© 2026 The Author(s).Landfill gas (LFG) is a renewable yet highly diluted fuel whose variable composition and operation at elevated pressures pose significant challenges for stable and efficient combustion. In this work, the laminar burning velocity (LBV) and Markstein length of realistic CH4–CO2–N2 mixtures were investigated experimentally and numerically at 298 K, at pressures up to 5 bar, and for equivalence ratios ranging from 0.6 to 1.3, with special focus on the lean region where new burners concepts are expected operate and where data is quite scarce. Two surrogate fuels containing 65% and 55% CH4 were formulated while maintaining a constant CO2:N2 ratio to isolate the effect of total dilution. Experimental LBVs were determined using the outwardly propagating spherical flame method and compared with detailed chemical-kinetic mechanisms. Among the mechanisms evaluated, Konnov Mech 0.6 provided the best agreement with experimental data at 1 bar. The results show that increasing pressure and dilution both significantly reduce the LBV; however, they act through distinct mechanisms. Dilution primarily suppresses flame propagation through thermal effects, reducing adiabatic flame temperature and overall reaction rates, whereas pressure enhances competition between chain-branching and termination reactions, leading to reduced radical concentrations. Sensitivity and pathway analyses identified the reaction H + O2 ⇌ O + OH as the dominant promoting step controlling flame propagation under all conditions. The Markstein length was found to increase from lean to rich mixtures and to decrease with increasing pressure, indicating enhanced flame instability at elevated pressures. The present study provides new high-pressure experimental data and a detailed mechanistic interpretation of LFG combustion, contributing to improved modeling and the design of energy systems operating with low-calorific-value fuels.

© 2026 The Author(s).Sustainable aviation fuels (SAFs) are a critical pathway for reducing carbon dioxide (CO2) emissions from the aviation sector, yet the deployment of new SAF candidates requires a robust understanding of their fundamental combustion behavior. Limonene, a renewable terpene derived from pine and citrus biomass, has emerged as a promising candidate due to its favorable energy content and bulk properties relative to conventional Jet A-1. However, despite increasing interest, fundamental premixed combustion data for limonene—particularly laminar burning velocity and flame stability parameters—remain limited. The aim of this study is to address this gap through an experimental investigation of the premixed combustion characteristics of limonene. Laminar burning velocity measurements were performed in spherical and cylindrical constant-volume reactors at atmospheric pressure and unburned-gas temperatures of 358, 398, and 438 K using Schlieren imaging. Experiments were conducted for pure limonene, the Jet A-1 surrogate fuel MURI-1, and a 70/30 (vol./vol.) MURI-1–limonene blend over equivalence ratios from 0.7 to 1.4. The results show that pure limonene exhibits high laminar burning velocities, reaching peak values of approximately 70 cm s⁻1, exceeding those of conventional kerosene surrogates. Flame stability analysis reveals that limonene flames become increasingly sensitive to stretch under fuel-rich conditions, as indicated by decreasing Markstein length and Lewis number. Blending limonene with MURI-1 yields intermediate burning velocities and improves flame stability through increased Markstein length, despite a modest reduction in flame thickness, with enhancements of up to 8% observed under rich conditions. These findings provide new fundamental combustion data for limonene and demonstrate combustion trends consistent with other SAF candidates, supporting its potential as a viable component for future ASTM-certified sustainable aviation fuel formulations and for the development of validated chemical-kinetic models.

© 2026 IAA. Published by Elsevier Ltd. All rights are reserved, including those for text and data mining, AI training, and similar technologies.AbstractScramjet engines offer great potential for hypersonic propulsion and space access, but efficient combustion remains challenging due to the extremely short residence time for fuel–air mixing and burning. This study presents a parametric investigation of a cavity flameholder with upstream transverse hydrogen injection applied to the HyShot-IV scramjet combustor geometry, using RANS-based CFD simulations in Ansys CFX. The model incorporates the k[jls-end-space/]–ω SST turbulence model and the Burning Velocity Model to analyze the impact of cavity aspect ratio (AR) on key performance parameters, including mixing efficiency, combustion-chamber efficiency, flame stabilization, and pressure recovery. Six configurations were examined: one baseline without a cavity and five cavity cases with (Formula presented). Results demonstrate that cavity flameholders significantly enhance combustion performance by generating recirculation zones, stabilizing the flame, and intensifying turbulence, which collectively promote efficient fuel–air mixing, and these favorable effects are further amplified with increasing AR. Case E ((Formula presented) ) achieved the highest performance, with mixing and combustion efficiencies of 72.3% and 72.5%, respectively, at the expense of a moderate reduction in pressure recovery to 53.8%. Conversely, smaller cavities, such as in Case A ((Formula presented) ), provided limited mixing improvements, with a mixing efficiency of 55.9%, yet retained higher pressure recovery at 56.7%. Key flow features observed include shear layers, cavity expansion shocks, and counter-rotating vortex pairs (CVPs), which interact with shock waves and boundary layers to enhance fuel distribution and combustion. Larger cavities, such as in Cases D ((Formula presented) ) and E, promoted earlier hydrogen consumption and sustained combustion zones. The baseline configuration, lacking a cavity, exhibited the lowest performance metrics, with poor mixing efficiency (51.3%) and delayed combustion, underscoring the importance of cavity-induced structures for efficient scramjet operation.

© 2025 Elsevier LtdAs an effort to reduce energy demand, researchers have been exploring the use of ejector pumps on cooling, heating and recirculation systems. To increase the ejectors efficiency, several studies propose optimizing the entrainment ratio and pressure ratio using CFD-based surrogate models. However, no study attempted to include an outlet temperature constraint, and there is no consensus on which surrogate model to use, or how to improve the models accuracy. The main goal of this paper is to develop a high-accuracy surrogate model, used to find optimal ejector geometries, that consider three functions of interest: maximizing the entrainment ratio, on various pressure ratios, constraining the outlet temperature. The methodology was implemented for a supersonic air ejector pump used to heat an aircrafts compartment. This work explore the correlation between the ejectors geometry and the functions of interest, the prediction accuracy of ten surrogate models, and a refinement process that increases the models accuracy at the pareto front. The resulting Universal Kriging model provided geometries that complied with the outlet temperature constraint and improved the entrainment ratio by 11.6% and 108.1% for the pressure ratios of 0.97 and 1.05, respectively, when compared to a geometry from the literature.

© The Author(s), under exclusive licence to The Brazilian Society of Mechanical Sciences and Engineering 2025.The aircraft flying qualities are assessed during preliminary design phases through dynamic stability derivatives and an adequate accuracy is necessary to avoid costly fixes after flight testing. The dynamic stability derivatives estimation process uses unsteady CFD or dynamic data acquisition in wind tunnel testing, but both are very expensive. However, using the Navier–Stokes equations rewritten in non-inertial reference frame embedded in a CFD software it is possible to estimate dynamic aerodynamic coefficients using steady-state CFD, which is demonstrated in the present work with adequate accuracy for both 2D and 3D study cases.

© The Author(s), under exclusive licence to The Brazilian Society of Mechanical Sciences and Engineering 2025.Optimizing the energy conversion processes within aircraft and developing novel aircraft configurations have become imperative for fostering a more sustainable aviation sector. Exergy analysis emerges as a valuable tool in pinpointing areas for improvement and evaluating innovative configurations. The present work intends to expand upon the exergy concept in the assessment of airfoil aerodynamics. This is achieved through drag breakdown and flow field analysis utilizing the exergetic method. The study employs computational fluid dynamics analysis, utilizing the airfoil NACA 0012 for subsonic compressible flow and NACA 2315, NACA 2312, and NACA 2309 for transonic compressible flow as test cases to illustrate the concept. Rates of exergy destruction and a thorough flow field analysis are presented along the wake downstream of the airfoil, comparing four turbulence models. The theoretical exergy method is juxtaposed with the classical near-field method and validated through technical reports. Ultimately, the findings indicate a potential for improvement using the exergy method in aerodynamics, resulting in a 12% reduction in drag in a 2D flow field, translating into potential energy savings up to 31000 W. Furthermore, it is also demonstrated that the impact of airfoil thickness variation on exergy destruction in the transonic regime is found to be negligible.

© 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, Scipedia S.L., All rights reserved.Spectral element methods (SEM) are receiving increased attention over recent years given their capability to yield LES-type results without turbulence models (implicit LES - iLES). There is, though, a lack of fundamental studies on the suitability of continuous Galerkin (CG) methods, as most studies have focused on discontinuous SEM. This work aims to investigate solution quality and numerical robustness of CG-iLES by discussing simulations of the Taylor- Green Vortex and of spatially-developing turbulent channel flows. The performance of a recently developed stabilization technique (GJP) receives special attention. We show that CG-iLES with GJP can outperform traditional LES and be competitive alongside discontinuous SEM iLES.

© Springer Nature Switzerland AG 2024. All rights reserved.In-flight ice protection is typically performed by mechanical, chemical, thermal, or hybrid systems. One of the most traditional, cost-effective, and still often used techniques is hot-air anti-icing, which normally heats the interior of the affected aerodynamic surfaces with an array of small hot-air jets generated by a perforated tube (piccolo). These devices are designed to optimally distribute the energy along the protected area, ensuring that the local heat demand for anti-icing can be satisfactorily achieved. In this chapter, an example of a low-cost numerical model to resolve the compressible internal flow along the length of a piccolo is provided. The governing equations are those of the thermodynamic state of air, mass continuity, momentum, and energy conservation. The equations are used in algebraic form and are solved in sequential control volumes that are axially distributed along with the piccolo. At each orifice of the piccolo, the airflow is also treated in one dimension, with the intrinsic three-dimensionality of the air efflux being modeled with the help of a discharge coefficient correlation. A correlation can be based on experimental data, which is the case in the comparisons to the experimental results presented later in this chapter. This technique is quite efficient since it allows the prediction of the flow distribution along with a piccolo without demanding a high computational effort. As a direct benefit, for instance, the use of such low-cost models allows the analysis of multiple piccolo configurations before the selection of one for laboratory testing or production.

© 2023, The Author(s), under exclusive licence to The Brazilian Society of Mechanical Sciences and Engineering.Nowadays, numerical simulations of wind turbines based on the Reynolds-averaged Navier–Stokes (RANS) formulation are becoming, in terms of computational cost, increasingly more viable tools for geometry optimization and design. Nevertheless, a judicious use of RANS-type methods is still required to guarantee acceptable accuracy at manageable computational cost. Here, we assess the accuracy and cost of several well-known turbulence models (Spalart–Allmaras, k- ε , k- ω SST, along with transitional modelling) with and without a zigzag tape modelling for a representative horizontal axis wind turbine within a range of moderate Reynolds numbers (Re ≈ 3 × 10 5 to 8 × 10 5). This range allowed for the assessment of turbulence models under various complex flow conditions. Significant differences in performance have been found and, for a notable portion of the test cases, the k- ε model was able to deliver good results (similar to k- ω SST results) with a considerably coarser mesh. This suggests that k- ε , although often recognized as less accurate than k- ω SST, might actually be more efficient for wind turbine simulations. Also, although the best results came only with a coupled transition model which required a higher computational cost, this increase in cost is not exceedingly high and might allow for this model’s usage in later design stages. Accordingly, the present study is a valuable source for future wind turbine simulations and design and we hope that it fosters further developments in the field.