Validated Computational Analysis and Airfoil Optimization for Fixed-Wing UAV using XFLR5 and Boundary-Layer-Resolved CFD

Abstract

This study introduces a validated and systematic framework for the aerodynamic analysis and optimization of airfoils specifically designed for medium-altitude long-endurance (MALE) fixed-wing unmanned aerial vehicles (UAVs).  Seven airfoils—CLARK-Y, E-387, RG-15, MH-32, NACA 2415, NACA 23015, and NACA 4415—were evaluated at a Reynolds number of 1×10⁶ utilizing XFLR5, which is based on the XFOIL panel method. The NACA 4415 airfoil was identified as the optimal candidate for detailed high-fidelity analysis based on its lift-to-drag performance and stall characteristics. Subsequent Computational Fluid Dynamics (CFD) simulations were performed using ANSYS Fluent, utilizing the standard SST k–ω model, which assumes fully turbulent flow, alongside the SST-Transition model that integrates transition-sensitive transport equations to address the evolution of laminar-to-turbulent boundary layers.  The simulations enabled precise characterization of flow separation, boundary layer development, and post-stall aerodynamic behaviour over a wide range of angles of attack. Numerical results have been validated with experimental data obtained from the 3×5 ft and 7×10 ft subsonic wind tunnels at Ohio State University. The SST-Transition model demonstrated superior predictive accuracy, with deviations remaining within 10% during the pre-stall regime and closely aligning with post-stall trends. XFLR5 showed efficiency in initial airfoil screening; however, it significantly underestimated drag at elevated angles owing to inviscid assumptions. The integrated methodology demonstrates high reliability for selecting and refining airfoil geometries in UAV design, offering improved aerodynamic efficiency, extended endurance, and enhanced flight stability.