Owls inspire ultra-quiet aircraft and wind turbines Thursday, 24 August 2017

Researchers at the Iowa State University are taking inspiration from the wings of owls for the development of ultra-quiet aircraft and wind turbines.

According to Anupam Sharma, an Iowa State assistant professor of aerospace engineering and Walter W. Wilson Faculty Fellow, the owl is almost completely silent in flight, and this silence applies not only to gliding flight but also flapping flight.

According to Sharma, the owl’s silent flight can be credited to three factors.

First, at the leading edge of the wing there are small, fine, comb-like structures. Second, all the feathers at the trailing edge of the wing end in a pliable and porous fringe. And third, there’s a downy coat on the flight feathers.

To learn exactly how those features manipulate air flow, turbulence and pressure to produce silent flight, Sharma is scanning owl wing specimens, creating digital models and running multi-day simulations on them. He and his colleagues hope their studies will produce practical ideas for making ultraquiet aircraft and wind turbines.

While there have been previous studies of owl wings and silent flight, few have taken a high-powered computational approach to the studies.

“We can get into details that there is no way you can study with experiments,” Sharma said.

According to Sharma, the downy coat of owl wings inspired his collaborators at Virginia Tech to design model airfoils with a regular series of small, thin “finlets” and canopies near the trailing edge of the blade and running parallel to the airflow.

The research teams compared the performance of the owl-inspired airfoils to a standard, flat-surfaced airfoil.

Sharma said the computer simulations showed the owl-inspired airfoils substantially reduced the unsteady pressure on the back end of the blade surface. They found that the sound radiated by the owl-inspired design was reduced by up to 5 decibels over a wide frequency range. This enhancement was achieved without sacrificing aerodynamic performance.

Overall, the researchers confirmed the findings from the simulations, finding that the owl-inspired designs reduced noise and also that fence spacing on the airfoil is an important design parameter.

Despite the findings, it does not mean next-generation aircraft or wind turbines will look like owl wings.

“Our approach is bio-inspired as opposed to bio-mimicry,” Sharma said.

“We’re taking simplified geometries inspired by the owl wings and applying those to aircraft wings, rotor blades of jet engines and wind turbines.”

The researchers are also using 3D printing to quickly develop models to test various ideas and geometries, and applications might start at smaller scales and low speeds, such as drones or unmanned aerial vehicles.Isaac

[Image: Iowa State researchers (L-R) Bharat Agrawal, Andrew Bodling and Anupam Sharma are studying how owl wings can inspire ultra-quiet aircraft and wind turbines. Photo: Christopher Gannon.]