Scientists from City, University of London and Germany’s RWTH Aachen University have revealed how micro-structured finlets on owl feathers enable silent flight.
According to team lead and City professor Christoph Bruecker, this discovery could help the aerospace industry to reduce aircraft noise in future. He and his team have presented their findings in a paper titled ‘Flow turning effect and laminar control by the 3D curvature of leading edge serrations from owl wing’.
Their research outlines their translation of the detailed 3D geometry data of typical owl feather examples provided by RWTH Professor Hermann Wagner into a biomimetic aerofoil to study the aerodynamic effect on the special filaments at the leading edge of the feathers.
According to the scientists, these structures work as arrays of finlets which coherently turn the flow direction near the aerodynamic wall and keep the flow for longer and with greater stability, avoiding turbulence.
The City team was particularly inspired by the complex 3D geometry of the extensions along the front of the owl’s feathers.
After being transferred into a digital shape model, the flow simulations around those structures clearly indicated the aerodynamic function of these extensions as finlets.
According to the scientists, this effect is known to stabilize the flow over a swept wing aerofoil – typical for owls while flapping their wings and gliding.
Using flow studies in a water tunnel, Bruecker, also proved the flow-turning hypothesis in experiments with an enlarged finlet model.
Results show that the finlets act as thin guide vanes due to their special 3D curvature. The regular array of such finlets over the wing span therefore turns the flow direction near the wall in a smooth and coherent manner.
Bruecker and his team are now planning to use a technical realization of such a swept wing aerofoil pattern in an echo-free (anechoic) wind-tunnel for further acoustic tests.
They opine that the outcome of this research is integral for future laminar wing design. It also has the potential to reduce aircraft noise.
Image and content: City-University of London
