Owlsare exceptional predators. In addition to their impressive vision and hearingcapabilities, they are also able to fly almost silently. This stealthy flight is thanks to the structureof their wings, which researchers have analyzed and mimicked todevelop a prototype coating that they claim could significantly reduce the noisegenerated by wind turbines, computer fans and airplanes.
Usingfine detail microscopy, the researchers from the University of Cambridge in the US and VirginiaTech, Lehigh University and Florida Atlantic University in the US examined owl feathersin fine detail, revealing a downy covering that they say resembles a forestcanopy when viewed from above. They also saw a flexible comb of evenly-spacedbristles along the wing's leading edge, while the trailing edge shad a porousand elastic fringe.
"No other bird has this sort ofintricate wing structure," said Professor Nigel Peake of Cambridge’sDepartment 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, aplane or a fan – originates at the trailing edge where the air passing over thewing surface is turbulent. The structure of an owl’s wing serves to reducenoise by smoothing the passage of air as it passes over the wing – scatteringthe sound so their prey can’t hear them coming."
Early attempts to replicate thisstructure included covering a blade with a wedding veil-like material, which, despitethe open structure of the material, reduced the roughness of the underlyingsurface and cut the surface noise by up to 30 dB.
Realizing that applying a weddingveil to a turbine or airplane isn't feasible, the team 3D printed a prototypemade of plastic and tested it on a full-sized segment of a wind turbine blade.Subjecting the blade to wind tunnel tests, the researchers saw a reduction innoise of 10 dB. Importantly, they reported no appreciable impact onaerodynamics.
The team is now planning to test thecoating on a functioning wind turbine, and say that it could allow suchturbines to spin faster and generate more electricity than they do currently.This is because wind turbines are currently braked to minimize noise, andletting them spin faster could mean several extra megawatts worth ofelectricity for an average sized wind farm.
In addition to quieter wind turbines,the researchers say the coating could also find applications on a range ofdifferent types of wings and blades – however, the coating still needs to beoptimized and incorporating it into airplane wings would be far morecomplicated than a wind turbine blade.
The team will present the results oftheir study ay the American Institute of Aeronautics and Astronautics (AIAA)Aeroacoustics Conference in Dallas today.
Source: University of Cambridge
