Owl wing design may limit noise of planes, wind turbines

Noise pollution is more than annoying. Research has shown its impact on fish, songbirds and the health of humans too. But nature itself may offer a solution, with scientists in China reporting that designs based on how owl wings work may have the potential to reduce aircraft noise.

It’s not just aircraft, either. The same principle might work for drones and other unmanned air vehicles, as well as wind turbines.

“Nocturnal owls produce about 18 decibels less noise than other birds at similar flight speeds due to their unique wing configuration,” says author Xiaomin Liu of Xi’an Jiaotong University. “Moreover, when the owl catches prey, the shape of the wings is also constantly changing, so the study of the wing edge configuration during owl flight is of great significance.”

The findings, published Tuesday in the journal Physics of Fluids, are based on models the scientists used to evaluate what’s known as trailing-edge noise. It is caused when air flows across the back side of an airfoil. This causes turbulence in the air on the upper and lower surfaces of the blade or other “wing” structure.

This is the dominant sound that people hear from airplane engines. It’s also what many cities want to reduce; the authors note that Heathrow Airport in London, for example, issues fines to aircraft carriers when its strict nighttime noise rules are violated.

It’s long been tricky to find a successful solution. There’s been some improvement when serrations are used in rotating machinery, but it’s not consistent from one site or system to the next.

“The blade design of rotating turbomachinery has gradually matured, but the noise reduction technology is still at a bottleneck,” says Liu. “The noise reduction capabilities of conventional sawtooth structures are limited, and some new nonsmooth trailing-edge structures need to be proposed and developed.”

There’s still more work to be done, but the noise calculations and analysis done on the designs based on owl wings are showing promise. One finding, for example, is that an asymmetrical design reduces the noise more than the symmetrical ones do.

Still, machines like wind turbines operate in complicated airflow dynamics. How the noise reduction techniques perform in a range of different air flows isn’t yet known.

On the other hand, the owl in flight operates as a somewhat complicated “machine” too. Owls maneuver in silent low-speed glides while maintaining stability, all of which is based on factors that include complex air flows and aerodynamic principles.

“The silent flight of owls relies on the coupling effect of multiple factors,” the authors write. “These multiple factors deserve specific attention, rather than the duplication of a single coupling element, to further design quiet rotating machinery and micro-air vehicles.”