Owl’s flight is almost inaudible, and their wings are designed in such a way that they generate a lot of lift with very little flapping. Now, scientists from Chiba University in Japan and Shanghai Jiao Tong University in China have revealed how inspiration from owls’ wings could help make quieter wind turbines, aircraft, and drones.
“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,” says Professor Hao Liu, the lead author of the study.”We wanted to understand how these features affect aerodynamic force production and noise reduction, and whether they could be applied elsewhere.”
For the study, researchers created owl-inspired feather wing models with and without leading edge serrations, by using large-eddy simulations – a mathematical model for turbulence used in computational fluid dynamics to simulate air flows – and Particle-Image Velocimetry (PIV) and force measurements in a low-speed wind tunnel. They found that the leading-edge serrations passively control the transition between laminar, or streamline air flow, and turbulent airflow over the upper wing surface, at angles of attack (AoA) between zero and 20 degrees. In other words, these serrations play a crucial role in managing aerodynamic force and sound production.
There is a trade-off between force production and sound suppression however. At lower AoAs than 15 degrees, researchers found that serrated leading-edges reduce aerodynamic performance compared to clean leading-edges. But once the AoAs goes above 15 degrees, which owl wings often reach in flight – both noise reduction and aerodynamic performance can be achieved.
“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 explains. “At a time when issues of noise are one of the main barriers to the building of wind turbines, for example, a method for reducing the noise they generate is most welcome.”
The study has been published in the journal Bioinspiration & Biomimetics.