The most common type of noise produced by aeronautical and turbine engines, such as those encountered in planes, drones, and wind turbines, is trailing-edge noise.

For some metropolitan areas, reducing noise pollution is an important environmental goal.

In a new study, a team of researchers from Xi’an Jiaotong University exploited the features of owl wings to improve airfoil design and dramatically minimize trailing-edge noise.

“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. “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.”

When airflow passes around the back of an airfoil, trailing-edge noise is produced. The flow creates a turbulent layer of air over the upper and lower surfaces of the airfoil, which scatters and radiates noise when it flows back through the trailing edge.

Serrated trailing edges have been found to successfully minimize the noise of rotating machinery in previous investigations. The noise reduction was not universal, however, and it was highly dependent on the eventual use.

“At present, the blade design of rotating turbomachinery has gradually matured, but the noise reduction technology is still at a bottleneck,” adds 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 researchers conducted a series of rigorous theoretical simulations of simplified airfoils with features similar to owl wings using noise calculation and analysis software. They used their findings to reduce the noise produced by rotating machinery.

The noise was reduced by improving the flow conditions near the trailing edge and refining the form of the edge. Surprisingly, asymmetric serrations decreased noise better than symmetric serrations.

The scientists stressed that airfoil designs should be further assessed based on the individual application because noise reduction varied with different operating circumstances.

Wind turbines, for example, have complicated incoming flow settings that necessitate a more comprehensive noise reduction method. Examining noise reduction strategies under the effect of various input flows might broaden the scope of their conclusions.

The researchers believe their findings will be useful in airfoil design and noise reduction.

Source: 10.1063/5.0076272

Image Credit: WANG AND LIU

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