach, the acoustic model input is reduced to the optimal coherent structures identified by the resolvent. This method has the advantage of isolating the main mechanisms generating noise in the turbulent flow and, unlike empirical models, is applicable to a wide variety of cases. We investigate a NACA0012 airfoil at 3 deg angle of attack, equipped with a zigzag trip to trigger a turbulent boundary layer, which results in broadband TE noise. The analysis is based on a large eddy simulation (LES) for a chord-based Reynolds number Re = 2.105 . The time-averaged flow is used to construct the linear operator underlying resolvent analysis, and a spectral proper orthogonal decomposition (SPOD) of the snapshots is used to extract the main hydrodynamic and acoustic features of the flow, used as a reference for the resolvent model. The results demonstrate that the resolvent-based model can accurately reproduce both the coherent structures associated with TE noise and the directivity of the radiated sound field when low-rank dynamics are identified with SPOD. Although the region of low-rank dynamics corresponds to the peak of acoustic power, a significant portion of the spectrum is associated with high-rank dynamics, which we do not attempt to model here. Nevertheless, the resolvent model identifies a wavepacket on the suction side of the trailing edge as the main driver of TE noise, and allows us to investigate spanwise wavenumbers which are not resolved in the LES.

© 2024, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.The dynamics of wavepackets in an elliptical jets are studied using direct numerical simulation (DNS) data of an AR = 2 incompressible elliptical jet at Reynolds number Re = 400. Analysis of the numerical data displays several complex features, the most striking being axis switching, a phenomenon that strongly affects the development of coherent structures in the flow. By applying spectral proper orthogonal decomposition (SPOD), it was found that modes in the SA symmetry were dominated by the Se1 flapping geometry in the upstream region. After the axis-switching point, the mode structure becomes more complex and multi-modal at mid-frequencies, while the mode structure remains largely unchanged for very low frequencies. Linear parabolised stability equations (PSE) are also used to evaluate the development of the different Kelvin-Helmholtz wavepackets in this elliptical jet showing excellent agreement with the SPOD modes.

© 2024, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.Upstream-travelling guided jet waves have been shown to be one of the key elements in many resonance processes underpinned in high-speed jets. Despite its importance, many of its characteristics, including how these waves are generated and how it can travel subsonically, have not been detailed in the literature. In this work, we aim to provide a clarification about the dynamics of this mode. With the aid of an acoustic scattering formulation, we are able to show that the guided-jet mode results from total-internal-reflection and transmission to decaying waves, arising from the shear layer behaving like a hard duct. After total reflection, only discrete streamwise wavenumbers may be supported by the flow, with these wavenumbers dictated by the fact that the standing wave formed inside of the jet must fit between the two shear layers. Close to the sonic line, the transmission of this mode to the outside is maximum, leading to a net-energy flux directed upstream, which dictates the direction of propagation of this mode in the eigenspectrum, providing a clear connection to the better understood soft-duct mode.

© 2024, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.The present paper is a follow up of a previous study on the effect of streaky-generating cylindrical tabs located on the inner surface of a round nozzle on jet aeroacoustics (Amaral et al., AIAA AVIATION 2023 Forum, p. 4516, 2023). The aim is to identify coherent structures through stereoscopic particle image velocimetry (stereo PIV) measurements obtained in crossstream planes parallel to the jet nozzle exit. As the tabbed nozzle has L-fold symmetry, Floquet exponents are used to perform Fourier decomposition in the azimuthal direction. Spectral proper orthogonal decomposition (SPOD) is employed to extract coherent structures. Comparison of the structures obtained for nozzles with and without tabs show the strong enhancement of streaks produced by the tabbed nozzle.

© 2024, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.In the last few years, flow control has become increasingly important for the aeronautical field, since it is seen as a promising tool to design safer and more efficient aircraft. In this regard, noise emission is still a major concern in the aviation industry. Specifically, for the under-wing configuration currently adopted in civil aircraft. When the jet interacts with a nearby surface, such as the wing, hydrodynamic structures are scattered into the acoustic field, drastically increasing the emitted noise. Within this context, a feed-forward control scheme is considered for the attenuation of jet installation noise in the far field. Since non-causality is observed in several flow control problems solved in the frequency domain, we compare a wave-cancelling approach, where causality is imposed via the truncation of the control kernel, to the Wiener-Hopf approach, where the causality constraint is imposed a priori. The latter provides an optimal causal solution, and with this, prevents the drop in performance that may be observed in flow control applications that use a truncated solution. The results presented here show a significantly better performance of the Wiener-Hopf method with respect to that of a truncated Kernel, where the control was performed based on microphones measurements, which provided the axisymmetric mode in the near field of the jet as the input signal for the controller. An attenuation of up to 5dB of the broadband spectral hump related to installation effects is obtained.

© 2024, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.Coherence decay has been understood to be a key quantity to predict acoustic noise emitted by wavepackets in subsonic turbulent jets. Frequency-domain frameworks such as input-output and resolvent analyses are able to predict accurately the spatial structure of wavepackets turbulent flows compared to coherent structures educed from simulation data (as for example identified using spectral proper orthogonal, SPOD). However, at least at reduced-order, they are unable to capture two-point statistics such as coherence. A missing piece is the modelling of variability induced by the turbulence, which jitters (disorganises) the coherent structures and leads to stronger noise radiation. The aim of the present study is to consider the impact of turbulence on jet wavepackets through stochastic modelling under location uncertainty. This framework considers the conservation of mass and momentum of fluid parcels submitted to a stochastic transport, representing here the effect of turbulence. By linearising the resulting generalised stochastic Navier–Stokes equations and expressing it in the Fourier domain, a stochastic linear model (SLM) is obtained. We explore in this paper that ability of SLM to predict the two point coherence of the wavepackets in turbulent jets, and show its impact on acoustic emissions.

© 2024, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.A current area of interest within jet noise is the installed-jet configuration, being a representation of interactions between the aircraft exhaust and the wing. This work considers a previously presented dataset (Amaral et al. AIAA paper 2023-3830) where a simplified configuration involving a round jet and a rectangular plate was studied, and explores the different tonal regimes that are observed across jet Mach number and plate radial offset (R/D) for constant plate axial offset and angle. These are, broadband, transitional, linear frequency-selection (LFS), LFS with non-linearities, and non-linear frequency-selection (NLFS). Results also suggested a transition from LFS to NLFS tone as R/D is decreased, and that for the case of NLFS, triadic interactions between two frequencies may produce all other tones within the spectrum.

© 2024, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.The aim of present work is to investigate trailing-edge noise generation mechanisms to improve prediction tools and control strategies. We focus on a NACA 0012 airfoil at 3 degrees angle of attack with zigzag tripping elements close to the leading edge to generate a turbulent boundary layer. A compressible implicit large eddy simulation (LES), using the open-source high-order numerical framework PyFR, is performed for collecting data for our analysis. For comparison, we use data from an experimental campaign performed in parallel at the facility in TU Berlin. The comparison of velocity and sound pressure statistics shows good agreement between simulations and experiments. Further, spectral proper orthogonal decomposition (SPOD) is applied to the LES dataset to investigate dominant feature of the turbulent boundary layer and its relation to sound radiation. SPOD analysis is applied to different spanwise wavenumbers in order to understand their contribution to noise generation. Leading SPOD modes for the first spanwise wavenumbers, which dominate acoustic radiation, are shown to correspond to wavepackets. The contribution of such coherent structures in the radiated sound field is examined, clarifying their contribution to trailing-edge noise for a wide range of frequencies.

© 2023 American Physical Society.A resolvent-based methodology is employed to obtain spatiotemporal estimates of turbulent pipe flow from probe measurements of wall shear-stress fluctuations. Direct numerical simulations (DNSs) and large-eddy simulations (LESs) of turbulent pipe flow at a friction Reynolds number of 550 are used as databases. We consider a DNS database as the true spatiotemporal flow field, from which wall shear-stress fluctuations are extracted and considered as measurements. A resolvent-based estimator is built following our earlier work [Amaral, J. Fluid Mech. 927, A17 (2021)0022-112010.1017/jfm.2021.764], requiring a model for the nonlinear (or forcing) terms of the Navier-Stokes equations system, which are obtained from another DNS database, as in our earlier work, and from a series of computationally cheaper LES databases with coarser grids; the underlying idea is that LESs may provide accurate statistics of nonlinear terms related to large-scale structures at a low computational cost. Comparisons between the DNS and the estimates indicate that sufficiently accurate results can be achieved with estimators built with statistics from LESs with an order of magnitude fewer grid points than the DNSs, with estimates closely matching the reference DNS results up to the buffer layer and reasonable agreement up to the beginning of the log layer.

© 2023 American Physical Society.Reactive flow control has been shown to be a promising tool to improve, among other aspects, the aerodynamic characteristics of an aircraft. This paper focuses on the use of reactive flow control to attenuate Tollmien-Schlichting (TS) waves over a wing profile. TS waves are an instability mechanism that is one of the first stages of boundary layer transition to turbulence. The Wiener-Hopf technique was used in this work for the experimental boundary layer control. The approach improves previous wave-cancellation techniques that, by constructing control kernels in the frequency domain, lead to control kernels with a noncausal part, i.e., actuation would need future sensor information to be constructed. In practical applications, it is unfeasible to access this type of information. Ignoring the noncausal part of the kernel leads to suboptimal solutions that might significantly degrade the performance of the controller. The Wiener-Hopf formalism allows us to take into account causality constraints in the formulation of the control problem, leading to an optimal realistic solution and a control kernel that is causal by construction. Moreover, it is possible to construct the control strategy based only on the power and cross-spectra obtained experimentally in a data-driven approach. The present work shows how to apply experimentally the Wiener-Hopf resolvent-based formalism using signals from a wind tunnel experiment, demonstrating that the TS waves can be effectively attenuated via a Wiener-Hopf-based controller, which yielded better results than a typical wave-cancellation approach.

© The Author(s), 2023. Published by Cambridge University Press.We present the results of direct numerical simulations of a NACA 0012 airfoil, with Mach number 0.3 and angle of attack of, examining the dynamics of the flow with increasing Reynolds numbers. Two-dimensional simulation results are obtained with chord-based Reynolds numbers in the range, where each simulation uses the last time step of the previous one as a starting point, to capture the evolution of dynamics as a function of. The development of the pressure fluctuations with time shows a transition from periodic to quasi-periodic attractor for, leading to the emergence of secondary tones in the wall and acoustic field pressure spectra, different from peaks related to the fundamental frequency and the respective harmonics; a second, incommensurate frequency appears, leading to several secondary tones with frequency, with and integers. Further increase of the Reynolds number leads to the emergence of a tertiary frequency, indicating a route to chaos of the Ruelle-Takens-Newhouse type. Such a mechanism is related to the ladder-type characteristic structure of the tones, indicating that dynamic systems theory is an important tool for understanding airfoil tonal noise.

© 2023 by the American Institute of Aeronautics and Astronautics, Inc..In this work, a kinematic wave-packet model is used to predict installed-jet noise. Large-eddy simulation results of freejets, for Mach numbers 0.4 and 0.9, are used to obtain parameters of wave packets representing large-scale turbulent structures, which were used to provide a model source for the Lighthill analogy used to predict far-field noise spectra. The source amplitude in the model is calibrated using noise measurements for a freejet, and such a wave-packet source is used to predict noise of the same jet in an installed configuration using a tailored Green’s function. Results from the prediction model are compared to installed-jet experimental data for four different observer positions and a large range of frequencies. Overall, the model predicts both directivities and amplitudes similar to the experimental data, with a hump in the generated noise for lower Strouhal numbers and a clear peak near a Strouhal number of 0.2. This low-order model is fast and flexible, and it is expected to be helpful in preliminary aircraft design.

© 2023 American Physical Society. Stochastic linear modeling proposed in Tissot, Mémin, and Cavalieri [J. Fluid Mech. 912, A51 (2021)0022-112010.1017/jfm.2020.1168] is based on classical conservation laws subject to a stochastic transport. Once linearized around the mean flow and expressed in the Fourier domain, the model has proven its efficiency to predict the structure of the streaks of streamwise velocity in turbulent channel flows. It has been in particular demonstrated that the stochastic transport by unresolved incoherent turbulence allows us to better reproduce the streaks through lift-up mechanism. In the present paper, we focus on the study of streamwise-elongated structures, energetic in the buffer and logarithmic layers. In the buffer layer, elongated streamwise vortices, named rolls, are seen to result from coherent wave-wave nonlinear interactions, which have been neglected in the stochastic linear framework. We propose a way to account for the effect of these interactions in the stochastic model by introducing a stochastic forcing, which replaces the missing nonlinear terms. In addition, we propose an iterative strategy in order to ensure that the stochastic noise is decorrelated from the solution, as prescribed by the modeling hypotheses. We explore the prediction abilities of this more complete model in the buffer and logarithmic layers of channel flows at Reτ=180, Reτ=550, and Reτ=1000. We show an improvement of predictions compared to resolvent analysis with eddy viscosity, especially in the logarithmic layer.

© 2022, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.Colistin remains one of the few available options for the treatment of infections caused by resistant bacteria. Pharmacokinetic (PK) studies have been successful in estimating the appropriate colistin methanesulfonate (CMS) dose to achieve a target colistin concentration. Currently, there is a consensus that the dose of CMS should vary according to the patient renal function since CMS is mainly eliminated by renal route. For this same reason, the loading dose should vary according to the patient's renal capacity; however, this is not the current clinical practice. In this study we develop a framework to determine two key parameters for the loading dose regimen: (1) the optimal dose according to the characteristics (renal function and weight) of the patient; (2) the waiting time before the maintenance dose. Based on a previous PK model, our framework allows a fast parameter sweep so as to select optimal loading dose and waiting time minimizing the deviation between the plasma concentration and a target value. The results showed that patients presenting low creatinine clearance (CrCL) should receive a lower CMS loading dose with longer interval to start maintenance treatment to avoid nephrotoxic colistin concentrations. In cases of high CrCL, the dose should be higher and the interval to the next dose shorter to avoid subtherapeutic concentrations. Optimization of the loading dose should considerably improve colistin therapy, as the target concentration is reached more quickly, without reaching toxic values.

© 2023, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.In recent years, flow control has become increasingly important for the aeronautical field, as it is seen as a promising tool to design safer, quieter and more efficient aircraft. Since non-causality is observed in several flow control problems solved in the frequency domain, we consider here the use of the Wiener-Hopf technique for the control of a forced turbulent jet. Such approach allows us to enforce causality when obtaining the control kernel, which provides an optimal causal solution, and with this, prevents the drop in performance that may be observed in flow control applications that use a truncated solution. The experimental results presented here shows a significantly better performance of the Wiener-Hopf method with respect to that of a truncated kernel obtained using a wave-cancellation approach.

© 2023, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.Large-eddy simulations of a Blasius boundary layer over a flat plate, without a leading edge, at multiple levels of incoming free stream turbulence are considered. The data from the saved snapshots are then applied to an input-output model where non-linear terms of the Navier-Stokes equations are treated as an external forcing. By separating the inputs corresponding to the perturbations coming through the inflow boundary and non-linear forcing, we can perform the full reconstruction of the statistics of the flow observed in the simulations and discriminate which frequencies and wavenumbers are more affected by either linear or non-linear dynamics. Different frequency-wavenumber combinations reveal streaks that grow predominantly through linear or non-linear mechanisms, the former occurring upstream and the latter at downstream stations of the boundary layer.

© 2023, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.This paper reports aeroacoustic experiments on round jets containing tab elements adhered to the nozzle internal surface with the purpose of generating steady streaks in the nozzle boundary-layer. Such streaks are theoretically expected to reduce growth rates associated with the Kelvin-Helmholtz mechanism and, in turn, to reduce jet noise. Nozzle configurations with and without a boundary-layer transition trigger element (carborundum trip), were studied. Stereo particle image velocimetry (stereo PIV) was employed to measure the three components of the velocity for a series of planes parallel to the nozzle exit at Mj = 0.7 in the 0.03 xD 10 streamwise range, where x is the streamwise distance and D is the jet diameter. Such measurements clearly show alternating regions of high and low speed flow due to the streaks that were induced by the tabs on the nozzle boundary-layer and are sustained in the jet shear-layer up to at least xD = 3. The acoustic experiments were performed in an anechoic facility, using an azimuthal array containing 18 equally-spaced microphones to characterize the acoustic field. The antenna was employed to conduct measurements at 15 streamwise stations in the 20 deg θ 90 deg polar range. All acoustic experiments were conducted in the 0.4 Mj 0.9 Mach number range. The presence of the tab elements leads to noise reductions of up to 6 dB/St, observed for Strouhal numbers in the 0.1 St 0.5 range, Mj = 0.4, axisymmetric azimuthal mode and untripped boundary-layer case. When the trip mechanism is present, the noise reduction is up to 3 dB/St. An overall sound pressure level (OASPL) reduction of up to 3 dB was measured for axisymmetric mode of the tabbed case for Mj = 0.4. As the tabs were designed based on boundary-layer measurements at Mj = 0.4, the noise reduction decreases with increasing Mach number. Nevertheless, significant noise reductions of up to 1.5 dB are still observed up to Mj = 0.9 and axisymmetric mode. Moreover, the noise reduction is up to 6 dB for the two first helical modes. The noise reduction was measured at both lower and higher polar angles and for almost the entire frequency range, up to at least St 2. Streak-inducing devices such as the present tabs are thus a promising approach to reduce jet noise

© 2023, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.In a combined experimental and numerical effort we investigate aerofoil tonal noise generation and reduction. The means of noise control are streak generators in form of cylindrical roughness elements. These elements are placed periodically along the span of aerofoil at the mid chord streamwise position. Experiments are performed for a wide range of Reynolds number and angle of attack. In the present work we concentrate on our numerical investigations. We have performed wall-resolved large-eddy simulations for a given angle of attack of 0 degree and Mach 0.3. Two Reynolds numbers 0.8 × 105 and 1.0 × 105 have been investigated, showing acoustic results consistent with experiments at the same Reynolds but lower Mach numbers. Roughness elements attenuate tones in the acoustic field, and, for the higher Reynolds number, suppress them. Through Fourier decomposition and POD analysis of streamwise velocity data, dominating structures have been identified. Further, the coupling between structures generated by surface roughness and instability modes (Kelvin-Helmholtz) of shear layer has been identified, suggesting stabilisation mechanisms by which the sound generation by the airfoil is reduced by the roughness elements.

© 2023, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.This experimental work investigates the trailing-edge (TE) noise from a NACA0012 airfoil in an open-jet wind tunnel, for chord-Reynolds numbers between 105 and 4.6 × 105 and angles of attack between 0° and 6°. The range of parameters for which TE noise is either tonal or broadband in the present experiments is in good agreement with existing literature results. One of the main objectives of this work is to test the assumption of recent modelling approaches based on the linearised Navier-Stokes operator. These studies focus on spanwise coherent structures in the turbulent boundary layer to investigate the mechanisms responsible for trailing edge noise, as they always satisfy the trailing edge scattering condition. However, numerical simulations routinely use a narrow numerical domain and periodic lateral boundary conditions, which could favour spanwise coherent dynamics. Therefore, particular emphasis is placed on the experimental characterisation of the spanwise wavenumber content of the pressure fluctuations on the airfoil surface and in the acoustic field. A good agreement with theoretical and numerical observations is found, as the spanwise wavenumber contents of the acoustic field are in good agreement with the edge scattering condition. Furthermore, the coherence between the surface pressure fluctuations and the acoustic fields is significantly improved when considering spanwise-coherent structures by spanwise averaging of the temporal signals, even in the case of broadband noise.

© 2023, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.An array of cylindrical roughness elements was used to reduce the tonal noise introduced by the separation bubble over a NACA 0012 airfoil at low angles of attack. Experiments were performed for four configurations: a baseline smooth airfoils, two with roughness elements at only one of the airfoil surfaces (pressure side or suction side), and the other with roughness elements at both airfoil surfaces. Arowof spanwise periodically spaced cylinderswas placed close to the mid-chord position in order to induce streaks that render the bubble three-dimensional, decreasing separation and stabilizing the Kelvin-Helmholtz instability of the separated shear layer, which is related to tonal noise. Our results show a decrease, and in some cases the total suppression, of the tonal noise at Reynolds numbers ranging from 0.6×105 to 2.5×105, and angles of attack ranging from 0 to 4 degrees.

© 2023 Elsevier Masson SAS. All rights reserved.An attempt to improve the accuracy of resolvent-based predictions by including velocity correlations in the linear model is developed here. Closure assumptions for unresolved nonlinearities are thus pushed back to a higher order. Turbulent channel flow is considered as a test case: response and forcing modes obtained from singular value decomposition of the new resolvent model are compared to Spectral Proper Orthogonal Decomposition (SPOD) modes extracted from a Direct Numerical Simulation (DNS) database. The performance of the approach is also measured against previous resolvent-based models. The new model does not yield significant global improvement, but does improve predictions in some regions. Further work on the method should target the linear modeling of the velocity-pressure gradient correlation tensor.

© Spectral proper orthogonal decomposition (SPOD) is an increasingly popular modal analysis method in the field of fluid dynamics due to its specific properties: a linear system forced with white noise should have SPOD modes identical to response modes from resolvent analysis. The SPOD, coupled with the Welch method for spectral estimation, may require long time-resolved datasets. In this work, a linearised Ginzburg-Landau model is considered in order to study the method's convergence. Spectral proper orthogonal decomposition modes of the white-noise forced equation are computed and compared with corresponding response resolvent modes. The quantified error is shown to be related to the time length of Welch blocks (spectral window size) normalised by a convective time. Subsequently, an algorithm based on a temporal data shift is devised to further improve SPOD convergence and is applied to the Ginzburg-Landau system. Next, its efficacy is demonstrated in a numerical database of a boundary layer subject to bypass transition. The proposed approach achieves substantial improvement in mode convergence with smaller spectral window sizes with respect to the standard method. Furthermore, SPOD modes display growing wall-normal and spanwise velocity components along the streamwise direction, a feature which had not yet been observed and is also predicted by a global resolvent calculation. The shifting algorithm for the SPOD opens the possibility for using the method on datasets with time series of moderate duration, often produced by large simulations.

© 2022 American Physical Society.Reduced-order models were derived for plane Couette flow using Galerkin projection, with orthonormal basis functions taken as the leading controllability modes of the linearized Navier-Stokes system for a few low wave numbers. Resulting Galerkin systems comprise ordinary differential equations, with a number of degrees of freedom ranging from 144 to 600, which may be integrated to large times without any indication of numerical instability. The reduced-order models so obtained are also found to match statistics of direct numerical simulations at Reynolds number 500 and 1200 with reasonable accuracy, despite a truncation of orders of magnitude in the degrees of freedom of the system. The present models offer thus an interesting compromise between simplicity and accuracy in a canonical wall-bounded flow, with relatively few modes representing coherent structures in the flow and their dominant dynamics.

© 2022 authors. Published by the American Physical Society.Resolvent analysis has found applications in several areas of fluid mechanics, providing physical insight into both laminar and turbulent flows. In spite of such fact, the global (3D) resolvent is computationally expensive, which limits the size of the domain and the Reynolds number of the flows which can be considered. In this work, we derive a parabolic resolvent approach, which enables a significant increase in the computational efficiency of the calculation, for streaky structures in boundary layer flows. The computational speedup depends on the size of the problem and could be of more than one order of magnitude for the same accuracy as the global calculation. The method is derived based on an optimization method via the Lagrange multipliers over the linearized boundary layer equations and it is coupled to a Krylov-Arnoldi decomposition to the computation of suboptimals. The application of the method is exemplified for two problems: A Falkner-Skan boundary layer, where we obtain trends for both the optimals and suboptimals, and a turbulent boundary layer, where characteristics such as the double peak in the spectrum and the characteristic inner and outer length scales can be recovered when a variable eddy viscosity is considered. In both cases, a scaling is found for the dominant gain, given in terms of the fourth power of the Reynolds number, defined in terms of the relevant scale for the problem, the displacement thickness, and the modified Rotta-Clauser parameter for the laminar and turbulent boundary layers, respectively. For the laminar case, we further demonstrate that a forcing limited to the free-stream region is capable of generating streaky structures inside the boundary layer, a relevant feature for free-stream turbulence-induced transition.

© Self-similarity of wall-attached coherent structures in a turbulent channel at is explored by means of resolvent analysis. In this modelling framework, coherent structures are understood to arise as a response of the linearised mean-flow operator to generalised frequency-dependent Reynolds stresses, considered to act as an endogenous forcing. We assess the self-similarity of both the wall-attached flow structures and the associated forcing. The former are educed from direct numerical simulation data by finding the flow field correlated with the wall shear, whereas the latter is identified using a frequency space version of extended proper orthogonal decomposition (Borée, Exp. Fluids, vol. 35, issue 2, 2003, pp. 188-192). The forcing structures identified are compared to those obtained using the resolvent-based estimation introduced by Towne et al. (J. Fluid Mech., vol. 883, 2020, A17). The analysis reveals self-similarity of both wall-attached structures - in quantitative agreement with Townsend's hypothesis of self-similar attached eddies - and the underlying forcing, at least in certain components.

© The Author(s), 2022.The publisher apologises that upon publication of the article Martini, E., Jung, J., Cavalieri, A., Jordan, P. & Towne, A. (2022), two author affiliations were switched around. The full and correct author affiliations are: Eduardo Martini1,2, Junoh Jung3, André V.G. Cavalieri1, Peter Jordan2 and Aaron Towne3 1Instituto Tecnológico de Aeronáutica, 12228-900 São José dos Campos/SP, Brazil 2Département Fluides, Thermique et Combustion, Institut Pprime, CNRS, Université de Poitiers, ENSMA, 86000 Poitiers, France 3University of Michigan, Ann Arbor, MI 48109, USA The online version of this article has been updated.

© The Author(s), 2022. Published by Cambridge University PressThe application of control tools to complex flows frequently requires approximations, such as reduced-order models and/or simplified forcing assumptions, where these may be considered low rank or defined in terms of simplified statistics (e.g. white noise). In this work we propose a resolvent-based control methodology with causality imposed via a Wiener-Hopf formalism. Linear optimal causal estimation and control laws are obtained directly from full-rank, globally stable systems with arbitrary disturbance statistics, circumventing many drawbacks of alternative methods. We use efficient, matrix-free methods to construct the matrix Wiener-Hopf problem, and we implement a tailored method to solve the problem numerically. The approach naturally handles forcing terms with space-time colour; it allows inexpensive parametric investigation of sensor/actuator placement in scenarios where disturbances/targets are low rank; it is directly applicable to complex flows disturbed by high-rank forcing; it has lower cost in comparison to standard methods; it can be used in scenarios where an adjoint solver is not available; or it can be based exclusively on experimental data. The method is particularly well suited for the control of amplifier flows, for which optimal control approaches are typically robust. Validation of the approach is performed using the linearized Ginzburg-Landau equation. Flow over a backward-facing step perturbed by high-rank forcing is then considered. Sensor and actuator placement are investigated for this case, and we show that while the flow response downstream of the step is dominated by the Kelvin-Helmholtz mechanism, it has a complex, high-rank receptivity to incoming upstream perturbations, requiring multiple sensors for control.

© 2022 American Physical Society.This paper presents a study on wave cancellation in forced jets. Building on recent work on real-time control of forced turbulent jets by Maia et al. [Phys. Rev. Fluids 6, 123901 (2021)10.1103/PhysRevFluids.6.123901], we here assess the effect of jet upstream conditions and nonlinearity on wave-cancellation performance. The experiments are performed in jets with laminar and turbulent boundary layers inside the nozzle. An open-loop campaign is first conducted, in which the goal is to analyze the jet response to stochastic forcing with variable bandwidth. The upstream conditions of the jet are found to have a strong influence on the jet response. For narrow forcing bandwidths, both jets present a clear response regime. However, in the initially laminar jet, as bandwidth is increased, high growth rates and transition to turbulence in the initial region underpin the onset of nonlinear effects in jet response. In the initially turbulent jet, on the other hand, lower growth rates allow a linear response regime to be maintained for a broader range of forcing parameters. As the wave cancellation strategy is linear, reactive control is found to be more effective in the initially turbulent jet, consistent with the results of the open-loop analysis.

© 2021 The Author(s). Published by Cambridge University Press.The present work studies the nonlinear dynamics of a shear layer, driven by a body force and confined between parallel walls, a simplified setting to study transitional and turbulent shear layers. It was introduced by Nogueira & Cavalieri (J. Fluid Mech., vol. 907, 2021, A32), and is here studied using a reduced-order model based on a Galerkin projection of the Navier-Stokes system. By considering a confined shear layer with free-slip boundary conditions on the walls, periodic boundary conditions in streamwise and spanwise directions may be used, simplifying the system and enabling the use of methods of dynamical systems theory. A basis of eight modes is used in the Galerkin projection, representing the mean flow, Kelvin-Helmholtz vortices, rolls, streaks and oblique waves, structures observed in the cited work, and also present in shear layers and jets. A dynamical system is obtained, and its transition to chaos is studied. Increasing Reynolds number leads to pitchfork and Hopf bifurcations, and the latter leads to a limit cycle with amplitude modulation of vortices, as in the direct numerical simulations by Nogueira & Cavalieri. Further increase of leads to the appearance of a chaotic saddle, followed by the emergence of quasi-periodic and chaotic attractors. The chaotic attractors suffer a merging crisis for higher, leading to a chaotic dynamics with amplitude modulation and phase jumps of vortices. This is reminiscent of observations of coherent structures in turbulent jets, suggesting that the model represents a dynamics consistent with features of shear layers and jets.

© The Author(s), 2021. Published by Cambridge University Press.We present an analysis of the linear stability characteristics of shock-containing jets. The flow is linearised around a spatially periodic mean, which acts as a surrogate for a mean flow with a shock-cell structure, leading to a set of partial differential equations with periodic coefficients in space. Disturbances are written using the Floquet ansatz and Fourier modes in the streamwise direction, leading to an eigenvalue problem for the Floquet exponent. The characteristics of the solution are directly compared with the locally parallel case, and some of the features are similar. The inclusion of periodicity induces minor changes in the growth rate and phase velocity of the relevant modes for small shock amplitudes. On the other hand, the eigenfunctions are now subject to modulation related to the periodicity of the flow. Analysis of the spatiooral growth rates led to the identification of a saddle point between the Kelvin-Helmholtz mode and the guided jet mode, characterising an absolute instability mechanism. Frequencies and mode shapes related to the saddle points for two conditions (associated with axisymmetric and helical modes) are compared with screech frequencies and the most energetic coherent structures of screeching jets, resulting in a good agreement for both. The analysis shows that a periodic shock-cell structure has an impulse response that grows upstream, leading to oscillator behaviour. The results suggest that screech can occur in the absence of a nozzle, and that the upstream reflection condition is not essential for screech frequency selection. Connections to previous models are also discussed.

© 2022 12th International Symposium on Turbulence and Shear Flow Phenomena, TSFP 2022. All rights reserved.A resolvent-based methodology is employed to obtain non-causal spatio-temporal estimates of turbulent pipe flow from low-rank probe measurements of wall shear-stress fluctuations. DNS and LES pipe flow numerical simulations at friction Reynolds number of 550 are used as databases. We consider one of the DNS databases as the true spatio-temporal flow field, from which the low-rank measurements are extracted. Such database is also employed to verify the accuracy of the linear estimators. The estimator needs a model for the nonlinear (or forcing) terms of the Navier-Stokes equations system, which are obtained from a DNS database and from a series of computationally cheaper LES databases with grids coarser than the DNS. Comparisons between the reference DNS and the estimates indicate that sufficiently accurate results can be achieved with cheaper LES containing up to 10% of the number of grid points of the DNS, with estimates closely matching the reference DNS results up to the buffer-layer and reasonable agreement up to the beginning of the log layer.

© 2022 12th International Symposium on Turbulence and Shear Flow Phenomena, TSFP 2022. All rights reserved.Coherent structures are found in many different turbulent flows, and they are known to drive self-sustaining processes in minimal-unit turbulence. Identifying the triadic interactions between coherent structures can provide insights beyond what is possible in the framework of linearised models. There are infinite possible interactions that may generate a given structure, and thus a method to systematically study those, ranking them in terms of their contribution, is of interest. We here use the resolvent-based extended spectral proper orthogonal decomposition (RESPOD) approach (Karban, U. et al. 2022 Self-similar mechanisms in wall turbulence studied using resolvent analysis. Journal of Fluid Mechanics 969, A36) to identify the relevant triadic interactions for a minimal Couette flow at Reτ = 34, studying the interactions that give rise to wall-attached structures, obtained by measuring the wall-shear. Our analysis reveals that there are six triadic interactions that dominate the most-energetic wall-attached structure.

© 2022 12th International Symposium on Turbulence and Shear Flow Phenomena, TSFP 2022. All rights reserved.We propose a formulation to study the effect of streaks in the spatial development of wavepackets. To this end, a modified version of the parabolised stability equations (PSE) linearized around a streak-containing mean flow is used, which considers a series of azimuthal wavenumbers in the solution. In the present case, streaks are obtained from experiments using spectral proper orthogonal decomposition applied to particle image velocimetry data, and extrapolated in the radial direction using a Gaussian fit. Streaks and rolls predicted by resolvent analysis are also used in the analysis to evaluate the effect of streamwise vortices in the development of the noise-generating structures. Results show that streaks non-trivially modify the spatial support of the Kelvin-Helmholtz wavepackets and their phase velocity, which may lead to changes in the sound generation efficiency of the jet. New structures across the shear layer induced by the presence of streaks are also observed further downstream for high streak amplitudes.

© 2022, AIAA International. All rights reserved.The present work is dedicated to the modeling of the low-frequency part of the jet installation noise (JIN) in flight conditions. It is known that the properties of JIN can be predicted based on the characteristics of the near field of an isolated jet. Unlike the static case, in the presence of a coflow, it is difficult to directly measure the structure of the pressure perturbations in the jet near field. To overcome this problem, we propose a technique based on hot-wire measurements on the jet axis, suitable both for static and flight conditions. The well-known agreement between a parabolized stability equations (PSEs) model and experimentally measured velocity fluctuations on the jet axis allows using the PSE approach for the reconstruction of the axisymmetric pressure fluctuations in the vicinity of the wing trailing-edge location. The first helical mode, which is also important for the jet installation noise prediction, is approximately reconstructed based on the fact that its properties are close to those of the axisymmetric mode. These pressure characteristics are then used as input in an analytical jet installation noise model. To confirm this approach, acoustic measurements of JIN in static and flight conditions are conducted for a laboratory subsonic jet installed near a flat plate simulating a wing. It is shown that the analytical model informed by the PSE-reconstructed pressure field is capable of capturing the main features of the low-frequency jet–plate interaction noise both in static conditions and in the presence of coflow.

© 2022, AIAA International. All rights reserved.The effect of addition of viscoelastic plies on the acoustic scattering quadrupoles near the trailing edge of laminated plates is evaluated. A numerical method is applied to compute the acoustic field scattered by finite flexible plates. For a two-dimensional problem whereby a cantilevered plate scatters sound from a point quadrupole near the free edge, results show that adding viscoelastic layers to a composite plate can modify the far-field sound. Parametric investigations show that this treatment reduces scattered noise near resonance frequencies. Discussions on the positioning and thickness of the viscoelastic layers and operating temperature are provided. The use of outer viscoelastic layers in composite plates is predicted to significantly reduce acoustic scattering near resonances due to structural damping.

© 2025 Elsevier Masson SASA simplified integrated model of the flight dynamics of flexible aircraft is developed using the Rayleigh-Ritz and quasi-steady vortex-lattice methods. In a novel approach, the Rayleigh-Ritz method is applied to all structural components with the inclusion of six rigid-body shape functions per component, allowing the enforcement of compatibility conditions between components and the calculation of modes of vibration for the entire aircraft at once. Another novelty is that, although aerodynamic influence coefficient matrices are calculated only for the jig shape, the vortex-lattice method boundary conditions and force equations are implemented in vector form and updated throughout flight simulations, allowing the formulation to capture important nonlinear aerodynamic effects related, e.g., to angular velocities, follower forces due to wing dihedral deformation, and induced drag. The equations of motion consider mean axes and a set of unrestrained modes of vibration. For simplicity, beam-like components with small deformations are considered. Using quasi-steady aerodynamics avoids the greater unsteady aerodynamic model preparation effort and computational cost. These characteristics make the proposed integrated model potentially useful in the initial stages of aircraft design when unifying aeroelasticity and flight dynamics is mandatory, as is the case for next-generation commercial aircraft. Convergence in the Rayleigh-Ritz method is achieved by varying the number of shape functions and its application to an aircraft comprising 20 beams shows that, compared to a model with 3006 degrees of freedom, one with only 606 results in frequency errors of less than 4% for all modes below 25 Hertz. Applying the framework to aircraft with decreasing stiffness levels reveals important phenomena, such as reduced short-period mode damping and frequency, increased damping of wing bending aeroelastic modes, and increased susceptibility to aileron roll control reversal.

© 2025, American Institute of Aeronautics and Astronautics, Inc. All rights reserved.This paper explores control alternatives for a generic fighter jet focusing on handling qualities enhancement in the transonic flight regime. The aerodynamic coefficients of the aircraft exhibit abrupt variations due to shock wave interference, so nonlinear control strategies are suggested. MATLAB simulations are employed to analyze the influence of these control laws on aircraft dynamics, including automated routines for equilibrium calculations, linearization, and the design of a conventional gain-scheduled Stability Augmentation System (SAS). Preliminary results demonstrate the SAS’s lack of effectiveness in mitigating transonic nonlinearities when sensor measurement errors occur. Therefore, the application of two nonlinear control techniques is proposed and investigated: Nonlinear Dynamic Inversion (NDI) and an output based Incremental Nonlinear Dynamic Inversion (INDI). The controlled variable of the flight control system is selected based on analysis of the Zero Dynamics Matrix calculated for load factor at the pilot’s station, the C-star parameter, and a combination of C-star, true airspeed, and altitude. Whereas NDI and INDI techniques result in adequate performance and stability characteristics in nominal conditions, the INDI controller is confirmed to be more robust to sensor measurement errors.

© 2024 International Forum on Aeroelasticity and Structural Dynamics, IFASD 2024. All rights reserved.The renaissance of neural networks in the scientific community in recent years has brought new perspectives for improving the computational efficiency of traditional modeling techniques. Hamiltonian neural networks leverage the energy-preserving properties of the Hamiltonian formalism to provide surrogate models with increased interpretability compared to conventional feed-forward models. In this study, we employ a lumped-mass multibody method to derive the equations of motion of two highly flexible structures. We perform a model order reduction via modal decomposition while preserving the nonlinearities with the use of exact kinematic relations. After validating full- and reduced-order models, we use them to produce datasets and train the neural networks, which serve as ready-to-use surrogate models. Preliminary findings show that the surrogate models based on neural networks can significantly reduce the time necessary to simulate the free response of the structures. Furthermore, we demonstrate that surrogate models based on Hamiltonian neural networks have energy-preserving capabilities, maintaining accuracy levels even for long simulations. Due to their architecture, when external loads are considered, the surrogate models require the analytical calculation of the generalized forces, jeopardizing the efficiency gains obtained by our approach. We also present initial findings on the use of neural networks for faster aerodynamic models for flexible aircraft, particularly as surrogate models for the vortex-lattice method. By using a neural network as the aerodynamic surrogate model in a specific flexible aircraft simulation framework, the computational costs were reduced by a factor of 100 on average. The outcomes of this study demonstrate that surrogate models based on neural networks can soon become an efficient and reliable alternative for modeling arbitrarily flexible aircraft, provided the current limitations are addressed.

© 2021 by Antônio B. Guimarães Neto, Guilherme C. Barbosa, Juliano A. Paulino, Rafael M. Bertolin, Jéssica S. M. Nunes, Pedro J. González, Flávio L. Cardoso-Ribeiro, Maurício A. V. Morales, Roberto G. A. da Silva, Flávio L. S. Bussamra, Flávio J. Silvestre, Fernando J. O. Moreira, and Carlos E. S. Cesnik. Published by the American Institute of Aeronautics and Astronautics,.The challenges of modeling flexible aircraft include appropriate fidelity capturing and validation with experimental data. In fact, the validation of formulations and models for the flexible flight dynamics is indispensable to ensure that all the important phenomena are correctly captured. With this objective, two high-aspect-ratio flexible aircraft have been flight-tested, and coupled aeroelastic–flight dynamics data have been collected to support model validation. Additional ground vibration and static tests were carried out to fully characterize the structural dynamic properties. Numerical models were built based on a linear structural representation but with geometrically nonlinear aerodynamics. Low Reynolds number effects were included in a simplified way with lookup tables of two-dimensional airfoil data. Wing-tip effects were considered via the vortex-and doublet-lattice methods. Propulsive data were obtained with wind-tunnel tests. This paper describes the numerical models, the two aircraft, and their instrumentation and presents the data collected from the aircraft sensors during flight tests. Numerical and experimental results are compared for angular velocities, accelerations, and strains measured at different points of the aircraft. Despite its limitations and simplifications, the numerical model captures the real aircraft main aeroelastic and flight dynamic behaviors.

© 2022 by the authors. and Astronautics, Inc.,.Control law design for flexible aircraft with coupled flight and structural dynamics is currently a challenge. If not correctly addressed during control law design, the aeroservoelastic coupling can negatively affect the lateral-directional stability of the aircraft. In this context, this paper describes a methodology for the design of a stability augmentation system for the Instituto Tecnológico de Aeronáutica X-HALE flexible aircraft and proposes a performance index for numerical optimization of the closed-loop feedback gains. Comparisons between open-loop and closed-loop numerical simulation results show how the proposed control system attenuates the Dutch-roll response. An aeroservoelastic analysis is made in which it its demonstrated that the control system has small but beneficial effects on aeroelastic stability. Finally, experimental data obtained via flight tests with the real aircraft demonstrate the effectiveness of the control system in practice.

© The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature 2025.This study presents the fabrication and optimization of ultrathin silver (Ag) films by low-power DC magnetron sputtering for surface-enhanced Raman spectroscopy (SERS) applications, with emphasis on the synergistic roles of electromagnetic (EM) and chemical enhancement (CE) mechanisms. Ag nanostructures were deposited onto glass substrates with controlled deposition durations (10–300 s), enabling the formation of tunable morphologies ranging from isolated nanoparticles to quasi-continuous nanostructured films. Structural and optical analyses revealed that an ~ 8.2 nm-thick Ag film exhibits optimal SERS performance due to its interconnected architecture, high surface asymmetry, and enhanced plasmonic coupling. SERS measurements were conducted using two cationic dyes—Rhodamine 6G (R6G) and Rhodamine B (RhB)—selected for their well-characterized Raman signatures and distinct surface adsorption behaviors. The optimized Ag substrate achieved enhancement factors in the range of 10⁶–10⁹ and detection limits down to 7 × 10⁻12M. Wavelength-dependent experiments using 532 nm and 633 nm excitation revealed strong SERS responses at both wavelengths, with maximal enhancement observed at 633 nm due to superior resonance alignment with the localized surface plasmon modes of the film. Electromagnetic field estimations based on UV–Vis absorbance correlated well with experimental trends, confirming EM as the dominant mechanism. Nonetheless, energy-level alignment between the Ag Fermi level and the molecular orbitals of the dyes, particularly for R6G, supports a secondary contribution from CE, driven by charge-transfer interactions and electrostatic adsorption. These findings demonstrate that the concurrent optimization of nanostructure, plasmonic response, and analyte–surface interaction is essential for enhancing both EM and CE effects. The substrate also enabled detection of Escherichia coli, underscoring its potential for biosensing at ultra-trace levels.

© 2025 Elsevier LtdThis study investigates the influence of thickness on the structure and morphology of sputtered wurtzite GaN thin films and evaluates their potential as piezoelectric materials for surface acoustic wave (SAW) devices. High-quality GaN films were deposited on Si(100) and glass substrates via reactive magnetron sputtering under optimized conditions. X-ray diffractometry (XRD), Raman spectroscopy, and transmission electron microscopy (TEM) analysis confirmed a preferential c-axis orientation. A detailed assessment of the crystalline quality and structural properties revealed that films grown for 6 h on Si substrates exhibited superior crystallinity and lower defect density. However, increasing film thickness led to higher surface roughness, which may impact SAW device performance. These findings highlight the viability of sputtered GaN films for SAW applications, provided that deposition parameters are carefully controlled to balance crystallinity and surface roughness. This work demonstrates the potential of cost-effective sputtering technique for producing GaN films suitable for high-frequency SAW devices.

© 2025 The Authors. Published by American Chemical SocietyAtomic layer deposition (ALD) enables simultaneous passivation of silver and nanometer-scale tuning of the near-field landscape that controls surface-enhanced Raman scattering (SERS) and metal-enhanced fluorescence (MEF). Here, sputtered ∼16 nm Ag films were conformally coated with 1–20 ALD cycles of Al2O3(≈0.17–1.76 nm) and analyzed by atomic force microscopy (AFM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), spectroscopic ellipsometry, UV–Vis spectroscopy, time-resolved fluorescence, large-area Raman mapping of Rhodamine 6G and finite-difference time-domain (FDTD) modeling. Morphology evolves from isolated oxide nuclei after one cycle through a conformal roughness-amplifying shell at 5–15 cycles to vertically elongated outgrowths at 20 cycles; ellipsometry confirms self-limiting growth with 0.10 ± 0.02 nm cycle–1. Optical measurements reveal three thickness regimes: ≤1 cycle (<0.2 nm) yields SERS-dominated behavior with picosecond quenching and intense Raman hotspots; ∼5 cycles (∼0.5 nm) provides the hybrid optimum, giving the highest Raman enhancement (EF ≈ 2 × 103) together with a 4-fold fluorescence-lifetime extension (⟨τ⟩ ≈ 26 ns) that signals strong MEF; whereas >10 cycles (>1 nm) attenuate both SERS and MEF as the evanescent field decays. FDTD maps based on AFM topographies reproduce the heavy-tailed hotspot distribution and identify the 0.5–1.0 nm window as the sweet spot for co-optimizing field confinement and radiative efficiency. Stability tests show that five-cycle coatings endure solvent rinsing and cotton-swab abrasion while retaining─or even increasing─SERS activity, whereas thicker oxides guarantee mechanical integrity at the cost of weaker near-fields. These combined results show an experimentally validated framework for engineering reusable, dual-mode plasmonic substrates by angstrom-level control of dielectric spacer thickness.

© 2024 by the authors.This study investigates the high-pressure structural and vibrational properties of nano-Sc2O3 using a combination of X-ray diffraction, Raman spectroscopy, and theoretical calculations. Nano-Sc2O3 maintains its cubic bixbyite structure up to 26.4 GPa, without evidence of phase transitions, contrasting with bulk Sc2O3, which transitions to a monoclinic phase around 25–28 GPa. Raman spectroscopy reveals a pressure-induced blue shift in the vibrational modes, indicating lattice compression, and the absence of new modes confirms the retention of the cubic symmetry. Theoretical predictions using density functional theory (DFT) closely match the experimental data, validating the computational approach we use to model the pressure-dependent vibrational behavior of nano-Sc2O3. Comparisons with previous studies seem to show that the nanoscale material exhibits enhanced structural stability compared to its bulk counterpart, likely due to size effects and surface energy contributions. These findings provide new insights into the behavior of nanomaterials under extreme conditions and highlight the potential applications of nano-Sc2O3 in high-pressure environments.

© 2024 by the authors.We report a joint high-pressure experimental and theoretical study of the structural, vibrational, and photoluminescent properties of pure and Eu3+-doped cubic Y2O3 nanoparticles with two very different average particle sizes. We compare the results of synchrotron X-ray diffraction, Raman scattering, and photoluminescence measurements in nanoparticles with ab initio density-functional simulations in bulk material with the aim to understand the influence of the average particle size on the properties of pure and doped Y2O3 nanoparticles under compression. We observe that the high-pressure phase behavior of Y2O3 nanoparticles depends on the average particle size, but in a different way to that previously reported. Nanoparticles with an average particle size of ~37 nm show the same pressure-induced phase transition sequence on upstroke and downstroke as the bulk sample; however, nanoparticles with an average particle size of ~6 nm undergo an irreversible pressure-induced amorphization above 16 GPa that is completed above 24 GPa. On downstroke, 6 nm nanoparticles likely consist of an amorphous phase.

© 1973-2012 IEEE.This study employed an inverted reactor approach to activate tap water (TW) using effluent bubbles derived from a gliding arc discharge (GAD). Optical emission spectroscopy (OES) analysis revealed the dominant presence of nitrogen species and oxygen radicals within specified spectral ranges. The physicochemical attributes of the plasma-activated TW (PATW) remained consistent, highlighting the efficacy of the reactor's bubbling system. Through UV-Vis spectrophotometry and pH analysis, the notable observation was the stabilizing influence of hydrogen peroxide (H2O2) and positive hydrogen ions (H+) during the initial activation phases (75 min), which played a significant role in maintaining mildly alkaline pH. Energy efficiency metrics demonstrated a decline up to 1.25 h of activation, with subsequent stabilization. Our research outcomes further emphasize the efficacy of GAD, shedding light on its significant potential in optimizing the water activation process.

© 2024, Escola de Minas. All rights reserved.A Hollow Cathode Plasma Enhanced Chemical Vapor Deposition (HC-PECVD) reactor was used to deposit silver doped Diamond-Like Carbon (Ag-DLC) films on Ti6Al4V alloy employing two methodologies: i) producing a silicon interlayer, using tetramethylsilane (TMS) as silicon precursor, varying the argon flow of the hollow cathode; and ii) carbonitriding the substrate. Profilometry, Raman, and Secondary Ion Mass Spectrometry (SIMS), as well as nanohardness, micro-scratch, scratch, and VDI 3198 indentation tests were used to evaluate the characteristics of the films and their adhesion on the substrates. The results demonstrated that the argon flow can be used for tuning the Ag-DLC film’s hardness, toughness, and adherence on silicon interlayers. The carbonitriding process, in turn, provided an improvement in the film toughness compared with non-carbonitrided samples. Considering the lower cost and easier handling of N2 compared to the silicon precursors commonly available (TMS, HDMSO, SiH4, etc.), the carbonitriding process proved more appropriate to improve the adhesion of the Ag-DLC films on the Ti6Al4V alloy.

© 2023 by the authors.In the presented study, a novel approach for thermal atomic layer deposition (ALD) of Al2O3 thin films using plasma-activated water (PAW) as a co-reactant, replacing traditionally employed deionized (DI) water, is introduced. Utilizing ex situ PAW achieves up to a 16.4% increase in the growth per cycle (GPC) of Al2O3 films, consistent with results from plasma-enhanced atomic layer deposition (PEALD). Time-resolved mass spectrometry (TRMS) revealed disparities in CH4 partial pressures between TMA reactions with DI water and PAW, with PAW demonstrating enhanced reactivity. Reactive oxygen species (ROS), namely H2O2 and O3, are posited to activate Si(100) substrate sites, thereby improving GPC and film quality. Specifically, Al2O3 films grown with PAW pH = 3.1 displayed optimal stoichiometry, reduced carbon content, and an expanded bandgap. This study thus establishes “PAW-ALD” as a descriptor for this ALD variation and highlights the significance of comprehensive assessments of PAW in ALD processes.

© 2023 Elsevier LtdSurface acoustic wave (SAW) sensors enhanced by a graphenic sensitive layer offer improved electrical response uniformity, and recent research has explored their potential for use in point-of-care platforms. These devices offer a unique combination of cost effectiveness, ease of handling, manufacturability, and remarkable sensor performance. This article summarizes the latest advancements in SAW sensors with graphenic-based nanomaterials, including their fabrication, operation mechanisms, and properties. Several recent studies are reviewed and compared to conventional SAW sensors. Furthermore, the challenges and prospects of using graphenic-based structures to enhance SAW devices and produce rapid actionable results are discussed.

© 2023AlGaN thin films with different Al content were grown via reactive magnetron sputtering onto glass substrates using independent Al and Ga targets. The quality of the films was analyzed using X-ray diffraction, Raman spectroscopy, energy dispersive spectroscopy, and UV-Vis spectrophotometry. The results show that the Al content can be effectively controlled by tuning the power ratio applied to the independent targets in different absolute situations. Moreover, all produced samples presented only wurtzite structure without indication of other phases on both X-ray diffraction and Raman spectroscopy analyses. Overall, the properties of the films had a strong correlation with the composition, such as the expected blue shift of the optical bandgap and the Raman phonon modes, and the lattice cell expansion with increasing Al content. In addition, a higher c-orientation texture together with a sharper diffraction peak were observed for samples with more Al.

© 2023 by the authors.In this study, we report the use of a radiofrequency plasma-assisted chemical vapor deposition (RF-CVD) system with a hollow cathode geometry to hydrogenate anatase TiO2 thin films. The goal was to create black TiO2 films with improved light absorption capabilities. The initial TiO2 was developed through magnetron sputtering, and this study specifically investigated the impact of hollow cathode hydrogen plasma (HCHP) treatment duration on the crucial characteristics of the resulting black TiO2 films. The HCHP treatment effectively created in-bandgap states in the TiO2 structure, leading to enhanced light absorption and improved conductivity. Morphological analysis showed a 24% surface area increase after 15 min of treatment. Wettability and surface energy results displayed nonlinear behavior, highlighting the influence of morphology on hydrophilicity improvement. The anatase TiO2 phase remained consistent, as confirmed by diffractograms. Raman analysis revealed structural alterations and induced lattice defects. Treated samples exhibited outstanding photodegradation performance, removing over 45% of methylene blue dye compared to ~25% by the pristine TiO2 film. The study emphasized the significant impact of 15-min hydrogenation on the HCHP treatment. The research provided valuable insights into the role of hydrogenation time using the HCHP treatment route on anatase TiO2 thin films and demonstrated the potential of the produced black TiO2 thin films for photocatalytic applications.

© 2023 The Author(s)We report a joint experimental and theoretical study of the structural and vibrational properties of C-type bulk Y2O3 under hydrostatic compression. The combination of high-pressure X-ray diffraction and Raman scattering experimental measurements with ab initio theoretical calculations on bulk Y2O3 allows us to confirm the cubic (C-type) – monoclinic (B-type) – trigonal (A-type) phase transition sequence on the upstroke and the trigonal-monoclinic phase transition on the downstroke. This result reconciles with the results already found in related rare-earth sesquioxides of cations with similar ionic radii as Y, such as Ho2O3 and Dy2O3, and ends with the controversy regarding the existence of the intermediate monoclinic phase between the cubic and trigonal phases in pure bulk Y2O3 on the upstroke. As a byproduct, the good agreement between experimental and calculated results allows us to use extensive theoretical data to discuss the structural and vibrational behavior of the three phases of Y2O3 under compression, thus allowing a more detailed understanding of the effect of pressure on rare-earth sesquioxides than previous studies.

© 2023, The Author(s), under exclusive licence to the Korean Fiber Society.This work presents permethrin (15%)-based monomers polymerisation in polyamide fabrics using hybrid corona–dielectric barrier discharge (DBD) to potentiate insect–parasite repellency functionalities in polyamide fabrics. First of all, the electric characterisation of the discharge was made using the Lissajous figure method for determining the plasma dosage (2841 W min m−2). Before the polymerisation process, the polyamide fabric was activated by DBD discharge, operating at 23 kHz and voltage amplitude of 12.5 kV in atmospheric pressure. After that, the polymerisation process is initiated by injecting permethrin into the system, maintaining the operational parameters used in the activation process. The non-activated and activated polyamide fabrics measured the static and dynamic contact angle, showing a variation from 120° (non-activated) to 34° (immediately after plasma activation). The chemical structure of synthesised permethrin was evaluated by Fourier transformed infrared (FTIR) spectroscopy to confirm the polymerisation (deposition) of permethrin on the fabric surface; it is possible to observe the 648 cm−1 bands that are associated with asymmetric vibration of the C–Cl bonds, but most evident change occurs at 1045 cm−1, which is associated with cyclopropyl group vibrations. Field emission scanning electron microscopy (FESEM) analysis was used to evaluate the possible degradation of the fabric surface when exposed to plasma activation and the homogeneity of the permethrin coating in the fibres after the polymerisation. The energy dispersive spectrometer (EDS) was used to confirm the polymerisation and the distribution of the permethrin in the fabric.

© 2023 Universidade Federal de Sao Carlos. All rights reserved.This work reports on the properties of GaN films grown by reactive magnetron sputtering onto glass substrate kept at relatively low temperature (400°C), using different RF power applied to the Ga target. Their structural, morphological, vibrational and optical properties were characterized by X-ray diffraction, atomic force and scanning electron microscopies, Raman spectroscopy and UV-vis spectrophotometry. The films have wurtzite phase with strong preferential orientation in the c-axis direction. Moreover, two clear contributions to the (0002) diffraction peak could be found, indicating the presence of two different morphologies, which were discussed in terms of the formation of an intermediate layer between the substrate and a dominating columnar-like microstructured film.

© 2023 Universidade Federal de Sao Carlos. All rights reserved.In this work, a thermal plasma-based ablation test system was used to evaluate the ablative performance of the EPDM composite. The system produces a high enthalpy plasma jet generated by a plasma (DC) torch, operating at atmospheric pressure using compressed air as working gas, enabling the variation of the thermal flux concerned with the studied EPDM composites. The samples were characterized using Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), Fourier-Transform Infrared spectroscopy (FTIR), and Thermogravimetric Analysis (TGA) to investigate the morphology, mass-loss rate, the reaction layer (char formation), and chemical changes of the samples for each thermal flux. For a complete evaluation, the thermal fluxes were varied in 0.30, 0.45, 0.60, 0.75, and 0.90 MW/m2 and for each thermal flux, disk-shape samples remained exposed to the plasma jet for 10s. During the plasma jet exposure time, the temperatures of the surface and the back of the samples were collected to verify the formed char layer’s insulator capacity and the samples’ thermal diffusivity for each experimental condition. The mass loss is continuous under the thermal fluxes of 0.30 and 0.45 MW/m2, stabilizing at 60% until 0.75 MW/m2. The formed char layer begins to lose its protective capacity, evidenced by the size decrease (from 800 µm to 700 µm), due to the ablation process of the reaction layer from the thermal flux of 0.90 MW/m2

© 2022, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.Thermal plasma-assisted processing is an effective process for the synthesis of gas (CO and H2) and carbonaceous materials production from industrial waste. In this paper, a DC plasma torch designed with two vortices chambers has been developed, and its characteristics have been experimentally tested. The plasma torch operates with different plasma working gases, including steam. The results of coal tar pitch (CTP) processing will be presented as a possible ecological application. CTP is a waste from the steel industry mainly composed of polycyclic aromatic hydrocarbons. The experimental results will be discussed with thermodynamic calculations and numerical simulation of the heat and mass transfer in the DC plasma torch and the chemical reaction chamber. The simulations were carried out to clarify the regions of gas flow and temperatures for producing synthesis gas and carbon nanomaterial. The results enable one to predict the produced gas composition and carbon nanomaterial properties. The physicochemical properties of carbon nanomaterial and synthesis gas show high efficiency in converting CTP into high-value-added products.

© 2022 Society.This is an experimental study on the decolorization efficiency and the degradation of organic compounds from textile wastewater by the ozonation process in a batch system. The effects of different sample volumes of textile wastewater over time were investigated. The experiments were performed in a 1 L glass reactor with a magnetic stirrer and a bubble diffuser at the bottom to feed the ozone. The applied cumulative ozone dosage varied at 120 gO3 L−1, 60 gO3 L−1, and 30 gO3 L−1, and the total interaction time for each test was 1 h. To investigate the physicochemical properties of the textile wastewater (solid and liquid phases) before and after the treatment, multiple analytical characterization methods were used: Thermal Gravimetric Analysis, Scanning Electron Microscopy coupled with Energy-Dispersive X-ray Spectroscopy, X-ray diffraction, Fourier Transform Infrared spectroscopy, and Spectrophotometer. The most perceptive change was observed in the color of the liquid medium, which turned from black to transparent, and a visual color number indicator known as DurchsichtFarbZahl (DFZ) was used for the evaluation of this process. Absorbance values decreased about 3.5 times after 5 min of treatment with a 0.15 L sample volume, and these values differed for tests with larger sample volumes. FTIR spectroscopy demonstrated that the bands’ intensities associated with the C − H, C − N, and C − O decrease during treatment. On the other hand, it was possible to conclude that combining treatment methods to improve the degradation of persistent compounds after the ozonation process is necessary. Finally, the ozonation of the textile wastewater proved to be effective at removing color due to its high reaction capacity.

© 2021 Informa UK Limited, trading as Taylor & Francis Group.The processing of coal tar pitch (CTP) to produce clean fuel gas and carbon black (CB) is studied in a plasma reactor equipped with a direct-current plasma torch. The composition of the gas produced and energy costs were estimated theoretically for the CTP pyrolysis and gasification processes by two oxidants, namely oxygen and water vapor. We have found that the main gaseous compounds obtained in the pyrolysis and gasification processes are hydrogen (H2), carbon monoxide (CO), and very often carbon dioxide (CO2). For the pyrolysis case, the mean value of the synthesis gas concentration reaches a major value of 98 vol.% (H2–81 vol.%, CO–17. vol.%). However, only 23% of the initial CTP is transformed into gas phase at 1100 K and its content increases up to 37.4% at a temperature of 3000 K. For oxygen gasification, the syngas quantity is little less compared to the pyrolysis case and attains 96.6 vol.% (H2–26.5 vol.%, CO–70.1 vol.%) for T > 1100 K. An intermediate syngas content for the water steam gasification is 97.8 vol.% (with H2–55.8 vol.% and CO–42.0 vol.%). The CB produced was composed of well-defined spherical particles of 30-nm size. Furthermore, it is composed of carbon (98.2%), and followed by oxygen (1.8%) with a surface area of 97 m2 g−1. The thermal plasma system shows high efficiency in conversion of CTP into high-value-added products.

© 2022 Elsevier LtdThe corrosion behaviour of laser and plasma nitrided β-Ti12Mo6Zr2Fe biomaterial was evaluated. Polarisation curves and electrochemical impedance spectroscopy were performed in simulated body fluid (SBF) at 37 °C. Both treatments formed titanium-nitride at the alloy's surface, and significantly improved the corrosion performance of the alloy. At anodic potentials of the order of 1.0 V, the titanium-nitride layer seems to oxidise, independent of the nitriding process. Nanometric fissures formed on the plasma titanium-nitride layer seems to govern the impedance response at low frequencies, exposing the substrate to the electrolyte. Laser titanium-nitride layer is thicker and lead to a better corrosion performance.

© 2022 Elsevier B.V.Patients with skin diseases may have their quality of life affected. Many of them have chronic skin lesions or some form of complication during the healing process. Ozone therapy is a low-cost method with efficient results, including the easy application of ozonized oil to the skin. However, studies report divergent times for the ozonation process of vegetable oil. This work aims to characterize, using the Fourier transform infrared (FT-IR) spectroscopy technique, sunflower oil ozonized at different exposure times. Nine samples of oil were treated up to 90 min with ozone (maximum applied ozone dosage of 117.0 g L−1) and, together with the control sample, were analyzed by FT-IR and the spectra deconvoluted in relation to the main bands observed by the second derivative. Two spectral regions were investigated: 1800 – 800 cm−1 and 3050 – 2800 cm−1. The results indicated a statistically significant difference between the spectra, especially after 20 min of the ozonation process. A decrease in oil temperature was observed 30 min after the beginning of the ozonation process, with a decrease in the intensity of the –CH stretching band of the fragment –C[dbnd]C–H above 3000 cm−1, an increase of the intensity of the C–H stretching bands of the CH3 groups, decrease of intensity of the stretching bands of –C[dbnd]C– chemical bond, and constant intensity of the –C[dbnd]O stretching band.

© 2022 by the authors.The growing need for increasingly miniaturized devices has placed high importance and demands on nanofabrication technologies with high-quality, low temperatures, and low-cost techniques. In the past few years, the development and recent advances in atomic layer deposition (ALD) processes boosted interest in their use in advanced electronic and nano/microelectromechanical systems (NEMS/MEMS) device manufacturing. In this context, non-thermal plasma (NTP) technology has been highlighted because it allowed the ALD technique to expand its process window and the fabrication of several nanomaterials at reduced temperatures, allowing thermosensitive substrates to be covered with good formability and uniformity. In this review article, we comprehensively describe how the NTP changed the ALD universe and expanded it in device fabrication for different applications. We also present an overview of the efforts and developed strategies to gather the NTP and ALD technologies with the consecutive formation of plasma-assisted ALD (PA-ALD) technique, which has been successfully applied in nanofabrication and surface modification. The advantages and limitations currently faced by this technique are presented and discussed. We conclude this review by showing the atomic layer etching (ALE) technique, another development of NTP and ALD junction that has gained more and more attention by allowing significant advancements in plasma-assisted nanofabrication.

© 2022 by the authors.This work reports on the (zero-dimensional) global model study of argon plasma chemistry for a cylindrical thruster based on inductively coupled plasma (ICP) whose output has a system of two grids polarized with each other with direct current potential. The global model developed is based on particle and energy balance equations, where the latter considers both charged and neutral species. Thus, the model allows the determination of the neutral gas temperature. Finally, this study also investigated the role of excited species in plasma chemistry especially in the ions production and its implications for propulsion parameters, such as thrust. For this, the study was carried out in two different scenarios: (1) one taking into account the metastable species Arr and Arp (multi-step ionization), and (2) the other without these species (single-step ionization). Results indicates a distinct behavior of electron temperature with radiofrequency (RF) power for the investigated cases. On the other hand, the gas temperature is almost the same for investigated power range of up to 900 W. Concern propulsion analysis, a thrust of 40 mN at 450 W was verified for case (1), which represents a remarkable thrust value for electric thrusters.

© 2022 Elsevier LtdThe management of radioactive waste is a worldwide activity based on the guidelines of the International Atomic Energy Agency (IAEA), and all stages of management require scientifically proven methods for possible deployment. The management of radioactive waste is a huge challenge due to the high risk in the collection, gathering, transport, handling, and storage. In this study, a thermal plasma treatment process was evaluated for its efficiency to process solid radioactive waste. Experiments were carried out with the application of stable isotopes of Lead, Iodine, Cobalt, and Cesium. After the thermal plasma treatments, the slag and the residual gas were analyzed to verify the influence of process time and discharge power on the efficiency of the process. The treatment for 25 min and 10 kW was sufficient to reduce the mass by 50% of the slag. When the applied power was increased to 15 kW, an expressive reduction in the treatment time (10 min) was able to promote the same mass reduction. The results indicated that the treatment of radioactive waste by thermal plasma is a promising method to manage and reduce the mass and volume for the final disposal.

© 2023 Elsevier Inc. All rights reserved.Solar cells and photovoltaic devices are based overall on metal oxides and heterostructures. This is a technology in advance, with remarkable interest due to its low impact on the environment in comparison to the most used forms of energy conversion. Additionally, the oxides are most abundant, easy, and less expensive to obtain compared to other materials for such applications. Although the metal oxide–based photovoltaic devices show, usually, low conversion efficiency, some studies have shown capable of obtaining PCE higher than 10% or 20% using enhanced heterostructures. This chapter presented a review of the state of the art of metal oxide heterostructures applied mainly in photovoltaic devices and solar cells. A special focus is given to studies related to some of the most applied materials, such as ZnO, ZnO:Al, (AZO), and TiO2, and to heterostructures based on metallic oxides of copper, zinc, magnesium, vanadium, etc.

© 2022 The Author(s).Background. New surface treatments have been proposed to expand the clinical indications of zirconia prostheses. This study aimed to evaluate the effect of silica and fluorine nanofilms on zirconia ceramic on the resin cement bond strength. Methods. Zirconia blocks and discs underwent different surface treatments: untreated zirconia (CON), sandblasted, silica-coated alumina particles (30 µm) (SC), silica nanofilm (SN), and fluorine nanofilm (FN). Nanofilm deposition was performed through plasma enhanced chemical vapor deposition (PECVD). Zirconia surfaces were characterized on disks by morphology (atomic force microscopy, AFM), chemical analysis (x-ray photoelectron spectroscopy, XPS), and contact angle analysis. A silane coupling agent was applied on each treated surface, and a cylinder of resin cement was built up. Half of the specimens in each group were submitted to 6000 thermal cycles (TC). Bond strength was analyzed using the shear test, and the fractographic analysis was performed with stereomicroscopy and SEM/EDS. Statistical analysis was performed through one-way ANOVA and Tukey test in the non-aged and aged specimens. Results. Nanofilms modified the zirconia surface, which became more hydrophilic and chemically reactive. Chemical bonding between Si-O was found in SN, and FN promoted a fluorination process on the ceramic surface, converting zirconia into zirconium oxyfluoride. Specimens of the SN (TC) group failed on pre-testing. FN (TC) bond strength (3.8 MPa) was lower than SC (TC) and CON (TC) after shearing. Adhesive failure predominated in the experimental groups. Silica nanofilm failure occurred after aging. Conclusion. Silica and fluorine nanofilms deposited by PECVD did not promote effective bonding between zirconia and resin cement.

© 2022 Universidade Federal de Sao Carlos. All rights reserved.This work reports the properties of GaN films grown onto c-Si (100) at relatively low substrate temperature (400°C) by reactive magnetron sputtering. The study depicts the effect of working pressure and RF power on the GaN film structural, vibrational and optical properties characterized by X-ray diffraction, atomic force and scanning electron microscopies, Raman spectroscopy and spectroscopic ellipsometry. Unusual low pressure deposition condition (0.40 Pa) was achieved by using a separated argon inlet directed to the Ga target surface, resulting in improved crystalline quality of the films. In this condition, the preferential crystalline orientation, the surface morphology and the optical gap of the GaN films show a strong dependence on the RF power applied to the Ga target, where low RF power (30-60 W) was responsible for increasing the c-axis orientation and the optical gap, while higher RF power (75-90 W) decreased the overall crystal quality and increased the surface roughness.

© 2025 The AuthorsThe present work performs a review for using hydrogen in aircraft propulsion systems analyzing challenges and opportunities with the two main driveline architectures: direct combustion of hydrogen and fuel cells. First, the capability of hydrogen aircraft to become more energy efficient than conventional aircraft are discussed on system level, by extending previous review work. Then, challenges for hydrogen combustion and ways to limit emissions by lean direct injection and micromix combustion are discussed. Polymer electrolyte membrane (PEM) and solid oxide fuel cells are reviewed and the outlook for high temperature PEM fuel cells and challenges with per- and polyfluoroalkyl substances (PFAS) emissions are discussed. Dual fuel aircraft and flexible combustion are discussed as ways to provide a transition to a hydrogen economy. Additionally, hybrid configurations and new cycles that simplify hydrogen integration are reviewed. Finally, recent promising results on water emissions and contrail formation for hydrogen combusting aircraft are discussed.

© 2025 by the authors.Adverse pressure gradients are intrinsic to compressor flow behavior and are further intensified by secondary effects associated with rotor tip clearance flow interactions. Tip clearance generates leakage flow, which leads to the formation of tip leakage vortices, a major contributor to aerodynamic losses in axial compressors. These vortices significantly influence both compressor performance and operational stability. Extensive prior research has demonstrated that passive casing treatments, particularly axial slots, can substantially improve the stall margin in axial compressors. In this work, the performance of a new casing treatment geometry is investigated using the concept of recirculating flow within semi-circular axial slots. The proposed casing treatment geometry builds upon recent experimental findings involving single-rotor configurations. It was applied to the first rotor row of a three-and-a-half-stage (3.5-stage) axial compressor comprising an inlet guide vane followed by three rotor–stator stages. The numerical model incorporates axial slots with a novel periodic interface approach implemented in a multistage compressor simulation. Three-dimensional steady-state RANS (Reynolds Average Navier-Stokes) simulations were performed to investigate the aerodynamic effects of the casing treatment across various rotational speeds. The results for the casing treatment configuration were compared with those of a baseline smooth casing. The introduction of the new casing treatment produced noticeable modifications to the internal flow structure, particularly in the tip region, resulting in improved overall compressor stability within the operating range of 85 to 100% of design speed.

© 2025 by the authors.Turbines are rotating machines that generate power by the expansion of a fluid; due to their characteristics, these turbomachines are widely applied in aerospace propulsion systems. Due to the clearance between the rotor blade tip and casing, there is a leakage flow from the blade pressure to the suction sides, which generates energy loss. There are different strategies that can be applied to avoid part of this loss; one of them is the application of so-called desensitization techniques. The application of these techniques on gas turbines has been widely evaluated; however, there is a lack of analyses of hydraulic turbines. This study is a continuation of earlier analyses conducted during the first stage of the hydraulic axial turbine used in the low-pressure oxidizer turbopump (LPOTP) of the space shuttle main engine (SSME). The previous work analyzed the application of squealer geometries at the rotor tip. In the present paper, winglet geometry techniques are investigated based on three-dimensional flowfield calculations. The commercial CFX v.19.2 and ICEM v.19.2 software were used, respectively, on the numerical simulations and computational mesh generation. Experimental results published by the National Aeronautics and Space Administration (NASA) and data from previous works were used on the computational model validation. The parametric analysis was conducted by varying the thickness and width of the winglet. The results obtained show that by increasing the winglet thickness, the stage efficiency is also increased. However, the geometric dimension of its width has minimal impact on this result. An average efficiency increase of 2.0% was observed across the entire turbine operational range. In the case of the squealer, for the design point, the maximum efficiency improvement was 1.62%, compared to the current improvement of 2.23% using the winglet desensitization technique. It was found that the proposed geometries application also changes the cavitation occurrence along the stage, which is a relevant result, since it can impact the turbine life cycle.

Copyright © 2025 by ASME.Due to the growing relevance of mitigating climate change, and the race to improve the energy efficiency of aircrafts, aiming a goal of net-zero emissions of CO2 by 2050, the aircraft propellers have been receiving more attention, as they could represent the next innovation towards the efficiency improvements, especially due to the possibility of hybrid/electrical propulsion. In this context, this article consists of a critical overview of propeller design methods, depicting some relevant classical methods of designing propellers, such as the Blade Element Momentum Theory by Glauert, Vortex Theories, developed by Betz, Goldstein, and Theodorsen, as well as methods to design propellers that are intended to increase the lift on the wings. The straightforward Propeller Design procedures by Larrabee, Adkins Liebeck, and Wald, which are based on these theories, are also covered and compared. In addition, this paper also covers the final design and optimization, showing how computational methods, such as VLM and CFD, are being used in the literature to improve preliminary designs and model the interaction between the propellers and the wing/body. The objective of this paper is to provide a comprehensive reference for researchers and students, summarizing the state-of-Art of propeller design and optimization, for those who intend to work with propellers for green aviation.

© 2024The aviation industry accounts for part of the CO2 emissions contributing to climate change. The industry has established a target to reduce 2050 net aviation carbon emissions by 50 % relative to 2005 levels. With this in mind, waste heat recovery is a key pathway to achieve reduced emissions and improve system efficiency. The waste heat may potentially be converted to electric power using a supercritical CO2 Brayton power cycle. The sCO2 power system offers the advantage of compactness owing to the high working fluid density, which is an important consideration for aircraft performance. The present work focuses on the integration of the sCO2 power system into the aircraft propulsion system and evaluation of its performance. Detailed optimization of the sCO2 waste heat system will be evaluated with a focus on cycle efficiency and net power under different operating conditions, including ground, takeoff, climb, cruise, and landing operations. The study is divided into two parts with two different turbofan engines, one with a nominal thrust of 30 kN and the other with a nominal thrust of 9 kN. The first part shows the effect and operation of the waste heat recovery unit under the different operating conditions. The second part is focused on cycle optimization and performance evaluation. The results demonstrate the potential of waste heat recovery during a range of operational conditions. The sCO2 cycle efficiency can reach between 25 and 39 % (depending on aircraft engine) with net power output in the range of 100 to 260 kW.

© 2024 Elsevier LtdThe global increase in food demand drives the need for efficient and sustainable agricultural practices, particularly in the energy-intensive process of grain drying, which is crucial for maintaining product quality. This study proposes the exergetic and environmental analysis of a hybrid electric column dryer for soybeans, comparing its performance across four distinct national contexts: Paraguay, Brazil, the United States, and China. The aim is to explore how different energy matrices and degrees of hybridization influence the energy and environmental costs associated with soybean drying. In addition to considering different energy matrices, the present study advances beyond previous research by coupling the mathematical drying model with thermodynamic analysis. By integrating these aspects, it is possible to conduct thorough simulations and gain insights into the exergetic, environmental, and economic impacts of the drying process. For this, a computational model was developed capable of simulating the drying process of soybeans and determining the conditions of grains and air at the exit of the drying chamber and, thus, performing the First and Second Law analyses with different degrees of hybridization for four countries with different electricity mixes. Results reveal that for thin-layer soybean drying dynamics at T = 80 °C and v = 0.5 m/s, approximately 68.2 min were needed to reduce grain moisture content from 18% w.b (0.22 d.b) to 14% (0.163 d.b), with outlet temperatures of θ = 67.57 °C for grains and T = 71.7 °C for air. The final water content of the drying air was 0.021 kgw/kga. Exergetic cost analysis revealed significant variations among countries, with Paraguay exhibiting the greatest difference between completely fossil and purely electrical cases (433.5 kJ/kgg). Environmental cost analysis showed substantial differences in electrical energy use for drying, particularly in countries with predominantly renewable energy matrices. Paraguay showed the highest emissions variation with a purely electrical system, differing by 27.55 gCO2/kgg compared to the pure fossil case. Brazil, the United States, and China had differences of 25.33, 17.4, and 11.90 gCO2/kgg, respectively. From an economic standpoint, hybridization was found to be unfeasible in Brazil due to high electricity prices, while theoretically favorable in China, Paraguay, and the United States. Paraguay had the lowest drying cost at 2.63 US$/tong, followed by China, the United States, and Brazil with 3.92, 4.74, and 15.79 US$/tong, respectively. These analyses underscore the importance of comprehensive studies in evaluating process hybridization. Considering electricity mix composition and reliable life cycle analysis data is crucial for obtaining meaningful results. Integrated exergetic, environmental, and economic analyses are essential for guiding energy use decision-making processes.

© 2024 by the authors.The internal losses in the tip clearance region strongly influence the compressor performance and its operational range. Previous research proved that passive wall treatments with circumferential grooves in axial compressors effectively increase the compressor stall margin. The vortex generated inside the circumferential grooves creates a resistance to the flow that leaks into the tip clearance region of the compressor. However, most works found in the literature on circumferential grooves in axial compressors deal only with high-performance single-stage axial compressors. Therefore, there is a need to investigate and analyze the behavior of circumferential grooves in a multi-stage environment. In the present work, a passive wall treatment with circumferential grooves was implemented in a multi-stage axial compressor. Different configurations of circumferential grooves were created at the casing of the first and second rotor rows used in a four-stage axial flow compressor. Numerical simulations were performed to evaluate the influence of the circumferential grooves on the performance of a multi-stage axial compressor. The results obtained after the simulations for the different circumferential groove configurations were compared with the results obtained for the compressor without casing treatment (smooth wall) for different rotational speeds. Furthermore, the complete compressor map characteristics were simulated for the different casing treatment configurations, and the results were compared with the compressor characteristics of the smooth wall case. The passive wall treatment with circumferential grooves produced changes in the multi-stage axial compressor flow field, especially in the tip clearance region, improving the compressor stability mainly for part load speeds.

© 2024 Tiago Andrei Adamczevski, Luiz Vitor Tozi, João Guilherme Vidal do Nascimento, Cleverson Bringhenti, Jesuíno Takachi Tomita.This paper presents the development of a gas turbine simulator based on an application of a real turbogenerator used to generate electricity on an offshore oil platform, the configuration is a turboshaft with free power turbine. The compressor, turbines and the control system were developed using specific methodologies. The development of the simulator was done using the Simulink environment in Matlab®. The development was done using blocks to represent each one of the main components in the engine. A stage stacking methodology based on the real geometry for each stage was adopted to create the compressor maps. The map was used in lookup tables blocks with help of auxiliary coordinates, also known as beta lines. To model both turbines were applied an ellipse equation also known as Stodola’s law. The engine simulator model was tested in an open loop and the results evaluated with the manual data from the engine.

© 2024 by the authors.The ratio between blade height and chord, named the aspect ratio (AR), plays an important role in compressor aerodynamic design. Once selected, it influences stage performance, blade losses and the stage stability margin. The choice of the design AR involves both aerodynamic and mechanical considerations, and an aim is frequently to achieve the desired operating range while maximizing efficiency. For a fixed set of aerodynamic and geometric parameters, there will be an optimal choice of AR that achieves a maximum efficiency. However, for a state-of-the-art aero-engine design, optimality means multi-objective optimality, that is, reaching the highest possible efficiency for a number of operating points while achieving a sufficient stability margin. To this end, the influence of the AR on the performance of the first rotor row of a multistage, multi-objective, high-speed compressor design is analyzed. A careful setup of the high-speed aerodynamic design problem allows the effect of the AR to be isolated. Close to the optimal AR, only a modest efficiency variation is observed, but a considerable change in compressor stability margin (SM) is noted. Decreasing the AR allows for increasing efficiency, but at the expense of a reduced surge margin. This allows the designer to trade efficiency for stability. Increasing the AR, however, is shown to reduce both the surge margin and efficiency; hence, a distinct optimality in stability is observed for the analyzed rotor blade row. In this work, optimality in the surge margin with respect to the AR is observed, whereas there is a close to optimal efficiency. The predicted range from AR = 1.10 to AR = 1.64 is only indicative, considering that the definition of multi-objective optimality requires balancing efficiency and the surge margin and that the choice of balancing these two criteria requires making a design choice along a pareto optimal front.

© 2024 by ASME.This work aims to provide a methodology for defining the design point for industrial gas turbine considering the economic, environmental, and engine performance aspects. The definition of the design point is a key step in the development project of a gas turbine since this definition involves the analysis of several operational points to verify if the desired performance can be obtained. Thus, to extend the methodology presented in the literature developed for micro-turbines to consider industrial gas turbines a computer program was developed in MATLAB®. This program is capable of performing thermodynamic calculations for design point definition and of performing single- and multi-objective thermoeconomic and thermodynamic optimizations using genetic algorithms. For the optimization process, total cost minimization, yield maximization, and gas turbine-specific work maximization were chosen as objective functions. The decision variables chosen were compressor pressure ratio, compressor polytropic efficiency, turbine polytropic efficiency, and maximum cycle temperature. For the calculation of economic aspects, fixed costs (equipment, installations, land acquisition cost, etc.) and variable costs (fuel, emissions, and operation and maintenance costs) were considered. The emission cost of NOx, CO, and UHC was considered for the environmental cost calculations. The thermodynamic calculations were based on enthalpy and entropy. The developed computer program was validated by simulating a commercial gas turbine and comparing the results obtained, also using a commercial program, GASTURB®. The presented optimization process shows results for a single objective, two objectives, and three objectives, where the results show a comparison between different design points obtained. The software developed will be of great assistance in the learning of engineering students.

© 2024 by ASME.The air conditioning system of executive, commercial, or military aircraft heavily relies on air cycle machines due to the availability of engine bleed air and their lightness and reliability compared to vapor cycle systems. The type of application, weight, refrigeration capacity, financial aspects, size, performance, and other specific design requirements drive the selection of suitable equipment for a particular aircraft. The motivation of this paper has been based on summarize the main concepts of the aeronautical environmental control system, as well as the mathematical aspects underlying the modeling of a simple/bootstrap air cycle unit in a software. The main aim is to develop software that can generate high level requirements that would be refined during the development phase of an aeronautical air conditioning system. It will be greatly benefit for engineers and students in the design of aeronautical air conditioning systems to better understand and to meet the design requirements. The results demonstrate the influence of the water-sprayer and chilled-recirculation system on air cycle performance and cabin inlet temperature, respectively. They also show changes in certain parameters of interest such as a function of altitude, power consumed by the secondary compressor, and air cycle machine fan. The computational model has proven to be a useful tool for performing parametric studies and evaluating critical points in designing and selecting an air conditioning unit based on a simple/bootstrap air cycle with humid air (any quantity of moist) as the working fluid.

© 2024 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.Decarbonization of the aviation sector is a key factor for current and future systems. Waste Heat Recovery (WHR) may be used to convert waste energy to electric power by using a bottoming cycle, which can reduce the overall fuel requirement of the airplane. One of the potential bottoming cycles for aircraft application is a Supercritical CO2 (sCO2) power system. The sCO2 power system has advantages because of the component compactness, which is crucial for aircraft integration. However, the main challenge for aircraft integration is the size and weight of the heat exchangers. The present work focuses on the performance of the Supercritical CO2 power system in both current and next-generation aircraft engines considering an innovative and advanced design of the sCO2 heat exchangers (cooler and primary heat exchanger). The first part of the work is focused on the analysis of the sCO2 WHR system for an aircraft engine. The second part of the work is focused on a detailed heat exchanger selection, design and optimization based on the aircraft engine parameters. The results show the potential of WHR utilization, which may generate an additional 100 - 200 kW. However, the heat exchangers may increase overall weight of the aircraft. For this reason, an advanced design is necessary.

© 2023, The Author(s), under exclusive licence to The Brazilian Society of Mechanical Sciences and Engineering.The Turbofan engine represents the type of propulsive technology mostly used in commercial aircrafts, and until that the new disruptive technologies take place, researches to optimize this propulsive system shall be continued to reduce the environmental impacts. The aim of this paper is to propose a methodology for the low-pressure system preliminary design (fan/low-pressure turbine), based on aircraft cruise thrust adjustment from commercial off-the-shelf turbofan engine, focusing on reducing specific fuel consumption for the individual aircraft mission. This work is carried out according to the following steps: (i) model development with calculation methodology for velocity diagram flow angles applied to the low-pressure system; (ii) estimation of baseline low-pressure system design parameters from limited engine data (an integrated engine aircraft model developed in the Gasturb and MATLAB commercial softwares are applied); (iii) evaluation of the strategies to increase the low-pressure system component efficiencies and their implementation by computer simulation; (iv) reapplication of the calculation methodology for estimation of the velocity diagram flow angles considering the adjusted low-pressure system components; and (v) analysis of the adjustment proposal results considering the matching between the lowest specific fuel consumption and the net thrust required for the cruise flight phase of the aircraft. As a final result, it demonstrates that the proposed strategies are promising for the adjustment of the low-pressure system in the preliminary design scope, and this approach may be considered feasibility from the standpoint of the engine manufacturer implementation, since the engine core and its external sizing do not affected.

© 2023 by ASME.Evaporative cooling systems are commonly used in thermoelectric plants to cool the air at gas turbines inlet, improving the performance of these engines. Normally, the evaporative cooling is modeled as adiabatic saturation and, in this case, the water-air equilibrium temperature depends only on the atmospheric air properties. However, other factors such as the water temperature that supplies the equipment and the ratio between the mass flow rates of water and air, also affect the equilibrium conditions of these systems. This work presents three methodologies to calculate the air temperature in equilibrium state, considering all the factors mentioned. The methodologies were implemented in a computer program written in FORTRAN. In all cases tested, the results obtained by the three models showed high convergence. As an example, for 70 different sets of inputs, the absolute and relative differences of the results were below 0.3236°C and 1.2480%, respectively. A statistical study, also on this sample of results, revealed that, for a confidence level of 99%, the hypothesis of the equivalence between the methods cannot be rejected.

© 2023, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.Correction Notice Reference 5 should be: L. Vesely, J. S. Kapat, C. Bringhenti, J. T. Tomita, M. F. Stoia, and K. Jui, “sCO2 Waste Heat Recovery System for Aircraft Engines,” AIAA 2022-1407. AIAA SCITECH 2022 Forum. January 2022. doi: https://doi.org/10.2514/6.2022-1407.

© 2023, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.The present work investigates the effect of reordering the nodes and elements of a grid according to the Hilbert curves on the cache utilization in an in-house parallel CFD code. A sorting algorithm is proposed based on domain decomposition techniques and the execution times are compared to those obtained by the structured grid format.

© 2023, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.Waste Heat Recovery is one of the key pathways to achieving reduced emissions and improving system efficiency. The Waste Heat Recovery (WHR) may be used to convert the waste energy to electric power by using a bottoming cycle. One of the potential bottoming cycles for aircraft application is a Supercritical CO2 (sCO2) power system. The sCO2 power system has advantages because of the component compactness, which is a key factor for aircraft integration. The present work focuses on the performance of the Supercritical CO2 power system in both the current and the next-generation aircraft engines considering the techno-economic evaluation of the bottoming cycle. The techno-economic evaluation needs to consider bottoming cycle integration and potential fuels, such as hydrogen, ammonia, or sustainable aviation fuel (SAF). The first part of the work is focused on the analysis of the sCO2 WHR system for an aircraft engine. The second part of the work is focused on a detailed techno-economic evaluation, including the capital, operation, and maintenance costs. The simulation was done using in-house computer programs for gas turbine performance and the sCO2 cycle. The results show the potential utilization of WHR in different operational regimes: idling on the ground, cruise, landing, and takeoff. The results show that the Waste Heat Recovery unit may generate an additional 100 - 200 kW. However, the additional power will require an additional cost for the system, approximately $ 2 Million.

Copyright © 2023 by ASME.The industry and the academy are continuously developing new approaches, technologies, and models for gas turbine design. However, there was not enough time to cover all the relevant subjects for undergraduate or graduate students in one or two-semester courses. So, in previous works, the authors described a developed interactive platform for the preliminary design of multistage axial flow turbines for uncooled blades and improved it based on the student’s feedback, so it could be as didactic as possible. Its application in the courses offered by the Turbomachines Department at Aeronautics Institute of Technology (ITA) successfully accelerated the learning process of the basics. In the graduate courses, the use of the program granted time to more complex topics, e.g., blade cooling, off-design performance, CFD simulations, manufacture, and machine learning applied to turbomachine design, which were not covered in previous years. The program initiates with the data from thermodynamic cycle calculation and the definition of the main design parameters. Then, it computes the aerothermodynamic properties of the flow stage-by-stage, from hub to tip, and the geometry of the blades. Finally, it estimates the losses by source, iteratively, through the models of Ainley and Mathieson [1], Dunham and Came [2], or Kacker and Okapuu [3]. This work presents some studies performed by the students using the platform. Firstly, it was varied some design key parameters such as loading and flow coefficients, the aspect ratio and the pitch-to-chord ratio of the blades, the airfoil section geometry, and the tip clearance, once at a time while maintaining the others. Then, it was possible to observe how these modifications affected the number of stages required, the stress levels, the machine size, and the isentropic efficiency, tracking the primary sources of loss. After, the students implemented other loss models, such as the one by Craig and Cox [4], aiming to analyze the effect of surface roughness on the losses. Finally, they compared the platform results with CFD simulations and experimental data from turbines developed at the Department. The paper concludes with the students’ insights through the project and comments on how the employed methodology improved their learning process.

Copyright © 2023 by ASME.The inducer is an axial pump that is part of the propellant injection system of Liquid Propellant Rocket Engines (LPRE). It is located at the inlet of the turbopump assembly and is critical for designing high performance LPREs. Its geometric and operational characteristics allow it to operate at low inlet pressures, delaying the appearance of cavitation and allowing the propellant tanks to operate at lower pressures. This allows the tanks to be lighter due to a reduced wall thickness requirement. The inducer also needs to operate harmoniously with the other components of the turbopump, especially with the main impeller which is located just downstream in the system. Therefore, it is important that the flow conditions at the inducer inlet and outlet are known and integrated with the turbopump and tank design. The present work aims to develop a methodology for inducer design based on literature established methods in order to obtain geometry and evaluate the flow conditions in liquid-propelled rocket engine inducer pumps. This work will assess outlet flow and pressure conditions in a way that it is possible to match them with the main impeller inlet. Performance criteria are evaluated in terms of the outlet pressure coefficient, flow coefficient and efficiency focusing exclusively on non-cavitating conditions. Two established analytical methods were implemented, one to provide inducer geometry in terms of system operational requirements and another, from National Aeronautics and Space Administration (NASA), for performance prediction based on geometrical and operational parameters. Further analysis is complemented by simulating the generated geometry in a CFD software. The methods were validated using published experimental data and the performances of the analytical, numerical and experimental results were compared. Results showed that the 3D turbulent CFD simulations provided very good agreement of efficiency. Satisfactory results were obtained for the general trends of characteristic curves over a range of flow rates and the spanwise distribution of key performance parameters near design point. The pressure coefficient was significantly overestimated. The results of the analytical models showed good agreement with simulated CFD results, indicating appropriate calibration of loss coefficients.

Copyright © 2023 by ASME.The use of inducers in turbopumps for liquid propellant rocket engines allowed operation at high rotational speeds, contributing to global vehicle performance improvement. Methods for designing inducers have been explored using analytical methods, experimental data and numerical solutions. The use of CFD for simulating and designing rocket turbopump inducers is a relevant practice because it can rapidly explore scenarios untested in the experimental endeavors for determining empirical functions. This technique also captures more problem details than reduced order analytical solutions. Turbomachines have a different accuracy in terms of solution prediction for different turbulence models and application. The flow specificity of the turbomachinery changes the adequate turbulence model to obtain a more accurate solution. For this reason, it is of interest to investigate how different turbulence modeling predicts the fluid flow behavior and their accuracy to calculate the inducers' performance. The present work aims to investigate the capability of different turbulence models on the performance and flowfield obtained via CFD simulations of an inducer pump. The CFD simulations were performed using a commercial software for k-ε, RNG k-ε and Shear Stress Transport turbulence models. The simulations were performed on a known inducer geometry for which published experimental performance data as a function of operational conditions is available in literature. The present paper discusses the differences in the performance prediction and the flow field calculated for the turbulence models simulated. For the cases studied, the k-ε standard model shows better predictions for the efficiency and head coefficient compared with the experimental data demonstrating their accuracy in solving rotational flows.

Copyright © 2023 by ASME.The boundary layer ingestion (BLI) concept has emerged as a novel technology for reducing aircraft fuel consumption. Several studies designed BLI-fans for aircraft. BLI-propellers, although, have still received little attention, and the choice of open-rotors or ducted propellers is still an open question regarding the best performance. The blade design is also challenging because the BLI-propulsors ingest a nonuniform flow. These aspects emphasize further investigation of unducted and ducted BLI-propulsors and the use of optimization frameworks, coupled with computational fluid dynamics simulations, to design the propeller to adapt to the incoming flow. This paper uses a multi-objective NSGA-II optimization framework, coupled with three-dimensional RANS simulations and radial basis function (RBF) metamodeling, used for the design and optimization of three propeller configurations at cruise conditions: (a) conventional propeller operating in the freestream, (b) unducted BLI-propeller, and (c) ducted BLI-propeller, both ingesting the airframe boundary layer. The optimization results showed a significant increase in chord and a decrease in the blade angles in the BLI configurations, emphasizing that these geometric parameters optimization highly affects the BLI-blade design. The unducted BLI-propeller needs approximately 40% less shaft power than the conventional propeller to generate the same amount of propeller force. The ducted BLI-propeller needs even less power, 47%. The duct contributes to the tip vortex weakening, recovering the swirl, and turning into propeller force, as noticed from 80% of the blade span to the tip. However, the unducted and ducted BLI-configurations presented a higher backward force, 26% and 46%, respectively, compared to the conventional propeller, which can be detrimental and narrow the use of these configurations.

© 2022, The Author(s), under exclusive licence to The Brazilian Society of Mechanical Sciences and Engineering.The costs involved in the design, manufacture, certification and maintenance of a helicopter have grown over the past few years. In the certification phase of embedded systems, their safety levels and their performance requirements are verified. The helicopter engine is a system that must be reliable and capable of providing the necessary power to produce lift and controllability for the aircraft. In this work was developed a computer model to evaluate the helicopter engine’s performance under any flight conditions and the pilot’s inputs. The developed software was incorporated as a module in a flight test simulator at the Flight Tests and Research Institute (IPEV) which belongs to the Brazilian Air Force. This simulation tool allows foreseeing and investigating possible situations that may occur during actual flight tests, improving safety and reducing costs. Using MATLAB® Simulink, it was possible to run at the same time: an iterative and a non-iterative methodology, a control system to set the fuel flow schedule, based on several inputs generated from the thermodynamic model. Based on classic thermodynamics laws and differential equations, the particularities due to the helicopter application were adjusted: the influence of the pilot’s commands; performance requirements; running line control; and the fuel flow control system. The simulation results were compared with commercial gas turbine performance simulation software and with the data provided by the IPEV in five real flight tests. These data were also used for obtaining engine output power requirements according to collective stick position.

© 2022, The Author(s), under exclusive licence to The Brazilian Society of Mechanical Sciences and Engineering.The tip clearance is the gap between the rotor blade row and its casing. In this region, a leakage flow on the rotor blade tip is induced by pressure differences from rotor blade pressure side to suction side, resulting in a loss in the turbomachine efficiency and drop in performance. High pressure turbines (HPT) operate in the limit of the energy transfer process with low-aspect ratio blades and high-pressure loading. The tip clearance loss is significant when compared with other loss sources. To minimize the performance drop, different desensitization techniques were tested for turbulent flow in steady state. First, the HPT developed by NASA in the Energy Efficient Engine (E3) program was studied with its original configuration of rotor tip, also called flat-tip. Then, the winglet was implemented on rotor tip geometry, for both suction and pressure sides. Numerical simulations using the computational fluid dynamics were performed, and the results are compared with experimental data for both cases. The results show that in general, for the same HPT pressure ratio, the use of winglet on the rotor tip pressure side achieved the best results showing an increase in efficiency of 1.025 % for 3.7 of pressure ratio. Even the winglet on the rotor tip suction side presented an efficiency increase of 0.625 % for 3.7 of pressure ratio compared with flat-tip rotor configuration. Overall, both winglet configurations obtained results better than the common rotor blade flat-tip geometry, for the same pressure ratio operational condition.

© 2022, The Author(s), under exclusive licence to The Brazilian Society of Mechanical Sciences and Engineering.For a long time, thermal power plants play important roles in world electricity and are expected to continue, at least, in the next decades. However, the finitude of fossil fuel sources leads to the crucial need for improving the existing power generation systems. In this study, an in-house computational code was developed and validated to evaluate the energy, exergy and economic performance for thermal power plants applications. Based on operating data of an actual lignite coal-fired steam power plant, two cycles were designed and compared. In the cycle in which more components were added, the fuel consumption was 9.44% lower to produce the same amount of power, making more effective use of the fuel resource. This substantial reduction in fuel consumption reflected lower electricity average costs for this plant. Comparing to the electricity price of a country using the same type of fuel, it was found that it could be lower by 1.62 percentage points for household consumers. Although the higher costs with capital investment and operational and maintenance (O&M) due to the addition of these components, the attractive economic performance of the cycle reduces the annual fuel costs and offsets the increase in capital and O&M costs.

© 2022 Elsevier Masson SASAxial turbines are machines widely used in different engineering applications. Due to their constructive characteristics, they must have a space between the rotor blades and the turbine casing, called tip clearance. Unfortunately, this gap allows a part of the fluid to leak from the pressure side to the suction side of the rotor blades. This leakage is undesirable and represents an energy loss. A way to avoid part of this loss is through the use of desensitization techniques. Although the use of these techniques is widely known, no studies in the open literature have evaluated these techniques in hydraulic turbines. This work presents a numerical analysis of squealer desensitization techniques applied in a hydraulic axial turbine. The turbomachine under study is the first stage of the hydraulic axial turbine used in the Low Pressure Oxidizer Turbopump (LPOTP) of the Space Shuttle Main Engine (SSME). Numerical simulations were performed using CFX v.19.2 software, and computational meshes were generated in ICEM v.19.2 software. Initially, the computational model was validated, using the experimental results published by the National Aeronautics and Space Administration (NASA). A parametric analysis was performed considering the variation in squealer cavity depth and rim thickness. The study found that the squealer cavity depth has a greater influence on the stage performance than its rim thickness. The tendency is that the greater the cavity depth, the greater the stage efficiency. One of the squealer geometries analyzed allowed an average increased efficiency of 1.43%, over the entire turbine operational range. The results obtained also show that the application of the proposed geometries would enable the reduction in cavitation close to the trailing edge of the rotor blades. This result is extremely valuable, as it can impact the life cycle of the turbine.

© 2021 Elsevier Inc.The present work describes the implementation of an implicit time-integration numerical scheme to solve viscous flows in an in-house CFD solver. The scheme is developed to calculate engineering problems involving compressible flows. This work extends the defect-correction technique for the 3D flow calculations, and all mathematical formulations are described. The CFD solver is based on the finite-volume method (FVM) to calculate the three-dimensional flow and can be applied to solve unstructured meshes. The current implementation uses the Flux-Difference Splitting method (FDS) developed by Roe combined with the MUSCL method and the Venkatakrishnan flux limiters to provide better accuracy of the numerical solutions. The implicit time-integration scheme was linearized applying the backward Euler method on the left-hand side (LHS) and a Newton-type linearization on the right-hand side (RHS) of the governing equations. The Jacobian matrix was computed analytically for the inviscid fluxes using the Roe fluxes, and for the viscous fluxes differentiating the conservative vector. Earlier work by Cavalca et al. (2018) showed the robustness and accuracy of this implicit solver to predict inviscid flows over the airfoil and into the supersonic nozzle. Finally, the Gauss-Seidel (GS) iterative method was applied to solve the resultant sparse and large system of equations. These numerical schemes and methods were applied to solve the laminar flow over a flat plate. Afterwards, the numerical solution was validated and verified with the exact Blasius solution. From the results, the numerical simulations exhibited superior robustness of the implicit-defect correction scheme when compared with the explicit scheme for compressible flows. All numerical particularities and their implementations are detailed in this paper.

© (2022) by International Council of Aeronautical Sciences (ICAS) All rights reserved.Variable cycle engines promise to enable adaptive cycles that give close to optimal performance over a wide range of conflicting mission requirements, such as low altitude high speed flight and supercruise still providing excellent range. Modelling such engines pose challenges for general purpose software since variable geometry gas paths modify the underlying set of equations being solved. It is possible to use multiple engine models transferring design data between the models. This, however, creates a high risk for inconsistency and modelling error. It is more attractive if the solutions obtained could be determined using the same model. In this work an in-house software was developed to model an Adaptive Cycle Engine (ACE). This development was used to show how variable cycle mode switches can be integrated into general purpose performance tools. The variable cycle engine uses a FLADE, which is a "fan on blade" component, to extend its range and to provide improved subsonic performance. The individual impact of the components, its effect on propulsion performance parameters and in the engine installation were analyzed as the main results. The contribution from this paper is thus two-fold, firstly the paper goes ahead and proposes new methods for the simulation of mode switching in generic performance tools by introducing dynamic equation systems. Secondly, the paper then studies the FLADE component and its potential performance benefits if added to a conventional turbofan architecture.

© (2022) by International Council of Aeronautical Sciences (ICAS) All rights reserved.An Axial Turbine Blade Tip has a great influence on its flow behavior and performance. Due to the clearance between the turbine casing and the rotor blades tips, part of the flow leaks from the pressure side to the suction side. This leakage reduces the turbomachine efficiency, and therefore must be minimized. Over the years, the use of desensitization techniques has proven to be an excellent strategy for reducing this unwanted flow. These techniques, however, has only been studied in machines that operate with compressible fluids. The objective of this work is to verify the effects of two Winglet geometries in the first stage of the Liquid Oxygen (LOX) Turbine used as booster in the Space Shuttle Main Engine (SSME). The two Winglet geometries evaluated have identical thickness and width, being differentiated by their trailing edge region configuration. In this region, the first geometry (W1) connects to the trailing edge with an angle close to 90°, while the second geometry (W2) presents a smooth connection. The results obtained show that it is possible to improve the stage efficiency depending on the geometry adopted, as well as to analyze the cavitation phenomenon. The mesh generation and simulations were done using a commercial software and the 3D flow calculations were based on the Reynolds Averaged Navier-Stokes (RANS) equations.

Copyright © 2022 by ASME.The gas turbine industry requires extensive knowledge in several areas of engineering, and since both industry and academy continuously develop new approaches, technologies, and models, usually, there is not enough time to cover all the relevant subjects in one or two-semester courses for undergraduate or graduate students. In previous work, the authors have presented an interactive platform for the preliminary design of single-stage axial turbines with uncooled blades, for use at the undergraduate courses offered by the Turbomachine Department at Aeronautics Institute of Technology to accelerate the learning process. The present work aims to present an expansion of this interactive learning platform, with the inclusion of a module for the thermodynamic cycle study, a module for off-design calculations, and the generation of a PDF file containing the step-by-step solution memorial with all the equations and values used in the design. The work also presents a structure for the conduction of a graduate course in turbomachines focused on the design of axial turbines. It comprehends theory and exercise classes, oriented study with the interactive learning platform, and a project in which the students have to implement some of the modules and run test cases. The authors observed more interest of the students and higher quality questions in the classes while using the interactive platform or programming, developing a better understanding of the design process until the end of the course. Also, while, in previous semesters, the preliminary design occupied almost half of the 48-hour course, it took only 12-hour to cover the same subject, granting time to more advanced topics, such as blade cooling, off-design performance and computational fluid dynamics simulations.

Copyright © 2022 by ASME.Passive wall treatments with circumferential grooves in axial compressors proved to be effective in increasing the compressor stall margin in previous researches by creating a resistance to the flow that leaks in the tip clearance region of the compressor, from the rotor blade pressure side to the suction side. In the present work, a passive wall treatment with circumferential grooves was implemented in a multi-stage axial compressor. Different configurations of circumferential grooves were created at the casing of the first rotor row used in a four-stage axial flow compressor. 3D CFD flow simulations were performed in order to evaluate all the specified configurations aiming to find improvements on compressor stall margin. Investigations on the compressor flow characteristics were realized and the stall margin variations were determined. The numerical simulations were performed based on the Reynolds-Averaged Navier Stokes equations and the turbulence model was the k-ω SST. After the simulations, several rotational speeds of the compressor map characteristics, including the design-point rotational speed, were obtained for the case without casing treatment (smooth wall case) and for the case with circumferential grooves. In the results, passive wall treatment with circumferential grooves demonstrated an improvement in the compressor stall margin, especially for N=0.60 and N=0.90 rotational speeds.

© 2022, American Institute of Aeronautics and Astronautics Inc, AIAA., All rights reserved.This work investigates the use of solid and permeable surfaces in the Ffowcs WilliamsHawkings (FW-H) analogy for predicting high-speed propeller noise. The CFD/CAA methodology encompasses unsteady Reynolds-Averaged Navier-Stokes simulations to compute the flowfield on the acoustic surface applied in the FWH analogy to obtain the noise signatures in the far-field. Furthermore, this manuscript also investigates the effects of the downstream end-cap position, on the propeller noise prediction, by using two permeable surfaces with different lengths to assess the propeller noise levels in each case. The former is a short SFW-H surface placed near the rotor, and the latter, namely the LFW-H, is a surface larger in length where the end-cap grid is placed farther downstream from the rotor. The results showed the capability of the permeable surface technique for predicting the noise with higher accuracy than the solid formulation, especially at the first blade passing frequency. Also, the larger LFW-H surface performed better than the SFW-H surface. A reason that could justify this is that the LFW-H end-cap surface is placed at a suitable distance downstream from the propeller. Therefore, the LFW-H surface can include more of the contributions of the non-linear effects or quadrupole sources enclosed within the permeable source surface region.

© 2022, American Institute of Aeronautics and Astronautics Inc.. All rights reserved.Waste heat recovery is a key pathway to achieving reduced emissions and improved system efficiency. Waste heat can potentially be converted to electric power by several methods. One of the most effective methods is based on using a supercritical CO2 waste heat recovery power system. The sCO2 power system has advantages because of component compactness, which is an important consideration for aircraft integration. The present work focuses on implementing the supercritical CO2 power system into both current and next-generation aircraft engines that may use different fuels, such as hydrogen, ammonia, or sustainable aviation fuel (SAF). The first part of the work is focused on detailed optimization of the sCO2 waste heat system for a real aircraft engine with two sCO2 cycle configurations. The second part of the work is focused on detailed design of the heat exchangers, including weight and pressure drop calculation. The simulation was done using an in-house computer program for gas turbine performance and for the sCO2 cycle. The results show the potential utilization of waste heat in different operational regimes: idling on the ground, cruise, landing, and takeoff. One engine (nominal thrust of 9kN) with two different waste recovery units are investigated. The results demonstrated that the waste heat unit could generate an additional 100-200 kW for the 9-kN-engine (under cruise operation), which may reduce fuel consumption, even if the sCO2 system weight is around 800 lbm / 364 kg.

© 2021 Elsevier LtdThe requirements of Liquid Propellant Rocket Engine (LPRE) are high for thrust, specific impulse, and flow rate; thus, its components also have strict requirements. For the turbopumps (TPs), this means high flow rate, high rotational speed, and high pressure ratio, which makes their operations susceptible to the cavitation phenomenon, as observed in two previous works. In the first, cavitation regions were observed in the first stage of the Space Shuttle Main Engine (SSME) Liquid Oxygen (LOX) booster turbine, for 3.0, 5.5, and 8.0% tip clearances (relative to rotor blade height), using monophase flow (Lindquist Whitacker et al., 2017). In the second, the simulations were performed with multiphase flow, producing results more physically coherent for the 3.0% gap configuration (Whitacker et al., 2018). The characteristics of both types of simulations in space propulsion applications still require better understanding. Therefore, to compare monophase and multiphase results at various operating points and turbine configurations, steady-state turbulent 3-D Computational Fluid Dynamics (CFD) simulations were performed, based on Reynolds-Averaged Navier-Stokes (RANS) formulation. The same three tip configurations for the turbine first stage were simulated, and the calculations were validated using experimental results from the National Aeronautics and Space Administration (NASA) (Boynton and Rohlik, 1976). This made it possible to verify the effect of the tip clearance on the machine performance and internal flowfield. When the gap increased, the pressure loading decreased in a large region of the blade tip, the interaction was greater between the Tip Clearance Vortex (TCV) and a vortex generated around the shroud cavitation region (Cavitation Vortex - CV), and this interaction moved towards the middle of the blade-to-blade passage. Thus, the losses increased and the efficiency decreased. Various comparative aspects between the simulations using both mono and multiphase numerical schemes are also discussed.

© 2024, ETA-Florence Renewable Energies. All rights reserved.The green hydrogen industry is gaining momentum globally as a carrier of clean, sustainable energy with the potential to significantly reduce greenhouse gas emissions. Brazil, with its vast renewable energy resources and commitment to decarbonization, is emerging as a promising player in the green hydrogen market. As Brazil’s green hydrogen infrastructure expands, ensuring the safety and reliability of pipelines and accessories becomes crucial. This research provides an overview of the state of the art in pipeline and accessory inspection processes in the green hydrogen industry in Brazil, highlighting the advances and challenges faced in this rapidly evolving sector. It can also contribute to a better understanding of current knowledge about inspections in the green hydrogen transport network and how the collaboration of actors involved in the process of building international and national scientific knowledge is being carried out.

© 2023 by the authors.The aim of this paper is to evaluate the energy self-sufficiency of the tyre pyrolysis process using the pyrolysis gas produced as a heat source. Experimental data on the properties of the tyre and the main pyrolysis products (char, pyrolysis gas, and condensable vapours) have been compiled for a pyrolysis temperature range from 698 to 848 K. The laws of thermodynamics were used to calculate the energy demand of the tyre pyrolysis process, which was divided into heat for the pyrolysis reaction and heat transferred to the carrier gas. The pyrolysis gas was composed of 15 components, and its composition was calculated using a nonstoichiometric equilibrium model. For the temperature range studied, the heat required for the pyrolysis reaction was between 1.41 and 2.16 kJ/g of tyre. In addition, hydrocarbons (71 to 73 wt.%) were the major components in the calculated pyrolysis gas composition. An average lower heating value of 37.3 MJ/kg was calculated for the pyrolysis gas. The heat required for the tyre pyrolysis reaction was provided for burning 30–50% of the pyrolysis gas produced, thus making it self-sustaining. Energy self-sufficiency may not be achieved if the heat losses due to poor reactor insulation are high. However, this problem can be overcome by heating the combustion air using the heat released by the pyrolysis products during cooling.

© 2023 by the authors.This paper discusses the performance characteristics of a paraffin-based blend of liquid ethanol with paraffin as compared to pure paraffin in a hybrid rocket motor. Since the disclosure of the high regression rates of liquefying fuels as compared to classic fuels such as hydroxyl-terminated polybutadiene (HTPB), many studies using paraffin have been reported in the literature. Although pure paraffin regresses three to four times faster than HTPB, it is not an ideal fuel for launcher applications for the following reasons: it does not provide the optimum mechanical strength, it may suffer from combustion instability, and it offers low combustion efficiency. The proposed blend is biphasic, with drops of liquid ethanol trapped in a paraffin binder; and a nonionic surfactant was employed to emulsify the ethanol into paraffin wax. The results indicated that at a mean prefiring O∕F of 0.6 and a Gox of 60, both the P95E05 and P90E10 fuels demonstrated no significant statistical difference compared to pure paraffin in terms of thrust, specific impulse, fuel mass flow rate, characteristic velocity, and combustion efficiency. However, the P95E05 and P90E10 fuels did show damping in the pressure oscillations relative to paraffin, indicating a reduction in the low-frequency combustion instability observed in the ballistic responses of paraffin.

© 2023, The Author(s), under exclusive licence to The Brazilian Society of Mechanical Sciences and Engineering.Tire pyrolysis oil (TPO) shows promise as alternative fuels, not only for the raw material from which they can be produced (waste tires), but also their physical characteristics. In this work, the atomisation quality of TPO and its blends with diesel oil was evaluated from a statistical perspective. A 35 kW Y-jet atomiser, operating at an air-fuel mass ratio (AFR) in the range of 0.075 to 0.150, was used to produce the fuel sprays. The Log-Normal density function was used to describe the droplet size distribution of the sprays. Additionally, the d2-law was integrated into the density function to simulate TPO spray evaporation. The results showed that the increase in TPO in the fuel blend decreased the uniformity of droplet sizes in the spray, as well as increased the presence of larger droplets. However, operating the atomiser at a AFR = 0.150 reduced the presence of larger droplets and increased the volume fractions of smaller droplets.

© The Author(s), under exclusive licence to Springer Nature B.V. 2024.This paper is concerned with the robust position and attitude control of fully actuated fixed-wing multirotor aerial vehicles in the presence of disturbances and model uncertainties. To address this problem, we formulate the system using the vehicle’s nonlinear equations of motion considering the aerodynamic effects of the fixed wing as an additional disturbance. Then, we propose disturbance-observer-based attitude and position control laws using hybrid prescribed-time algorithms to control the vehicle and estimate model uncertainties and disturbances in two stages. In the first stage, the aforementioned algorithms employ nonautonomous formulations to ensure the convergence of the tracking and estimation errors to the origin in a prescribed time interval. Subsequently, in the second stage, the algorithms assume autonomous formulations to ensure robust stability of the errors over the infinite time domain. The proposed method is numerically evaluated, showing to be effective in providing the prescribed-time convergence of the tracking errors to zero and keeping them there afterwards.

© 2024 John Wiley & Sons Ltd.This paper is concerned with the prescribed-time robust attitude determination (AD) of multirotor aerial vehicles (MAVs) using vector measurements from the local magnetic field and local gravity. To address this problem, we first introduce a novel modified super-twisting algorithm endowed with the prescribed-time convergence property. The (Formula presented.) state of the proposed algorithm is governed by an unbounded time-varying gain up to the prescribed settling time (PST) and by a (Formula presented.) function after that. Therefore, after the PST, the new algorithm coincides with the conventional super-twisting, thus showing robust stability at the origin. This prescribed-time super-twisting algorithm (PTSTA) is then applied to the formulation of a three-stage gyro-free attitude determination method for MAVs. In the first stage, the classical QUEST algorithm is used to compute a Wahba-optimal attitude estimate from the vector measurements. In the second stage, the PTSTA is employed in the formulation of a robust state estimator that provides estimates of the attitude Gibbs vector and its rate. Finally, in the third stage, these state estimates as well as the attitude kinematic equation are immediately used to compute the MAV angular velocity. The proposed robust prescribed-time gyro-free AD method is evaluated numerically, showing invariance with respect to disturbance and model uncertainty.

© The Author(s), under exclusive license to Springer Nature Switzerland AG 2025.This chapter explores advancements in achieving stability within prescribed convergence time constraints. Drawing from the evolution of stability concepts, including finite-time stability (FTS), fixed-time stability (FxTS), and predefined-time stability (PTS), the chapter presents strategies to address the limitations of traditional FTS methods. Furthermore, it introduces a novel two-stage super-twisting algorithm (STA) that ensures robust prescribed-time state convergence by employing both time-varying and switching gains. By tuning these gains, we guarantee that the proposed algorithm’s analytic solution robustly reaches the origin exactly at the prescribed time. Numerical simulations involving a state-observer-based control problem for a perturbed damped pendulum validate its performance. The results show that the estimation errors converge robustly to the origin at the prescribed instants and remain there afterward. Moreover, a second-order sliding mode is obtained for the controller, driving the tracking errors asymptotically to the origin.

© Brazilian Society for Automatics--SBA 2024.This paper is concerned with the translational guidance of multirotor aerial vehicles with uncertain dynamics and equipped with short-range detection sensors in a scenario containing disturbances/uncertainties, multiple accelerated obstacles, and velocity constraints. To address this problem, we propose a robust guidance strategy based on the continuous control obstacles method. To handle disturbances and uncertainties, the proposed method tightens the position and velocity admissible sets according to the respective tracking errors. Moreover, a hybrid prescribed-time arbitrary-order differentiator is employed to robustly estimate the obstacles’ velocities and accelerations within a prescribed time interval using measurements from a short-range sensor. As a result, the proposed method can fit into the available time for executing an avoidance maneuver upon the detection and tracking of obstacles. Then, we build a set of possible future positions for the obstacles according to their observed velocities and accelerations, and use this set to calculate a position command for the guided vehicle. The proposed method is experimentally evaluated using an augmented-reality setup composed of a Crazyflie quadcopter, motion capture cameras, and virtual obstacles. The results show that the proposed method is viable for real-time implementation and effective in providing collision avoidance and satisfying velocity constraints.

© The Author(s), under exclusive licence to The Brazilian Society of Mechanical Sciences and Engineering 2024.This paper is concerned with the design and analysis of the three-dimensional attitude control law of an arbitrary underactuated multirotor aerial vehicle with a fully actuated three-axis attitude motion subject to bounded matched disturbances and uncertainties, both with unknown bounds. To tackle the problem, the rotational kinematics and dynamics of the attitude and angular velocity control errors are first modeled in a geometrically consistent form using the Gibbs vector. Then, we formulate a multi-input adaptive sliding mode control strategy, of the unit-vector type, based on an increasing switching-gain adaptation law. The adaptive switching gain is proved to converge to its maximum bound, even in the presence of sufficiently small chattering, and the existence of an eventual sliding mode is assured. The method is extensively evaluated by simulation considering an X-shaped octa-rotor aerial vehicle. It is also demonstrated experimentally using a three-axis hover that emulates a quadrotor aerial vehicle.

© 2024 IEEE.This paper deals with the robust prescribed-time nonlinear state estimation for fusing multiple redundant noisy sensor measurements. Firstly, we present the prescribed-time super-twisting algorithm (PT-STA), which is a recent modified version of the classical super-twisting algorithm that ensures robust convergence within a prescribed time. Subsequently, the PT-STA is used to design a prescribed-time nonlinear robust state observer for second-order systems subject to disturbances and uncertainties. The observer is then combined with an average-based sensor fusion strategy that further improve the overall estimates in terms of noise rejection and sensor fault tolerance. We introduce sensor fusion algorithm for considering the availability of multiple redundant measurements. The effectiveness of the proposed scheme is illustrated via numerical simulations of a perturbed damped pendulum, under different numbers of measurements and also considering sensor fault. We compare the results with those obtained using the conventional super-twisting observer. The results indicate robust convergence of estimation errors to the origin within the prescribed time, a reduction in measurement noise as the number of measurements is increased, and sensor fault tolerance.

© 2024 IEEE.This paper proposes a robust guidance for mul-tirotor aerial vehicles with uncertain dynamics and equipped with short-range detection sensors in scenarios with multiple accelerated obstacles and velocity constraints. To handle the uncertain dynamics in the guidance level, the position and velocity admissible sets are tightened according to the respective inner-loop tracking errors. Moreover, a hybrid prescribed-time arbitrary-order differentiator is used to estimate the obstacles' velocities and accelerations using the sensor readings. Based on these estimates, we build a set of possible future positions for the obstacles, and use this set to calculate a robust collision-free position command for the vehicle. The proposed method is experimentally evaluated using a mixed-reality setup composed of a Crazyflie quad copter, motion capture cameras, and virtual obstacles. The results show that the proposed method is viable for real-time implementation and effective in providing collision avoidance and satisfying velocity constraints.

© 2024 IEEE.The control allocation of a quad copter with I-DOF vectoring thrust, respecting the rotors and actuators' physical bounds, is the subject of this paper. We start by assuming a hierarchical control architecture, where the control law gen-erates resultant force and torque commands to be distributed by the control allocation algorithm among the spinning and thrust vectoring motors. We define the control allocation as an optimization problem with the thrust vector components of each rotor being the design variables. By doing so, we obtain a set of constraints that depend linearly on the thrust vector magnitudes. The magnitude constraints can lead to a non-convex set when the rotors' minimum speed command is greater than zero. We tackle this issue by defining a conservative inferior limit to one of the thrust components in a way that the non-convexity is excluded from the resulting constraint set. To ensure the feasibility of the method, we state that the control effort commands outputted by the vehicle control law must lie within an admissible set of that optimization problem. Simulation results compared the proposed method with other control allocation strategies and showed that it is more effective in preventing violations of rotor constraints while achieving the required command of resulting force and torque.

© The Author(s), under exclusive license to Springer Nature Switzerland AG 2024.The present paper is concerned with the robust attitude-position tracking control for a formation of heterogeneous fully actuated multirotor aerial vehicles equipped with fixed rotors and subject to matched model uncertainties and Lipschitz disturbances. Based on a geometrically consistent description of the control error in SE(3), a joint geometric attitude-position control law is designed using a super-twisting sliding mode approach. Trajectory commands for the formation are generated using a second-order polynomial S-curve model, which are designed in such a way that allow setting different time duration for the formation acquisition, position, and attitude commanded motions. The method is evaluated via numerical simulations using a formation of non-planar fully actuated hexacopters equipped with fixed rotors, showing to be effective and simple to implement and tune.

© The Author(s), under exclusive license to Springer Nature Switzerland AG 2024.This work is concerned with the attitude and position control of a fully actuated non-planar hexarotor aerial vehicle equipped with reversible fixed rotors. The complete nonlinear dynamics of the vehicle is modeled in a state error formulation with six degrees of freedom (DOF), being three for position and three others for attitude, while the control input is also a six-DOF quantity defined in terms of the resultant force and torque acting on the system. A control law is designed using an unit-vector global sliding mode control strategy, which ensures robustness against bounded force and torque disturbances during the entire flight since the sliding condition is guaranteed from the initial time. Furthermore, the proposed controller also ensures global exponential stability for both the closed-loop translational and rotational dynamics. Using computational simulations, the designed control law is compared with an inverse-dynamic stabilizing control, showing to be effective and to perform much better.

© 2013 IEEE.This paper addresses the robustness of a novel two-stage super-twisting algorithm designed to converge within a prescribed time interval despite disturbances and model uncertainties. Initially, we introduce a method for tuning parameters that guarantees the algorithm's analytic solution will reach the origin precisely at a prescribed instant, assuming an unperturbed scenario. We then enhance this method to maintain prescribed-time convergence, even when faced with unknown bounded disturbances. The algorithm's performance is demonstrated through a numerical simulation of a state estimation problem for a perturbed damped pendulum. The results show that the estimation errors converge robustly to the origin at the prescribed time and remain there afterward.

© 2013 IEEE.This paper is concerned with the attitude and position control of underactuated multirotor aerial vehicles in the presence of matched disturbances and uncertainties, using the hierarchical scheme that nests the attitude control loop inside the position one. It is well-known that the effectiveness of this scheme depends on a proper control tuning for achieving a sufficient time-scale separation (TSS) between the closed-loop (faster) rotational and (slower) translational dynamics. However, a TSS cannot be ensured under an ideal sliding mode position control law since the attitude command, computed from the position control signal, is infinitely fast. The present paper tackles this problem in a way to enforce TSS without losing robustness and using a dull trial-and-error tweak of gains. That is achieved by designing, on the one hand, a new adaptive integral sliding mode attitude control law (AISMAC) that, under a sufficient smooth attitude command, ensures the existence of an attitude sliding mode during all the time, including the adaptation phase, thus allowing an infinitely fast inner loop. On the other hand, the outer loop is equipped with a disturbance-observer-based proportional-derivative position control law that ensures the required smoothness of the attitude command and provides robustness with respect to unknown force terms. The proposed design is extensively evaluated in a realistic simulator and shows to effectively enforce the TSS.

© 2023, The Author(s), under exclusive licence to Springer Nature B.V.This paper is concerned with the robust guidance and control of fully actuated multirotor aerial vehicles in the presence of moving obstacles, linear velocity constraints, and matched model uncertainties and disturbances. We address this problem by adopting a hierarchical flight control architecture consisting of a supervisory outer-loop guidance module and an inner-loop stabilizing control one. The position and attitude control laws are designed using a proportional–derivative approach combined with a high-order sliding mode disturbance observer. The resulting inner-loop control strategy is arbitrarily smooth and robust (in the sliding mode sense) with respect to model disturbances and uncertainties. On the other hand, we propose a robust collision-free guidance strategy that extends the continuous-control-obstacles method to drive the vehicle to a target pose under velocity constraints, disturbances, and uncertainties, in an environment containing moving obstacles. The overall method has been numerically evaluated and shown to be effective in providing satisfactory tracking performance, collision-free guidance, satisfaction of linear velocity constraints, and computational viability. Furthermore, it is shown to outperform an analogous scheme based on the original continuous-control-obstacles method and conventional sliding mode inner-loop control laws.

© 2023 by the authors.This paper is concerned with the robust collision-free guidance and control of underactuated multirotor aerial vehicles in the presence of moving obstacles capable of accelerating, linear velocity and rotor thrust constraints, and matched model uncertainties and disturbances. We address this problem by using a hierarchical flight control architecture composed of a supervisory outer-loop guidance module and an inner-loop stabilizing control one. The inner loop is designed using a typical hierarchical control scheme that nests the attitude control loop inside the position one. The effectiveness of this scheme relies on proper time-scale separation (TSS) between the closed-loop (faster) rotational and (slower) translational dynamics, which is not straightforward to enforce in practice. However, by combining an integral sliding mode attitude control law, which guarantees instantaneous tracking of the attitude commands, with a smooth and robust position control one, we enforce, by construction, the satisfaction of the TSS, thus avoiding the loss of robustness and use of a dull trial-and-error tweak of gains. On the other hand, the outer-loop guidance is built upon the continuous-control-obstacles method, which is incremented to respect the velocity and actuator constraints and avoid multiple moving obstacles that can accelerate. The overall method is evaluated using a numerical Monte Carlo simulation and is shown to be effective in providing satisfactory tracking performance, collision-free guidance, and the satisfaction of linear velocity and actuator constraints.

© 2023, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.Real-time fluid engineering simulations require significant computational power and high-resolution grids to ensure accuracy. This paper proposes a novel CUDA-C-based simulation algorithm nemesys that leverages GPU devices to solve the Navier-Stokes equations with precision and speed. The algorithm uses a Successive Over Relaxation (SOR) iterative process on a multi-dimensional CUDA core to accelerate solving speed. The co-located Rhie and Chow interpolation scheme is applied to unstructured grids to solve the equations using an implicit finite volume method. Benchmark simulations are performed on two problems aimed to validate the effectiveness of the proposed methodology: the classical lid-driven cavity and closed-channel flow. Results exhibit a significant advantage of the proposed method in terms of convergence rate compared to state-of-the-art techniques using varying grid resolutions and Reynolds numbers. Specifically, the strategy is nearly 850 times faster than parallel CPU-based code when utilizing an RTX 3090 Nvidia graphics card. Furthermore, the algorithm's performance is investigated on an airfoil simulation, confirming the approach's effectiveness. The findings highlight that GPU-based parallel programming is a promising approach for achieving realtime simulations, and the proposed algorithm presents a significant improvement over CPU-based techniques.

© 2017 IEEE.This letter is concerned with the collision avoidance for mobile robots with uncertain dynamics in the presence of obstacles that can considerably change their velocities over time. To address this problem, we propose a robust collision-avoidance method based on the continuous-control-obstacles one. The proposed method uses an arbitrary-order overdamped low-pass filter to generate sufficiently smooth position commands for the robot and a high-order sliding mode differentiator to robustly estimate the obstacles' maximum accelerations. Based on these estimates, we define a set of possible future positions for the obstacles according to how each one is changing its velocity to calculate a robust position command for the robot. The method has been numerically evaluated using a conventional quadcopter flying among moving obstacles and has been shown to be effective in providing collision avoidance and velocity constraints satisfaction.

© 2013 IEEE.The ability of multiple manned and unmanned aircraft systems to cooperatively engage and disable an aerial threat plays a decisive role in modern warfare scenarios. In this paper, we apply key methods to enable the so-called cooperative threat engagement capability among multiple networked agents, e.g., a swarm of drones, with combat and communication capabilities. In particular, this research combines AI-based decision-making and control techniques for a swarm of loyal wingman drones to coordinate efficient defense actions in a cooperative and autonomous manner. We apply these concepts in a defense scenario that is modeled to analyze the loyal wingman concept, which we consider an interesting testbed for cooperative decision-making and low-level control techniques. The investigated methods were implemented in a realistic 3D UAV simulator for demonstration and evaluation.

© 2022 ISAThe present paper is concerned with the robust and smooth attitude-position tracking control of fully actuated multirotor aerial vehicles equipped with fixed rotors and subject to matched model uncertainties and disturbances. The vehicle coupled dynamic equations representing the translational and rotational motions are thoroughly derived using the multibody approach, considering the external torque and force disturbances as well as the uncertainties in the inertia parameters of the airframe and the rotors. From this model, it is shown that the overall disturbances and uncertainties can be lumped into an additive-matched plant-model discrepancy. Then, based on a geometrically consistent description of the control error in SE(3), a novel joint geometric attitude-position control law is designed using a multi-input smooth second-order sliding mode strategy. The latter uses a high-order sliding mode disturbance observer to guarantee the overall system robustness. The second-order sliding mode is proved to exist using vector-field homogeneity, and the tracking error is shown to exponentially converge to the origin. The method is extensively evaluated via numerical simulations using a fully actuated hexacopter with tilted rotors, showing advantages with respect to state-of-the-art alternatives.

© 2021 ISAThe present paper is concerned with the wayset-based guidance of underactuated multirotor aerial vehicles (MAVs). A hierarchical guidance and control structure is first established, in which the guidance is realized as a supervisory loop. The lower-level stabilizing attitude and position control laws are assumed to be available. On the other hand, the outer-loop guidance is designed based on a fixed-horizon tube-based robust model predictive control (MPC), which conducts the MAV to visit a given sequence of waysets, without violating their state and control bounds, and allowing the vehicle to rest in each wayset for a specified period. The MPC is designed using a reduced-order closed-loop dynamic model describing the vehicle's translation, which is derived considering the stabilizing position and attitude control laws and the assumption of a time-scale separation between the closed-loop translational and rotational dynamics. This model is put into a discrete-time linear state–space representation subject to additive bounded random disturbance and measurement noise. The properties of the proposed method, which includes the MPC recursive feasibility and robust stability as well as the overall guidance feasibility, are analytically studied. The method is also numerically evaluated using a realistic quadrotor dynamic model, showing its effectiveness and confirming its properties.