Owl-inspired wind turbine blades could reduce noise pollution
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Researchers studying the properties of silent owls’ wings have found that their leading-edge serrations are vital in sound suppression and could provide inspiration for silent wind turbine blades and other machinery.
When debating the merits and drawbacks of wind power as an alternative to fossil fuels, the issue of noise pollution is mentioned frequently; a turbine 300m from a home will be heard at up to 43 decibels. Adjusting the standard design of turbine blades to make them near-silent could make wind turbines far more appealing, particularly to local people affected by the noise.
In order to explore the possible approaches to developing quiet wind turbines, Japanese and Chinese researchers collaborated on a study into the serrations in the leading edges of owls’ wings. This has shed light on how silent movement through air could be achieved in artificial objects.
The flight of owls is famously silent; some types of owls, such as barn owls, can swoop just inches from their prey without detection.
“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 Professor Hao Liu of Chiba University, Japan, the study’s lead author.
“We wanted to understand how these features affect aerodynamic force production and noise reduction and whether they could be applied elsewhere.”
The researchers used a low-speed wind tunnel to study owl-inspired feather wing models. They employed analytic tools including mathematical models for turbulence to simulate different air flows, force measurements, and optical methods for air flow visualisation.
The researchers analysed wing models with and without the leading edge serrations characteristic of owls’ wings, and found that these leading-edge serrations can control the transition between different types of air flow, playing a vital role in aerodynamic force and sound production.
“We found, however, that a trade-off exists between force production and sound suppression. Serrated leading-edge reduces aerodynamic performance at Angles of Attack (AoAs) lower than 15° compared to clean leading-edges, but can achieve noise reduction and aerodynamic performance at AoAs above 15°, which owl wings often reach in flight said Professor Liu.
Taking inspiration from owls’ wings, potential biomimetic mechanisms could be designed to suppress noise in wind-turbines, multi-rotor drones and even aircraft, the researchers conclude in their Bioinspiration and Biomimetics report.
“This owl-inspired 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,” said Professor Liu.
“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.”