If birds could be ninjas, owls would make the best ones. Silent and agile, the winged creatures leave their prey with no time to escape as they swoop in for the kill. This stealth ability has inspired scientists to create quieter movement for airfoil designs across everyday technologies, including aircraft, vehicles, drones, and wind turbines.
Researchers from Xi’an Jiaotong University in Xi’an, China specifically used owl wings as the inspiration for quieter turbomachinery blades, which can be noisy as air sweeps over the trailing edge of their curved surfaces. (Turbomachinery is a term that describes machines that transfer energy between a rotor and a fluid, including both turbines and compressors).
The scientists found that serrated (or sawtooth) trailing edges reduce the noise of rotating machinery, especially when shaped more like the edges of owl wings. Air that flows over these comb-like shapes breaks up instead of continuing in straight lines, which muffles the whoosh of the owl passing by. The downy feathers on the rest of the wing may also absorb sound. The researchers describe their work in a paper published in the journal Physics of Fluids late last year.
“Nocturnal owls produce about 18 decibels less noise than other birds at similar flight speeds due to their unique wing configuration,” Xiaomin Liu, one of the paper’s authors, says in a press release. “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.”
Since the earliest days of human flight, inventors have been inspired by birds. The Wright brothers, for instance, recognized that birds’ wing shapes were crucial in getting off the ground, so they copied those properties in their mechanical airplane design. Yet scientists are still befuddled when faced with the noisy problem of trailing-edge dissonance, a phenomenon in which air moves noisily over the back edge of an airfoil; it’s the last bit of an airplane wing the air touches as it whooshes over it from front to back.
“I would say that the owl has been a long-standing spirit animal, if you will, for the air acoustics community,” Justin Jaworski, a mechanical engineer at Lehigh University in Bethlehem, Pennsylvania, tells Popular Mechanics. “[W]hen you’ve exhausted a lot of innovative ideas, you look for other means of inspiration. And the owl has been a source of inspiration for at least 80 years.”
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