Engineers are exploring the owl species which are known for their noiseless wings allowing them to be unnoticed by their prey. They plan to use their findings in designing a “silent owl technology” which may be used in 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.
The researchers aim to know whether the owl’s noiseless wings is based upon a single attribute or the interaction of various attributes.
In other bird species, the sound of their wings can be heard whenever they fly because of the hard trailing edge. The researchers found that that it is built differently on owls as the trailing edge are porous and compliant causing significant reductions on aerodynamic noise.
"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 in a statement.
The noiseless wings are linked on the soft edge below the wings but rough surface on top. They compared the wings to a “soft carpet.” They will need further studies but researchers believe that the material explains how the owls can fly silently.
"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.
Ian Clark of Virginia Tech took photos of the owl wings to reveal its geometry. Researchers plan to copy its structure and have it incorporated on aircrafts, wind turbines, and submarines.
"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," said Jaworski.
The study was presented at the American Physical Society's (APS) Division of Fluid Dynamics meeting Sunday in Pittsburgh, Pa.
