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Bio-inspired canopies for the reduction of roughness noise

Accepted version
Peer-reviewed

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Type

Article

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Authors

Clark, IA 
Daly, CA 
Devenport, W 
Alexander, WN 

Abstract

This work takes inspiration from the structure of the down covering the flight feathers of larger species of owls, which contributes to their ability to fly almost silently at frequencies above 1.6 kHz. Microscope photographs of the down show that it consists of hairs that form a structure similar to that of a forest. The hairs initially rise almost perpendicular to the feather surface but then bend over in the flow direction to form a canopy with an open area ratio of about 70 percent. Experiments have been performed to examine the noise radiated by a large open area ratio canopy suspended above a surface. The canopy is found to dramatically reduce pressure fluctuations on the underlying surface. While the canopy can produce its own sound, particularly at high frequencies, the reduction in surface pressure fluctuations can reduce the noise scattered from an underlying rough surface at lower frequencies. A theoretical model is developed which characterizes the mechanism of surface pressure reduction as a result of the mixing layer instability of flow over forest canopies.

Description

Keywords

roughness noise, bio-inspired, noise reduction

Journal Title

Journal of Sound and Vibration

Conference Name

Journal ISSN

0022-460X
1095-8568

Volume Title

385

Publisher

Elsevier
Sponsorship
Office of Naval Research (ONR) (N62909-12-1-7116)
Office of Naval Research (Grant IDs: N00014-13-1-0244, N00014-14-1-0242)