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.
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.
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.
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.