November 25, 2013
Stealth Properties Of Owl Wings Could Lead To Quieter Aircraft, Wind Turbines
[ Watch the Video: Aerodynamic Inspiration From Silent Owl Wings ]
redOrbit Staff & Wire Reports - Your Universe Online
Several different owl species have developed specialized plumage to essentially eliminate aerodynamic noise from their wings, according to Justin Jaworski, assistant professor in Lehigh University's Department of Mechanical Engineering and Mechanics. Jaworski and his colleagues are attempting to figure out exactly how the birds accomplish this feat and adapt it to technological design.
“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,” said Jaworski, whose team is analyzing whether or not the trait is the result of a lone attribute or the interaction of several different features.
With most types of bird wings, the sound created by the hard trailing edge typically makes up the bulk of the acoustic signature. However, Jaworski and University of Cambridge applied mathematics professor Nigel Peake previously discovered that the porous, compliant character of owl wings significantly reduces the aerodynamic noise produced during flight.
“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,” Jaworski said.
The top of an owl’s wing contains a velvety down which creates a surface similar to that of a soft carpet, and while this material has not received much in-depth analysis when it comes to the unique noise-reducing attributes of owls, the study authors believe it could eliminate sound at the source through an unusual sound absorbing mechanism.
“Our current work predicts the sound resulting from air passing over the downy material, which is idealized as a collection of individual flexible fibers, and how the aerodynamic noise level varies with fiber composition,” Jaworski explained.
“If the noise-reduction mechanism of the owl down can be established, there may be far-reaching implications to the design of novel sound-absorbing liners, the use of flexible roughness to affect trailing-edge noise and vibrations for aircraft and wind turbines, and the mitigation of underwater noise from naval vessels,” he added.
Image 2 (below): The three unique wing features believed to make owls fly silently are shown in this graphic. Credit: J. W. Jaworski, I. Clark