The owl. A silent deadly nocturnal killer swooping down on its prey. A wind turbine. What on earth could link them? Let us tell you; a material which mimics the sound-deadening wing structure of owls has been designed to reduce noise in wind turbines. It can also be used on more modest applications such as computer fans, but also larger projects such as helicopters and planes. At first blush it seems a bizarre idea, and you might conjure up in your mind wind turbines that look like prehistoric giants birds covered in thick feathers- but surely that would increase drag and reduce aerodynamic efficiency?
Researchers from Cambridge University have developed a prototype coating for wind turbine blades, based on the feathers of an owl’s wing, that could reduce the amount of noise they make without any noticeable effect on aerodynamics. First tests indicate that the new material could actually improve speeds, producing more energy while making less noise.
Over to Professor Nigel Peake of Cambridge Uni's Department of Cambridge's Department of Applied Mathematics and Theoretical Physics:
“Many owls – primarily large owls like barn owls or great grey owls – can hunt by stealth, swooping down and capturing their prey undetected. While we’ve known this for centuries, what hasn’t been known is how or why owls are able to fly in silence.”
Owl feathers were scrutinised in granular high-res microscopic detail by the Uni (in collaboration with researchers at three institutions in the US). They found 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. It's also exclusive to owls. Prof Peake said:
“No other bird has this sort of intricate wing structure. 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 emulate/replicate the structure, the researchers looked to design a covering that would disperse, ‘scatter’, the sound generated by a turbine blade in the same way. The main objections to onshore wind turbines are appearance and the sound they make. While owl feather type developments won't make objections to wind farms on the grounds of their appearance and effect on views go away, they will address the sound issues.
They began by using a material similar to that used for brides' wedding veils to cover the blade. This did lower the surface noise, but the researchers went further and ended up designing their own prototype material- made of 3D-printed plastic. Did it work?
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 a full 10dB, according to the researchers. Next up will be to teat the material on an existing functioning wind turbine next. Since wind turbines close to communities are heavily braked in order to minimise noise, the addition of this new surface would mean that they could be run at much higher speeds – producing more energy while making less noise. For an average-sized wind farm, this could mean several additional megawatts worth of electricity.
So, watch this space. Ssshhh- It seems that we can still learn things from "wise old owl"!
The research was funded by the US National Science Foundation and the US Office of Naval Research.
. Source material gathered from various sites including Cambridge University, New Scientist and Popular Science
.Images from University of Cambridge, and Wikipedia.