Conservationists are concerned about the effects of the noise of wind turbines on wildlife and some people who live near turbines complain about their noise.
Researchers led by Nigel Peake at the University of Cambridge have turned to owls for ideas about how to reduce the noise. Owls are famously silent predators, able to surprise their prey thanks to their sound-damping wings.
Owls’ wings have two unique features that make them 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.
The research team added a number of fins that trail across and off the edge of the surface of an aerofoil. 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 – about 1 millimetre apart across the aerofoil.
The best-performing fins cut noise by a factor of 10 compared with finless aerofoils.
As well as making them quieter, the researchers believe that attaching fins to wind turbines might even help them to generate more energy. Currently, many wind turbines are artificially braked so that they don’t make too much noise. With the owl wing design, the turbines could run faster without getting louder.