Nature-inspired three-dimensional surface serration topologies enable silent flight by suppressing airfoil-turbulence interaction noise

Abstract: As natural predators, owls fly with astonishing stealth due to the sophisticated serrated surface morphology of their feathers that produces advantageous flow characteristics and favorable boundary layer structures. Traditionally, these serrations are tailored for airfoil edges with simple two-dimensional patterns, limiting their effect on overall noise reduction while negotiating tradeoffs in aerodynamic performance. Here, we formulate new design strategies that can mitigate tradeoffs between noise reduction and aerodynamic performance by merging owl feather and cicada insect wing geometries to create a three-dimensional topology that features silent and efficient flight. Aeroacoustics and aerodynamics experimental results show that the application of our hybrid topology yields a reduction in overall sound pressure levels by up to 9.93% and an increase in propulsive efficiency by over 48.14% compared to benchmark designs. Computational fluid dynamics simulations reveal that the three-dimensional, owl-inspired surface serrations can enhance surface vorticity. The produced coherent vortex structures serve to suppress the source strength of dipole and quadrupole pressure sources at various Reynolds numbers, resulting in a universal noise reduction effect. Our work demonstrates how a bioinspired three-dimensional serration topology refines the turbulence-airfoil interaction mode and improves multiple functionalities of an aerodynamic surface to enable quieter and more fuel-efficient, aerial vehicles.