Why owls may hold the key to reducing noise from drones, planes and even house fans

By Mark Waghorn via SWNS

Owls hold the key to reducing noise from drones, airplanes, wind turbines and household fans, according to new research.

The birds of prey are nature's most efficient hunters thanks to serrated wings - that enable them to fly quietly.

They open the door to soundless aircraft wings, propellor blades or rotors.

In a warming world, fans can combat illnesses and even death. But they can keep people awake at night because of the noise.

Lead author Dr. Xiaomin Liu, of Xi'an Jiaotong University, China, said: "Nocturnal owls produce about 18 decibels less noise than other birds at similar flight speeds due to their unique wing configuration.

"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 World Health Organization says noise pollution is a serious risk to wellbeing.

It also interferes with daily activities at school, work, home and during leisure time.

It can disturb sleep, cause cardiovascular and psycho-physiological effects, reduce performance and change social behavior.

Most noise from wings - be it a bird, a plane or fan - originates at the trailing edge.

Air passing over the surface becomes suddenly turbulent. Owls have a solution to this problem.

Their feathers produce a flexible and porous fringe which smooths its passage.

They are the secret to the animal's impressive stealth - helping it pounce on voles, mice, hares, foxes - and even other birds.

Dr. Liu said: "Trailing-edge noise is the dominant source of sound from aeronautical and turbine engines like those in airplanes, drones and wind turbines.

"Suppressing this noise pollution is a major environmental goal for some urban areas."

Previous studies found serrations can dampen the noise of rotating machinery.

But reduction was not universal - depending heavily on the final application.

Dr. Liu said: "At present, the blade design of rotating turbomachinery has gradually matured, but the noise reduction technology is still at a bottleneck.

"The noise reduction capabilities of conventional sawtooth structures are limited, and some new nonsmooth trailing-edge structures need to be proposed and developed to further tap the potential of bionic noise reduction."

Computer simulations showed simplified airfoils reminiscent of owl wings suppressed the noise of rotating machinery.

Interestingly, asymmetric shapes worked better than symmetric counterparts. Noise reduction varied with different operating conditions.

People have known for centuries that owls fly silently - swooping undetected on their scurrying prey.

The amazing natural phenomenon can inspire us to develop better airfoil designs, said Dr. Liu.

It enables them to plunge steeply downwards - and then take off again. They can also hear prey - without it hearing them.

The feathers on the upper wing surface have a particularly detailed and complex micro-structure with layer upon layer of interleaved barbs and hairs.

Examining noise techniques under the influence of different incoming flows would make the conclusions more universal, said Dr. Liu.

The researchers believe the work published in the journal Physics of Fluids will serve as an important guide for airfoil design and noise control.