The serrated edge of owl wings makes them quieter than other birds, which may be used to assist develop airfoils.
The features of owl wings were utilized to guide airfoil design, which resulted in a considerable reduction in trailing-edge noise. The researchers conducted a series of rigorous theoretical simulations of simplified airfoils with features similar to owl wings using noise calculation and analysis tools. They used what they learned to reduce the noise of whirling machines. The noise was reduced by improving the flow conditions near the trailing edge and refining the form of the edge.
The most common kind of noise produced by aeronautical and turbine engines, such as those found in aircraft, drones, and wind turbines, is trailing-edge noise. For certain metropolitan areas, reducing noise pollution is an important environmental objective.
Researchers from Xi’an Jiaotong University exploited the features of owl wings to guide airfoil design and dramatically minimize trailing-edge noise, as published in Physics of Fluids by AIP Publishing.
“Due to their distinctive wing shape, nocturnal owls emit around 18 dB less noise than other birds at comparable flying speeds,” stated author Xiaomin Liu. “Moreover, the form of the owl’s wings changes frequently while it captures food, therefore studying the wing edge configuration during owl flight is very important.”
When airflow flows around the rear of an airfoil, trailing-edge noise is produced. The flow creates a turbulent layer of air over the top and lower surfaces of the airfoil, which scatters and radiates noise as it flows back through the trailing edge.
Serrated trailing edges have been shown to successfully minimize the noise of spinning equipment in previous investigations. The noise reduction was not universal, however, and it was highly dependent on the eventual use.
“At the moment, rotating turbomachinery blade design is steadily maturing, but noise reduction technology is still at a bottleneck,” Liu added. “Conventional sawtooth designs have limited noise reduction capabilities, thus some innovative nonsmooth trailing-edge structures must be suggested and created to fully realize the promise 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 tools. They used what they learned to reduce the noise of whirling machines.
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 more than symmetric serrations.
The scientists stressed that airfoil designs should be further assessed depending on the individual application since noise reduction varied with various operating circumstances.
Wind turbines, for example, have complicated incoming flow settings that need a more comprehensive noise reduction method. Examining noise reduction strategies under the effect of various input flows might broaden the scope of their results.
The researchers think their findings will be useful in airfoil design and noise reduction.