Owl wings inspire noise reduction solution for wind turbines

A material which mimics the wing structure of owls has been designed to reduce noise in wind turbines, computer fans and even planes.  

A group of researchers from Cambridge University has developed a prototype coating for wind turbine blades, based on an owl’s wing, that could reduce the amount of noise they make without any noticeable effect on aerodynamics. Early tests have indicated that the new material could also improve speeds, producing more energy while making less noise.

“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 of Cambridge’s Department of Applied Mathematics and Theoretical Physics, who led the research. “While we’ve known this for centuries, what hasn’t been known is how or why owls are able to fly in silence.”

High-resolution microscopy was used for the surface, developed in collaboration with researchers at three institutions in the US, to examine owl feathers in granular detail. The researchers observed that the flight feathers on an owl’s wing have a downy covering as well as a flexible comb of evenly-spaced bristles along their leading edge, plus a porous and elastic fringe on the trailing edge.

“No other bird has this sort of intricate wing structure,” said 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.”

To replicate the structure, the researchers looked to design a covering that would ‘scatter’ the sound generated by a turbine blade in the same way. Initially, they used a material similar to that used for wedding veils to cover the blade. While this did indeed lower the surface noise, the researchers ended up designing their own prototype material.

Made of 3D-printed plastic, the material was tested on a full-sized segment of a wind turbine blade. In wind tunnel tests, the treatment reduced the noise generated by a wind turbine blade by 10dB, according to the researchers.

However, they said it would be much harder to incorporate it onto a plane. Researchers hope to optimise the material and test it on a functioning wind turbine next, which could make a difference for an average-sized wind farm for example, as the turbine could be spun faster.

The research was funded by the US National Science Foundation and the US Office of Naval Research and is a collaboration between Cambridge University and Virginia Tech, Lehigh and Florida Atlantic. Their results will be presented on Monday at the American Institute of Aeronautics and Astronautics (AIAA) Aeroacoustics Conference in Dallas.

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