Numerical investigation of thickness variation on owl-like airfoil aerodynamics and aeroacoustics at low Reynolds number

Optimizing bio-inspired airfoils for low-Reynolds-number applications is crucial for improving aerodynamic efficiency while minimizing noise emissions in micro air vehicles, unmanned aerial vehicles, and wind turbine rotor blades. Achieving a balance between lift performance, structural integrity, and aeroacoustic benefits remains a key challenge. While previous studies have explored bio-inspired airfoil modifications, the impact of increasing thickness-to-chord (t/c) ratio on both aerodynamic and aeroacoustic performance remains underexplored, particularly in addressing laminar separation bubble effects on this passive noise reduction. This study investigates the influence of increased t/c ratio on an owl-inspired airfoil, assessing its effects on lift generation, stall characteristics, and aeroacoustic performance. Computational fluid dynamics and Ffowcs Williams-Hawkings acoustic modeling are used to analyze the modified owl airfoil (OA-T) across Reynolds numbers ranging from 2.3 × 104 to 1 × 105. Results show that the thickened variant (OA-T) offers improved lift performance at moderate-to-high angles of attack, with up to a 4 dB reduction in broadband noise and a 6 dB reduction in tonal sound pressure level at low Reynolds numbers. However, at higher Reynolds numbers, the acoustic advantage diminishes or reverses slightly, with minor tonal increases observed. These findings highlight that increasing thickness can be an effective passive noise reduction strategy in low-speed regimes, while still preserving aerodynamic functionality, making it relevant for sustainable, low-noise airfoil design applications in aviation and energy applications.