As they swoop down on mice at night, the prey have no idea what's coming. This is because owls are the experts of silent flight. By studying how the birds manage this stealthy feat, scientists have developed a sound-dampening technology that could be used to coat wind turbines, airplane wings, and even the fans of computers, to make them quieter.
“Many owls – primarily large owls like barn owls or great grey owls – can hunt by stealth, swooping down and capturing their prey undetected,” said Professor Nigel Peake, who led the study presented at the American Institute of Aeronautics and Astronautics Aeroacoustics Conference in Dallas. “While we’ve known this for centuries, what hasn’t been known is how or why owls are able to fly in silence.”
Researchers from the University of Cambridge in association with three institutions in the U.S. have created a prototype coating that mimics how owls are able to reduce the noise produced as air moves over their wings. By using high-resolution microscopy, the team were able to check out the bird’s feathers in fine detail and work out exactly how they manage their silent flight.
The owls have three features to help them do this. Firstly, they have a downy covering, which the researchers say looks like the canopy of a forest when looked at from above. Secondly, they have a flexible comb of bristles running along their wings' leading edges, and finally, they have a porous fringe on the trailing edges. They think that these features help to dissipate the sound as it’s produced.
Close-up view of a flight feather from a great grey owl. J. Jaworski
“No other bird has this sort of intricate wing structure,” explains Peake. “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. 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 researchers then set to replicate these sound-scattering structures, creating a 3D-printed cover that could be fitted onto a wind turbine blade. Testing this in a wind tunnel, the team found that the new coating reduced the noise generated by 10 decibels while having no negative impact on the blades' aerodynamics. The coating still needs to be reformed and developed, but these preliminary results are promising.
It is hoped that the new tech could further be used on commercial wind farms, to help reduce the level of noise they create – one of the main complaints from people who live near them. In addition to this, they hope that it could actually help to increase the amount of energy produced by the turbines, as currently they have to have brakes on them to stop them from revolving too quickly and making too much noise. With this new techn-owl-ogy, such limits wouldn’t have to be enforced.
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