Bioinspired Trailing-Edge Noise Control

Strategies for trailing-edge noise control have been inspired by the downy canopy that covers the surface of exposed flight feathers of many owl species. Previous wind-tunnel measurements demonstrate that canopies of similar characteristics can reduce pressure fluctuations on the underlying surface by as much as 30 dB and significantly attenuate roughness noise generated by that surface. In the present work, surface treatments are designed to replicate the effects of the canopy in a form suitable for application to an airfoil. These treatments are installed directly upstream of the trailing edge to modify the boundary-layer turbulence before acoustic scattering by the edge. Over 20 variants of these designs have been tested by performing aeroacoustic wind-tunnel measurements on a tripped DU96-W180 airfoil at chord Reynolds numbers of up to 3 million. Compared with the unmodified airfoil, the treatments provided up to 10 dB of broadband attenuation of trailing-edge noise. The effectiveness of the treatment is not highly dependent on a particular geometry, but there appears to be strong potential for optimization. The surface treatments remain effective over an angle-of-attack range that extends over 9 deg from zero lift. Aerodynamic impact of the treatment appears minimal.