For all of engineers' design wisdom, they have not been able to come up with a silent flight solution as effective as an owl's.

Inspired by owls' ability to fly at high speeds without alerting their prey with noise, engineers have been working for years to devise ways to mimic the silencing structure found on owl feathers for use on the man-made wings of wind turbines, fans, and eventually airplanes. At the American Institute of Aeronautics and Astronautics Aeroacoustics Conference, a group of researchers from the University of Cambridge presented their prototype of a 3D-printed plastic material that noticeably reduced the noise that wind turbine blades generate.

"Much of the noise caused by a wing - whether it's attached to a bird, a plane or a fan - originates at the trailing edge where the air passing over the wing surface is turbulent," Nigel Peake, a professor in Cambridge's Department of Applied Mathematics and Theoretical Physics, said in a statement. "The structure of an owl's wing serves to reduce noise by smoothing the passage of air as it passes over the wing - scattering the sound so their prey can't hear them coming."

The feathers on the front edge of an owl's wings are lined with fringes. These fringes are not for decoration, but instead serve to break up the turbulent air flowing over the wing's edge into smaller, quieter "micro-turbulences." This contributes to owls' ability to fly nearly silently, a very useful skill for a predator that hunts while in flight.

"No other bird has this sort of intricate wing structure," said Peake in a statement. 

Moving through the air quietly is a desirable quality for a variety of machines as well, including fans and airplanes. For wind turbines in particular, the noise their blades create as they whoosh through the air has been a major obstacle. So researchers are working on ways to incorporate the owl's ingenious technique into the turbines to cut down on noise.

In previous experiments, they had success in reducing noise using a material similar to that used for wedding veils, but found that this material is not suitable for use in wind turbines or airplanes. So the researchers turned to 3D printing to replicate the fine structures found on owl feathers. 

They tested 3D-printed material, made from plastic, on a full-sized wind turbine blade. The coating reduced the noise that the blade generate by 10 decibels, a difference large enough for the human ear to detect. The researchers are still working to optimize the material, however, both to enhance its noise reducing qualities and to make the technology applicable to a wide variety of wings and blades.

That birds are helping improve wind turbine technology is a bit ironic as one of the major issues facing wind turbines is that the blades can strike birds as they fly by, especially when the turbine towers are placed along migratory routes. Hopefully engineers will show their gratitude to owls for their design help by making wind turbines that are more bird-friendly as well as quieter.

Photo: Dazzie D | Flickr

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