Owls are known for their near-silent flight, which allows them to swoop down on prey unheard. Wind turbines, on the other hand, are often accused of being too noisy. A team of British and American scientists is currently addressing the one situation with the other, by copying the structure of owl feathers to make turbine blades more quiet.
The researchers – from Lehigh University, Virginia Tech, Florida Atlantic University and the University of Cambridge – started by analyzing the wing feathers of large owls. More specifically, they were interested in the layer of down that covers the upper surface of the wings.
That down is made up of a forest of tiny hairs, which each stick up almost perpendicular to the main feather before bending back in the direction of the air flow. Each hair also has a barb at the end, which interlocks with barbs on surrounding hairs. The result is that the down is topped with a soft canopy of linked hair tips, which the air flows over instead of the rougher feather surface beneath.
Using a 3D printer, the scientists partially replicated that structure in the form of a series of "finlets" that could be attached to the trailing edge of wind turbine blades. Although those finlets do feature a unidirectional layer of "hairs" like the down, they don't have the interlocking barbs at their ends. According to the researchers, this makes the material even more aerodynamic than the owl down, as air is channeled straight through it instead of being deflected off of it.
In wind tunnel tests, it was found that when attached to an airfoil such as a turbine blade, the finlets could lower wind noise by as much as 10 decibels without affecting aerodynamic performance. The technology could conceivably also be applied to things like car door seals and windows, where wind noise can likewise be a problem.
This isn't the first time that we've seen wind turbine blades copying animals' body structure. Previously, the bumps on humpback whales' flippers have been replicated in order to improve the blades' performance.
Source: Lehigh University