The secrets of owls' near noiseless wings

Nov 24, 2013
The three unique wing features believed to make owls fly silently are shown in this graphic. Credit: J. W. Jaworski, I. Clark

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 will present their findings at the American Physical Society's (APS) Division of Fluid Dynamics meeting, held Nov. 24 – 26, in Pittsburgh, Pa.—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 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 . But prior theoretical work carried out by Jaworski and Nigel Peake at the University of Cambridge revealed that the porous, compliant character of the owl wing's trailing edge results in significant aerodynamic 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 Jaworski.

The velvety down atop an owl's wing creates a compliant but rough surface, much like a soft carpet. This down material may be the least studied of the unique owl noise attributes, but Jaworski believes it may eliminate sound at the source through a novel mechanism that is much different than those of ordinary sound absorbers.

"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 said.

The researchers' results are providing details about how a fuzzy – compliant but rough – surface can be designed to tailor its acoustic signature.

A photographic study of actual owl feathers, carried out with Ian Clark of Virginia Tech, has revealed a surprising 'forest-like' geometry of the down material, so this will be incorporated into the researchers' future theoretical and experimental work to more faithfully replicate the down structure. Preliminary experiments performed at Virginia Tech show that a simple mesh covering, which replicates the top layer of the 'forest' structure, is effective in eliminating some sound generated by rough surfaces.

"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 , and the mitigation of underwater noise from naval vessels," said Jaworski.

Explore further: Finding faster-than-light particles by weighing them

More information: The presentation "Vortex Noise Reductions from a Flexible Fiber Model of Owl Down," is at 8:39 a.m. on Sunday, November 24, 2013 in the David L. Lawrence Convention Center, Room 319. ABSTRACT: http://meeting.aps.org/Meeting/DFD13/Event/202030

Related Stories

Noise research to combat 'wind turbine syndrome'

Jun 01, 2011

(PhysOrg.com) -- University of Adelaide acoustics researchers are investigating the causes of wind turbine noise with the aim of making them quieter and solving 'wind turbine syndrome'.

Researchers develop 'anti-noise' panel for quiet aircraft

May 08, 2013

Researchers from the University of Twente's CTIT research institute have developed a prototype lightweight panel that uses anti-noise to reduce noise levels inside aircraft. The panels can be used as a replacement for the ...

If you cut down a tree in the forest, can wildlife hear it?

Dec 14, 2012

A new tool developed by the Wildlife Conservation Society (WCS) and its partners is being used by scientists and land managers to model how noise travels through landscapes and affects species and ecosystems— a major factor ...

Recommended for you

Finding faster-than-light particles by weighing them

Dec 26, 2014

In a new paper accepted by the journal Astroparticle Physics, Robert Ehrlich, a recently retired physicist from George Mason University, claims that the neutrino is very likely a tachyon or faster-than-light par ...

Controlling core switching in Pac-man disks

Dec 24, 2014

Magnetic vortices in thin films can encode information in the perpendicular magnetization pointing up or down relative to the vortex core. These binary states could be useful for non-volatile data storage ...

Atoms queue up for quantum computer networks

Dec 24, 2014

In order to develop future quantum computer networks, it is necessary to hold a known number of atoms and read them without them disappearing. To do this, researchers from the Niels Bohr Institute have developed ...

New video supports radiation dosimetry audits

Dec 23, 2014

The National Physical Laboratory (NPL), working with the National Radiotherapy Trials Quality Assurance Group, has produced a video guide to support physicists participating in radiation dosimetry audits.

Acoustic tweezers manipulate cell-to-cell contact

Dec 22, 2014

Sound waves can precisely position groups of cells for study without the danger of changing or damaging the cells, according to a team of Penn State researchers who are using surface acoustic waves to manipulate ...

User comments : 1

Adjust slider to filter visible comments by rank

Display comments: newest first

Macrocompassion
not rated yet Nov 25, 2013
As I have been claiming for years, this soft downy surface effect when applied to large aircraft wings will stabilize the boundary layers and both delay the transition of laminar flow to turbulence and also damp the degree of turbulence afyer it has occured in the flow on the rear part of the hard surface. The latter trend for covering the wing with a "sea of grass" is the first that should be examined because it is easier to design and use.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.