Comparative aeroacoustics performance of bio-inspired and conventional airfoils via coherent particle velocity method

In this study the aeroacoustics performance of owl airfoil compared to hawk and National Advisory Committee for Aeronautics (NACA) 0012 airfoils by two chord numbers of C = 150 mm and C = 250 mm, were investigated experimentally by the help of CPV (Coherent Particle Velocity) method. The effects of different parameters such as free-stream velocity, Reynolds number, angle of attack and hotwire position on the six different airfoils were examined in wind tunnel experiments. The CPV method results show that for frequencies below 2 kHz under attached flow conditions, the owl airfoil exhibited the lowest Sound Pressure Levels (SPL), aligning with self-noise cancelation hypothesis. At Re = 74 × 10 3 , the SPL reached a minimum, likely due to the elimination of laminar separation bubbles during boundary layer transition. Also, for the hawk airfoil, a distinct behavior was observed below 50 Hz, where SPL increased linearly to a peak at 50 Hz, likely due to vortex shedding, with minimal Reynolds number influence. In addition, SPL variations above 1 kHz were less sensitive to Reynolds number changes, aligning with noise from shear layer instabilities. The owl airfoil exhibited the same behavior, including the elimination of Laminar Separation Bubbles (LSB) at identical Reynolds numbers for both chord lengths. In contrast, the hawk and NACA0012 airfoils showed significant variations in vortex shedding and shear layer instabilities at the same Re.