Owls are known for their near-silent flight, which allows them to swoop down on prey unheard. Wind turbines, on the other hand, are often accused of being too noisy. A team of British and American scientists is currently addressing the one situation with the other, by copying the structure of owl feathers to make turbine blades more quiet.
The researchers – from Lehigh University, Virginia Tech, Florida Atlantic University and the University of Cambridge – started by analyzing the wing feathers of large owls. More specifically, they were interested in the layer of down that covers the upper surface of the wings.
A newly-designed material, which mimics the wing structure of owls, could help make wind turbines, computer fans and even planes much quieter.
Early wind tunnel tests of the coating have shown a substantial reduction in noise without any noticeable effect on aerodynamics.
An investigation into how owls fly and hunt in silence has enabled researchers to develop a prototype coating for wind turbine blades that could significantly reduce the amount of noise they make.
Early tests of the material, which mimics the intricate structure of an owl’s wing, have demonstrated that it could significantly reduce the amount of noise produced by wind turbines and other types of fan blades, such as those in computers or planes. Since wind turbines 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.
The surface has been developed by researchers at the University of Cambridge, in collaboration with researchers at three institutions in the USA.
Collaborators at Virginia Tech, Lehigh and Florida Atlantic Universities used high resolution microscopy to examine owl feathers in fine detail. They observed that the flight feathers on an owl’s wing have a downy covering, which resembles a forest canopy when viewed from above. In addition to this fluffy canopy, owl wings also have a flexible comb of evenly-spaced bristles along their leading edge, and a porous and elastic fringe on the trailing edge.
In order to replicate the structure, the researchers looked to design a covering that would â€˜scatter’ the sound generated by a turbine blade in the same way. Early experiments included covering a blade with material similar to that used for wedding veils, which despite its open structure, reduced the roughness of the underlying surface, lowering surface noise by as much as 30dB.
While the â€˜wedding veil’ worked remarkably well, it is not suitable to apply to a wind turbine or aeroplane. Using a similar design, the researchers then developed a prototype material made of 3D-printed plastic and tested it 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, without any appreciable impact on aerodynamics.
According to the researchers, a significant reduction in the noise generated by a wind turbine could allow them to be spun faster without any additional noise, which for an average-sized wind farm, could mean several additional megawatts worth of electricity.