Owl Wings May Be Key To Quieting Wind Turbines, Aircraft
Marie Donlon | July 05, 2017
Image credit: Tony Hisgett / CC BY 2.0Hoping to one day reduce the noise given off by wind turbines and aircraft, researchers from Japan and China, inspired by the silent flight of the owl, set out to mimic the design of the owls’ wings.
Publishing their results in the journal Bioinspiration and Biomimetics, researchers examined the serrations in the edge of owls’ wings.
"Owls are known for silent flight, owing to their unique wing features, which are normally characterized by leading-edge serrations, trailing-edge fringes and velvet-like surfaces,” said lead author Professor Hao Liu, from Chiba University, Japan.
"We wanted to understand how these features affect aerodynamic force production and noise reduction, and whether they could be applied elsewhere."
Analyzing owl-inspired feather wing models with and without leading edge serrations, researchers determined that the leading edge serrations were critical to aerodynamic force and sound production.
According to Liu, "These owl-inspired leading edge serrations, if applied to wind turbine blades, aircraft wings or drone rotors, could provide a useful biomimetic design for flow control and noise reduction."
"At a time when issues of noise are one of the main barriers to the building of wind turbines, for example, a method for reducing the noise they generate is most welcome."
Excellent research. It would be fascinating to know whether the multiple vortex shedding effect noted has other useful attributes as well as noise reduction. I can imagine water and ice shedding, as well as low speed efficiency gain - or is there a trade off between leading edge complexity and mechanical efficiency? I have noticed striations in turbine leading edges after some years of use, maybe caused by parasitic oscillations of vortex nodes. Designing with the ability to shed these may have other unexpected benefits.
Hurry to study the flight of the birds, in a short time the wings of the turbines will have all cut into slices!!
Recent wind turbines are NOT physically optimized for energy extraction from common winds. Their large span and few blades configuration is optimal only for propulsion where the maximum forward thrust work is greatest vs the torsional energy put into its shaft. It is historically clear through the 20th century that essentially all functioning wind turbines (preceding the modern wind frenzy) were of many blades of limited diameter. The reason lies in the "solidus" of the "turbine" wheel. Windmills used four blades (actually like sails as would be found on ships). The practical farm turbine for pumping water and limited electricity were all like that. To get maximum energy out of a wind stream, as may blades as possible should be used. This will reduce the pressure pulse amplitude for each blade passage past an interference such as a pylon or a strut. Broadband noise results directly from turbulence at and near the physical blades. This is quelled or minimized by damping material within that turbulence generating hard surface. Hence owl wings and body feathers. All is not well, because the wind speed rises rapidly with height. A modicum of power production has been obtained so far with large diameters since the top swing reaches into the higher speed air laminum. It will be necessary to increase the tower height, making up for the reduced blade radius. Which makes thse power units all the more ugly and unsafe for aviation......... GO SOLAR!