Chuck Bednar for redOrbit.com – @BednarChuck
Drawing inspiration by the way that owls can fly and hunt in silence, experts from Cambridge University in the UK, along with colleagues from the US, have come up with a prototype coating they claim can significantly reduce the noise produced by wind turbine blades.
Based on the results of early tests involving the material, which will be presented Monday at the American Institute of Aeronautics and Astronautics (AIAA) Aeroacoustics Conference in Dallas, Texas, it could make wind turbines and other types of fans blades quieter, removing the need for brakes to minimize noise production. This would make it possible for turbines to operate at much higher speeds, allowing wind farms to produce more energy without noise pollution.
“It’s been known for a long time that owls fly much more silently than would be expected, and it’s also been known for a while that their feathers have an unusual structure,” lead investigator Professor Nigel Peake from the Cambridge Department of Applied Mathematics and Theoretical Physics, explained to redOrbit via email.
“The possibility of a connection was first suggested by a very well-known acoustics engineer called Professor Geoff Lilley from Southampton UK,” he added. “But our key step forward was the realization that the feather structures were acting like a canopy to shield the wing from the turbulent flow – the interaction of the turbulence with the wing produces a lot of noise. Our coating is designed to mimic this shielding effect.”
No significant adverse affect on aerodynamics
Peake, along with colleagues from Virginia Tech, Lehigh, and Florida Atlantic Universities, used high resolution microscopy to examine owl feathers in fine detail. They discovered that the flight feathers found on an owl’s wing have a downy covering which resembles the canopy of a forest when viewed from above.
Furthermore, they also found that owl wings possess a unique, flexible comb of evenly-spaced bristles along their leading edge, and a porous and elastic fringe on the trailing edge. Peake said that no other type of bird has a wing structure quite this intricate, and that the structure reduces noise by smoothing the passage of air as it passes over the wing and scattering the sound.
The researchers set out to replicate this structure by designing a coating capable of scattering the sound generated by turbine blades. They originally used a material similar to a wedding veil, and while that worked well, it was not suitable to be applied to turbines or planes. Next, they tried a prototype material made from 3D-printed plastic, then tested it on a full-sized segment of a wind turbine blade.
Wind tunnel tests determined that the coating could reduce the noise levels generated by a wind turbine blade by 10 decibels, with no significant impact on its aerodynamic performance. While the substance could be used to treat a wide variety of different airplane wings and blades as well as wind turbines, there is still work to do before this becomes a reality.
“We’re doing more experiments to optimize the height and spacing of the fins, and also their orientation, to see what happens if the flow is not aligned perfectly with the wing chord,” Peake told redOrbit. “The really good news is that the device does not seem to adversely affect the aerodynamics too much – if it had produced a lot of extra drag for instance then it might not be very useful in practice.”
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