The beautiful owl is back in the news. People are fascinated by this wonderful bird’s ability to fly so silently; a silent beast gliding through the woods. Noise has become an issue to people in general, I believe, because people are more sensitive about the environment. And drones are quite noisy. They make an irritating buzzing sound. Scientists have suggested that they could learn from the wings of owls to create drones that are much quieter and the same knowledge can be applied to aircraft wings and wind turbines.
It seems that one of the keys to a quiet wing is a trailing edge which is broken. But it is more complicated than that as there are several factors involved. They are going to try designing an aerofoil with the cross section of an owl wing while focusing on the serrated trailing edge which is created by the feathers as illustrated below. They believe that they can reduce the noise of artificial wings.
When owls hunt, they are so quiet that they can’t be heard above the rustling of leaves. This must have been an evolutionary process in order to make hunting more efficient.
The serrations on the trailing edge apparently breaks up the disordered airflow and turbulent vortexes which normally form on the trailing edge of a wing. When the serrations are asymmetric as is the case with owls the noise dampening effect is even more effective.
A scientist, Liu, from Xi’an Jianotong University, China admitted that scientists are only at the beginning of developing this technique to make aerofoils quieter.
He said:
“As masters of silent flight, owls profit from a leading-edge comb, trailing-edge fringe, and down on the wing surface, as well as a unique wing cross section. How these characteristics correlate with acoustic and aerodynamic performance remains a mystery.”
He added:
“Nocturnal owls produce about 18 dB less noise than other birds at similar flight speeds due to their unique wing configuration.”
His study used computer modelling to work out that the asymmetrically-serrated wings also had a better lift-to-drag ratio. They believe that this information could help to make wind turbines more acceptable. This is important since wind turbines can be a major source of disturbance to the public.
His study is published in the journal Physics of Fluids. There is another study on the same topic on The Royal Society Publishing website entitled: Features of owl wings that promote silent flight.
Liu said that there were other things we can learn from owls in addition to making aerofoils quieter. He said that when an owl catches prey the shape of the wings are constantly changing, “so the study of the wing edge configurations during owl flight is of great significance.”
