Fly like the wind (Image: Christopher Ousdal/Alamy)

Moving silently through the air is not just for the birds. Wind farms inspired by the stealthy flight of owls could generate more energy without annoying those who live nearby, say researchers.

Turbines create emissions-free electricity by using the wind to turn propeller-like blades around a rotor. But conservationists are concerned about the effects of their noise on terrestrial and marine life, and people who live near turbines demand quiet operation too.

Now Nigel Peake of the University of Cambridge and his colleagues have turned to owls for inspiration. Owls are famously silent predators, able to surprise their prey thanks to sound-dampening wings.

Peake looked at two features that make their wings silent. Evenly spaced bristles along the width of the wings break up sound waves as an owl flies, preventing them from building up and producing noise. At the same time, a canopy of downy feathers reduces air pressure on the wings’ surface, providing a dampening effect. “These features are absolutely unique to owls,” says Peake.

Taking flight

Next, the team made its own wings by taking an aerofoil and adding a number of fins that trail across and off the edge of the surface. The fins replicate the owl’s evenly spaced bristles, and also disrupt surface pressure on the aerofoil, reducing the sound waves it produces.

When the researchers tested the wings in a wind tunnel, they found that noise reduction worked best when the fins were close together, spaced 1 millimetre apart across the aerofoil.

The best-performing fins cut noise by a factor of 10 compared with finless aerofoils. The team will present the work at the American Institute of Aeronautics and Astronautics conference in Dallas, Texas, later this month.

As well as making them quieter, attaching fins to wind turbines might even help them to generate more energy.

“Many wind turbines are artificially braked so that they don’t make too much noise,” says Peake. With this technology, the turbines could run faster without getting louder. The fins do produce extra drag on wings, but more rapid spinning would outweigh any energy lost, says Peake. His team is now working with a turbine manufacturer to test the idea.

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