Aircraft noise pollution could be dampened with design based on owl wings
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The wings of owls have inspired new designs for aircraft wings that help to drastically cut down on noise pollution.
'Trailing-edge noise' is the dominant source of sound from aeronautical and turbine engines like those in aeroplanes, drones, and wind turbines.
Researchers from Xi’an Jiaotong University in China used the characteristics of owl wings to inform aerofoil designs that help to significantly reduce the trailing-edge noise.
“Nocturnal owls produce about 18 decibels less noise than other birds at similar flight speeds due to their unique wing configuration,” said study author Xiaomin Liu.
“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.”
Trailing-edge noise is generated when airflow passes along the back of an aerofoil. The flow forms a turbulent layer of air along the upper and lower surfaces of the aerofoil, and 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 reduce the noise of rotating machinery. However, the noise reduction was not universal, 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. Asymmetric serrations were found to reduce the noise more than their symmetric counterparts.
Noise reduction varied with different operating conditions so the researchers believe that aerofoil designs should be further evaluated based on their specific application.
Wind turbines for example have complex incoming flow environments, which require a more general noise reduction technology. Examining noise reduction techniques under the influence of different incoming flows would make their conclusions more universal.
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