Roaring wind turbines and thundering planes could be made much quieter and efficient if they mimic owls’ flight, say researchers from the Cambridge University.
"Many owls can hunt by stealth, swooping down and capturing their prey undetected. While we have known this for centuries, what has not been known is how or why owls are able to fly in silence," said lead researcher professor Nigel Peake.
Peake and his collaborators at Virginia Tech, Lehigh and Florida Atlantic Universities used high resolution microscopy to examine owl feathers in fine detail.
The investigation has enabled researchers to develop a prototype coating for wind turbine blades that could significantly reduce the amount of noise they make.
The method can be replicated in other types of fan blades, such as those in planes.
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, a porous and elastic fringe on the trailing edge.
"Much of the noise caused by a wing – whether it is 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 not hear them coming."
Using a similar design, the researchers 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.
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 next step is to test the coating on a functioning wind turbine.
The results are scheduled to be presented at the American Institute of Aeronautics and Astronautics (AIAA) Aeroacoustics Conference in Dallas.