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Owl wing design could cut noise from aircraft and wind turbine blades

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The shape of owl wings, which allow the animals to move quietly as they hunt prey, could inspire new aerofoil designs (Credit: Wang and Liu)
The shape of owl wings, which allow the animals to move quietly as they hunt prey, could inspire new aerofoil designs (Credit: Wang and Liu)

Researchers have replicated the characteristics of owl wings to create new aerofoil designs aimed at reducing trailing-edge noise.

The team from Xi'an Jiaotong University in China were inspired by quiet nocturnal owls in their research.

"Nocturnal owls produce about 18 decibels less noise than other birds at similar flight speeds due to their unique wing configuration," said author Xiaomin Liu. "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."

Trailing-edge noise is the dominant source of sound from aircraft and turbine engines, like those in aeroplanes and wind turbines. The noise is generated when airflow passes along the back of an aerofoil, forming a turbulent layer of air along the upper and lower surfaces. When that layer of air flows back through the trailing edge, it scatters and radiates noise.

Previous studies explored serrated trailing edges, finding that the serrations effectively reduced the noise of rotating machinery. The noise reduction was not universal however, depending heavily on the final application.

"At present, the blade design of rotating turbomachinery has gradually matured, but the noise reduction technology is still at a bottleneck," said Liu. "The noise reduction capabilities of conventional sawtooth structures are limited, and some new non-smooth trailing-edge structures need to be proposed and developed to further tap the potential of bionic noise reduction."

The team used noise calculation and analysis software to conduct a series of detailed theoretical studies of simplified aerofoils with characteristics reminiscent of owl wings. They applied their findings to suppress the noise of rotating machinery.

Improving the flow conditions around the trailing edge and optimising the shape of the edge suppressed the noise. Asymmetrical serrations were found to reduce noise more than their symmetrical counterparts.

The amount of noise reduction varied with different operating conditions, so the scientists emphasised the need for further evaluation based on specific applications. Wind turbines have complex incoming flow, for example, requiring a more general noise reduction technology.

The work, which was published in Physics of Fluids, could provide a guide for better aerofoil design and noise control, the team said.


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