One of the most commonly heard complaints about wind turbines is that they're loud. Wind farms are usually built a far enough distance away from communities that the noise is negligible, but a new biomimetic technology inspired by the stealthy flight of owls could lead to wind turbines, planes and even computer fans that are virtually silent.
This is significant because not only would quieter turbines make communities more open to having them nearby, but because wind turbines are currently heavily braked in order to keep noise to a minimum, having a way to make them operate quietly could mean that the bladed could run at much higher speeds and produce more energy. In fact, average-sized wind farms could add several megawatts to their capacity.
Researchers at the University of Cambridge, have come up with a prototype coating for wind turbine blades that could make them a lot quieter and they owe the advancement to one of nature's greatest hunters, the owl. Owls don't only have great eyesight and sharp talons, they also employ some pretty amazing engineering in their wings that allows them to fly and dive for prey in silence.
"No other bird has this sort of intricate wing structure," said Professor Nigel Peake of Cambridge’s Department of Applied Mathematics and Theoretical Physics, who led the research. "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. 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’t hear them coming."
Peake, along with a team from Virginia Tech, Lehigh and Florida Atlantic Universities, studied owls' flight feathers under high resolution microscopes and discovered that the wings are covered with a downy covering that resembles a forest canopy from above, a flexible comb of bristles on the leading edge, and most importantly, a porous and elastic fringe of feathers at the trailing edge that dampens sound.
The researchers then started to develop a coating that could replicate the effect of the fringe that scatters sound. They came up with a porous coating made of 3D-printed plastic. In wind tunnel tests, the coating reduced the noise generated by a wind turbine blade by 10 decibels, without affecting aerodynamics
The researchers plan to next test the coating on operational wind turbines to see if they improve the power output while keeping the noise down.