Owl wing design reduces aircraft, wind turbine noise pollution
Serrated edge of owl wings makes them quieter than other birds, can help inform airfoil designs

Date:
January 18, 2022
Source:
American Institute of Physics
Summary:
Researchers used the characteristics of owl wings to inform
airfoil design and significantly reduce trailing-edge noise. The
team used noise calculation and analysis software to conduct a
series of detailed theoretical studies of simplified airfoils
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 optimizing the
shape of the edge suppressed the noise.



FULL STORY ========================================================================== 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.


========================================================================== InPhysics of Fluids, by AIP Publishing, researchers from Xi'an Jiaotong University used the characteristics of owl wings to inform airfoil design
and 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 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 airfoil. The flow forms a turbulent layer of air along the upper and
lower surfaces of the airfoil, 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 nonsmooth 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 airfoils
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 optimizing
the shape of the edge suppressed the noise. Interestingly, asymmetric serrations reduced the noise more than their symmetric counterparts.

Noise reduction varied with different operating conditions, so the
scientists emphasized that the airfoil designs should be further evaluated based on the specific application.

For example, wind turbines 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.

The researchers believe their work will serve as an important guide for
airfoil design and noise control.

========================================================================== Story Source: Materials provided by American_Institute_of_Physics. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Lei Wang, Xiaomin Liu. Aeroacoustic investigation of asymmetric
oblique
trailing-edge serrations enlighted by owl wings. Physics of Fluids,
2022; 34 (1): 015113 DOI: 10.1063/5.0076272 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/01/220118111351.htm

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