The Secrets of Owls’ Nearly Noiseless Wings

Many owl species have developed specialized plumage to effectively eliminate the aerodynamic noise from their wings – allowing them to hunt and capture their prey in silence. A research group working to solve the mystery of exactly how owls achieve this acoustic stealth presented its findings: "Vortex Noise Reductions from a Flexible Fiber Model of Owl Down," at 8:39 a.m. on Sunday, November 24, 2013 at the American Physical Society's (APS) Division of Fluid Dynamics meeting, held November 24 – 26, in Pittsburgh, Pennsylvnia-- work that may one day help bring "silent owl technology" to the design of aircraft, wind turbines, and submarines. "Owls possess no fewer than three distinct physical attributes that are thought to contribute to their silent flight capability: a comb of stiff feathers along the leading edge of the wing; a flexible fringe a the trailing edge of the wing; and a soft, downy material distributed on the top of the wing," explained Dr. Justin Jaworski, assistant professor in Lehigh University's Department of Mechanical Engineering and Mechanics. His group is exploring whether owl stealth is based upon a single attribute or the interaction of a combination of attributes. For conventional wings, the sound from the hard trailing edge typically dominates the acoustic signature. But prior theoretical work carried out by Dr. Jaworski and Dr. Nigel Peake at the University of Cambridge revealed that the porous, compliant character of the owl wing's trailing edge results in significant aerodynamic noise reductions. "We also predicted that the dominant edge-noise source could be effectively eliminated with properly tuned porous or elastic edge properties, which implies that that the noise signature from the wing can then be dictated by otherwise minor noise mechanisms such as the 'roughness' of the wing surface," said Dr. Jaworski.
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