© 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.

© 2025 Author(s).The present work explores a bio-inspired modification of a cylinder, incorporating a wavy pattern inspired by humpback whale flipper tubercles. Drawing on prior research on airfoils and wings, the investigation provides valuable insights into the implications of this novel geometry on cylinder flow, contributing to the existing knowledge in the field. A selection of four patterns of waviness (varying in amplitudes and wavelengths) is compared to a smooth (i.e., straight cylinder) model by measuring pressure distribution and aerodynamic forces. The study is conducted in a wind tunnel, considering Reynolds numbers from about 3.9 × 10 4 to 1.9 × 10 5 . Notable findings include a drag coefficient reduction of up to 25% for a model with 12% wavelength and 3% waviness amplitude. Flow visualization reveals the presence of two distinct phenomena: the formation of three-dimensional laminar separation bubbles, and the indications of counter-rotating vortex pairs over the cylinder surface. These flow structures contribute to explain the observed drag variation through changes in the separation line, base pressure, and other associated mechanisms. This study enhances our understanding of the performance of such bio-inspired designs.

© 2025 by Geovana Neves.This paper introduces the Standard Model ITA (SMI), an interchangeable aircraft model framework designed to investigate aeropropulsive integration of propellers in support of future sustainable aviation applications. Early design phases progress rapidly, requiring streamlined methods to capture aeropropulsive effects from high-level parameters within product development time constraints. Designed as a generic approach, the methodology can integrate aerodynamic data from theoretical models and wind tunnel tests (WTT), leveraging information at the integrated coefficient level to support quick comparative analysis. The method focuses on longitudinal characterization, describing the local angle of attack and dynamic pressure at the horizontal tail using 3D-equivalent parameters. For rear-mounted configurations, the same procedure enables the calculation of averaged propeller slipstream swirl and dynamic pressure effects at the pylon, while installed propeller inflow angles are determined via in-plane force analysis. The aerodynamic evaluation of the SMI platform was carried out using CFD RANS simulations for power-off conditions, with further characterization in poweron conditions using Flightstream®, a panel method solver. The wing-mounted configuration (SMI-L1) exhibits a significant reduction in static stability in powered conditions, whereas rear-mounted configurations (SMI-L2 and SMI-L3) are inherently more stable concepts. This research provides a structured methodology for incorporating aeropropulsive effects early in the design cycle, enhancing aircraft sizing efforts and supporting sustainable aviation objectives.

© 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.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.

© 2022 by the authors.A numerical investigation is proposed to explore the flow past a novel wavy circular cylinder as a passive flow control, whose shape is determined by a sinusoidal function applied to its leading edge line, similar to studies with wavy leading-edge airfoils. The latter are motivated by the wavy-shaped tubercles found in the flippers of humpback whales, which are believed to improve their maneuverability. Our attempt is, therefore, to assess the effects of leading-edge waviness now on a simpler and canonical geometry: circular cylinders. The present work relies on iLES simulations conducted with Nektar++ at a Reynolds number of 3900. Besides the straight cylinder, two wavy geometries are assessed, which are determined by a single wavelength of 37.5% for two amplitudes, 3% and 11%, based on the mean diameter of the wavy cylinder. Our results showed that, contrary to what is usually the case with traditional wavy cylinders at similar Reynolds numbers, waviness caused a reduction in the near-wake recirculation length and an increase in the mean near-wake turbulent kinetic energy compared to the straight cylinder. This was followed by a reduction in base pressure (up to about 36%) leading to a rise in lift oscillations and also to a significant increase in the mean drag coefficient of up to about 28%. An attempt to detail the flow phenomena is provided, evidencing the emergence of counter-rotating pairs of streamwise vortices between peaks. It is argued that the differences observed in recirculation length, turbulent kinetic energy, and force coefficients start even prior to the formation of these coherent structures and end up with interactions with the near wake.

© 2022 International Astronautical Federation, IAF. All rights reserved.A blowdown liquid fuelled rocket engine (LRE) survey, propelled by commercial hydrogen peroxide (CHP) and automotive ethanol, is presented. The main objective of this engine is to have a low-cost technology demonstrator to be used in a prototype of a training rocket for the Alcantara Launch Centre. In a LRE, the injector is an essential component since it is responsible for providing an efficient atomization and a stable burning in the combustion chamber. The complete decomposition of the pure hydrogen peroxide (H2O2) produces gaseous oxygen and water vapor. In this case, the commercial CHP is a 50% H2O2/50% H2O mixture. As there is much water in this mixture, a great part of the decomposition heat is absorbed by the water that remains after the catalytic bed. A crossover occurs at 63-64% mixture, when rapid, accelerated decomposition becomes self-sustaining. Different methods to model two-phase flow on a horizontal pipe have been studied: The homogeneous model, which, in a general fashion, the liquid and gas move at the same velocity; The separated flow model (SFM) that considers that both phases flow separately in the pipes; And the dimensional and similitude analysis. As the studied component is an injector (almost isentropic) composed by different subcomponents, the SFM is used. The sum of the area occupied by each of the phases must be the internal area of the injector, which are determined by the hydraulic diameter of each one (and) and the ratios (and) of the actual cross-section area of flow to the area of the hydraulic diameters. Furthermore, due to the all-transient characteristic of the blowdown, these hydraulic diameters are variable. In order to test and validate this blowdown LRE, a test bench was built using Commercial off-the-shelf (COTS) low-cost equipment compatible with the oxidizer. In addition, pressure transducers were installed to measure relevant data, regarding the decomposition produced, on the oxidizer tank as well as on the input/output of the catalytic bed. The results showed that the SFM is an appropriate solution to model this blowdown LRE and that for an accurate simulation, the Arrhenius parameters of the CHP with the catalyst must be determined by many tests.

© 2022, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.Flow over a humpback whale flippers bio-inspired wavy cylinder is experimentally investigated. Besides the smooth model, a selection of a set of 4 wave combinations (2 amplitudes x 2 wavelengths) is compared using pressure distribution and aerodynamic forces. The study is performed in a wind tunnel at Reynolds numbers ranging from 3.9 × 104 to 2 × 105, within the sub-critical regime. The most notable results show that, for the 12% wavelength, the 3% and 11% amplitudes have opposite effects, with a drag coefficient reduction of up to 25%, and an increase of up to 25%, respectively. Flow visualizations shows the formation of three-dimensional laminar separation bubbles and the action of counter-rotating vortex pairs, with a shift in the separation line and a change in the base pressure, which suggest the mechanisms behind drag variation.

© 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.