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Structure of owl feathers inspires prospect of quieter aircraft

Image credit: Javier Alonso Huerta/Dreamstime

A UK study has revealed how micro-structured finlets on owl feathers enable silent flight – a discovery that could pave the way for reducing the noise of future aircraft.

The study was conducted by researchers at City, University of London, led by Professor Christoph Bruecker, and was published in the Institute of Physics journal, Bioinspiration and Biomimetics.

Their research outlines their translation of the detailed 3D geometry data of typical owl feather examples provided by Professor Hermann Wagner at RWTH Aachen University in Germany into a biomimetic aerofoil to study the aerodynamic effect on the special filaments at the leading edge of the feathers. 

The results from the study showed that these structures work as arrays of finlets that coherently turn the flow direction near the aerodynamic wall and keep the flow for longer and with greater stability, avoiding turbulence.

The City research team was inspired by the complex 3D geometry of the extensions along the front of the owl’s feathers. These were reconstructed by Professor Wagner and his team in previous studies using high-resolution micro-CT scans.

Up close image of Owl serration feather

Close-up image of serration feather from an owl.

Image credit: Professor Christoph Bruecker

After being transferred into a digital shape model, the flow simulations around those structures (using computational fluid dynamics) clearly indicated the aerodynamic function of these extensions as finlets, which turn the flow direction in a coherent way, the team said. This effect is known to stabilise the flow over a swept wing aerofoil, typical for owls while flapping their wings and gliding.

Using flow studies in a water tunnel, Professor Bruecker also proved the flow-turning hypothesis in experiments with an enlarged finlet model.

His team found that instead of producing vortices, the finlets act as thin guide vanes due to their special 3D curvature. The regular array of such finlets over the wingspan, therefore, turns the flow direction near the wall in a smooth and coherent manner.

Wingspan of an owl

Wingspan of an owl.

Image credit: Professor Hermann Wagner

The team plans to use a technical realisation of such a swept-wing aerofoil pattern in an anechoic wind-tunnel for further acoustic tests. The researcher believes the outcome of this research will prove to be important for future laminar wing design and has the potential to reduce aircraft noise.

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