Wind turbines could be made considerably quieter in the future after Cambridge University scientists developed a new material based on the unique downy wings that allow owls to fly silently.
Early tests demonstrate that coating the fan blades in this new material could significantly reduce the noise produced by a wide range of machines, including wind turbines, computers and even aircraft.
Although the project is still at a fairly early stage, the scientists are hopeful their invention could revolutionise the onshore wind-farm industry, in which projects frequently meet strong opposition from locals who are concerned about the noise they will produce – as well as their effect on the view.
The invention could also enable wind farms to produce more energy by allowing the blades to spin faster without generating any extra noise, the researchers said.
“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,” said Professor Nigel Peake of Cambridge University, who led the research. Professor Peake and his collaborators at Virginia Tech, Lehigh and Florida Atlantic universities in the US examined the owls’ feathers using powerful microscopes and found they were designed in such a way as to smooth and then scatter the sound produced by air turbulence.
Owl wings have a downy covering of fine hair, which resembles a forest canopy when viewed from above. The leading, or front, edge of the wing has a comb of evenly spaced bristles, while the back edge has a porous fringe, the researchers 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,” Professor Peake said. “The structure of an owl’s wing serves to reduce the noise by smoothing the passage of the air as it passes over the wing – scattering the sound so their prey can’t hear them coming,” he added.
The scientists set about replicating the wing’s structure by designing a coating that would scatter the sound generated by a turbine blade in the same way. After various tests they hit upon a method that involved a prototype material made of 3D-printed plastic and tested it on a full-sized segment of wind-turbine blade. In tunnel tests, the treatment was found to reduce substantially the noise level without any appreciable impact on aerodynamics.
The next step is to test the coating on a functioning wind turbine.
The research will be presented at the American Institute of Aeronautics and Astronautics’ aeroacoustics conference in Dallas.
It comes after the UK Government announced last week plans to limit the development of new onshore wind farms. It will drop crucial subsidies on 31 March 2016 – a year earlier than it had previously said – and change the planning rules to make it virtually impossible for wind-farm proposals to go ahead without widespread local support.
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