How the silence of owls in flight could lead to low-noise aircraft

By getting up close and personal with the intricate mechanics of bird flight, scientists continue to unlock secrets that can aid in their pursuit of advanced aerodynamics, and that may include aircraft that generate a lot less noise. Scientists in Europe have developed a new type of aerofoil they say could lead to important gains in this area, by simulating the microstructures on owl feathers that allow the birds to hunt their prey in silence.

Aerospace engineers have used studies of birds in flight to further research into improved aerodynamics, the development of shapeshifting wings, how mid-air collisions might be better avoided, and even how drones could recover from them. In fact, just last month we looked at research into how barn owls are able to withstand powerful winds, which could one day lead to small-scale aircraft that can do the same.

The latest advance on this front comes from researchers at the City, University of London and Germany’s RWTH Aachen University, and reveals the role of microstructures on the leading edge of owl feathers called finlets. The scientists began by gathering 3D geometry data on typical owl feathers via high-res micro-CT scans, which enabled them to build a digital model that could be studied through computational fluid dynamics.

The serrated edge of an owl feather

The serrated edge of an owl feather

This revealed that these finlets serve to redirect the flow of air so that it behaves in a more coherent way. The team built an enlarged aerofoil inspired by finlets and put it to the test in a water tunnel, which again showed that they can redirect and stabilize the flows running across them.

The results ran counter to what the team was expecting, which was that the curvature of the finlets would actually produce miniature vortices. Instead, they found they act as thin guides that work together to smooth out the flow across the span of the wings, allowing the owls to move through the air in silence.

The team plans to build on this rudimentary model with a technical version of the aerofoil, which it will use to study the acoustics of flight further in wind tunnel testing. Ultimately, the aim is to work these types of microstructures into the design of advanced aircraft wings, potentially cutting down on the noise they generate.

The research was published in the journal Bioinspiration & Biomimetics.

Source: City, University of London

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