Aeroacoustics Comparison of Owl, Hawk, and NACA0012 Airfoils Using Microphone Measurements

This study investigates the aeroacoustics performance of an owl-inspired airfoil in comparison with a conventional NACA0012 and a hawk-inspired airfoil, using experimental sound pressure measurements conducted in a semi-acoustic wind tunnel. Tests were carried out over a range of Reynolds numbers (44 × 10³ to 134 × 10³), angles of attack (0°–16°), and two chord lengths (150 mm and 250 mm), using seven microphones. The influence of flow velocity, Reynolds number, and angle of attack on sound pressure level (SPL), root-mean-square pulsating coefficient, and psychoacoustic roughness was thoroughly examined. Results show that the owl airfoil consistently demonstrates lower SPL and roughness values across a wide range of operating conditions, especially at low frequencies (50–315 Hz), which are commonly associated with laminar separation bubble shedding and trailing-edge noise. The owl airfoil’s acoustic advantage becomes particularly evident under high angles of attack and increased Reynolds numbers, where flow separation is more pronounced in the hawk airfoil. At the lowest Reynolds number, the owl airfoil exhibits predominantly laminar flow over the upper surface. With increasing Reynolds number, the boundary layer thickens and undergoes transition to turbulence, which enhances momentum exchange and delays flow separation. In contrast, the hawk airfoil experiences earlier and more pronounced separation as the angle of attack and Reynolds number increase. These findings highlight the superior noise reduction potential of bio-inspired owl airfoil in low-speed aerodynamic applications.