The unique wing features of owls that make their flight silent could hold the key to making aircraft and wind turbines quieter, suggests new research. A team of researchers from Japan and China studied the serrations in the leading edge of owls' wings, gaining new insight into how they work to make the birds' flight silent. The results, published in the journal Bioinspiration and Biomimetics, pointed towards potential mechanisms for noise suppression in wind turbines, aircraft, multi-rotor drones and other machines.
"Owls are known for silent flight, owing to their unique wing features, which are normally characterised by leading-edge serrations, trailing-edge fringes and velvet-like surfaces," said lead author Hao Liu, Professor at Chiba University in Japan. "We wanted to understand how these features affect aerodynamic force production and noise reduction, and whether they could be applied elsewhere," Liu added.
The researchers analysed owl-inspired feather wing models with and without leading edge serrations, by combining large-eddy simulations -- a mathematical model for turbulence used in computational fluid dynamics to simulate air flows -- and Particle-Image Velocimetry, or PIV (an optical method of flow visualisation used in education and research), and force measurements in a low-speed wind tunnel.
They discovered leading-edge serrations can passively control the transition between laminar, or streamline air flow, and turbulent air flow over the upper wing surface, at angles of attack (AoA) between zero and 20 degrees. This means they play a crucial role in aerodynamic force and sound production. "These owl-inspired leading edge serrations, if applied to wind turbine blades, aircraft wings or drone rotors, could provide a useful biomimetic design for flow control and noise reduction," Liu said.