While wind turbines have been faulted for being dangerous to birds, it’s actually one of these animals -- the owl -- that’s inspired a research team to devise a new method to reduce the noise turbines make.
Researchers from Lehigh University, Virginia Tech, Florida Atlantic University, and University of Cambridge have collaborated on research, which observed the way many owl species can fly silently to invent a passive noise reduction device. The device can disrupt the air flow of turbines to cut back on the sound they make, and also has applications for other turbine-based technology used in airplanes, naval ships, and automobiles.
Justin W. Jaworski, assistant professor of mechanical engineering and mechanics at Lehigh, who worked on the research, explained to Design News in an interview what about owl flight inspired the design of the mechanism.
This image shows the feathers of the Eurasian eagle owl, (a,b) great gray owl, (c) and snowy owl (d). The ability for many owl species to fly without noise to better capture prey has inspired a cross-university research team to develop a passive noise reduction device to help cut back on noise from wind turbines. The research also has applications for airplanes, naval ships, and automobiles. (Source: Ian A. Clark, Conor A. Daly, William Devenport, W .Nathan Alexander, Nigel Peake, Justin W. Jaworski, Stewart Glegg )
“Owls are able to suppress the noise due to turbulent air flowing over their wings over the same frequency range where human ears are most sensitive, so the implications for engineering design are obvious for designs at the bird scale,” he said. “The noise produced at the trailing edge of a wing sets its minimum noise level, so to be effectively silent the owl must modify its trailing edge in a novel way. Many real-world applications (e.g. wind turbines) cite trailing-edge noise as a dominant or predominant noise source; therefore, understanding the owl trailing edge may have direct implications for industrial design for quieter operation.”
Specifically, the downy layer found on top of owl features posed particular interest for researchers, Jaworski said. The layer, which has a velvety texture, has a forest-like structure that pushes off the noisy air flow from the wing surface. When this layer is placed upstream of the trailing edge, it modifies the air flow before generating noise at the edge, he said.
Using this as a model, the team developed a 3D-printed, plastic passive noise reduction device called “finlets” based upon the structure of the fluffy down material found on owl feathers, Jaworski said. This device is comprised of small rails or fins that are aligned with the air flow upstream of the trailing edge, which disrupts the air flow in such a way to weaken noise generation at the trailing edge.
“The finlet device is passive and could be a design retrofit -- such as winglets on the tips of