The stealthy, near-silent flight of owls has long fascinated scientists, who have spent hours trying to figure out how exactly such large birds are able to sail so quietly through the night sky.
Now, experts in applied mathematics, theoretical physics, and engineering have harnessed this knowledge to develop a material that reduces the noise of man-made wings—including the huge blades of wind turbines and, eventually, airplanes.
Nigel Peake, a professor at Cambridge University, said that people have long observed the quiet flight of owls without knowing exactly how it works. So, with researchers at Virginia Tech, Lehigh, and Florida Atlantic Universities, he used high resolution microscopes to examine owl feathers in detail. They found three features they believe help the birds fly so silently.
The first is “a downy covering, which resembles a forest canopy when viewed from above,” according to a description of the research. The wings also have a comb of flexible, evenly-spaced bristles on their leading edge, and a porous, elastic fringe on their trailing edge. “No other bird has this sort of intricate wing structure,” Peake said.
Much of a wing’s noise results from turbulence in the air as it passes over the trailing edge. The down, bristles, and fringe of an owl help smooth the passage of air as it passes over the wing, “scattering the sound so their prey can’t hear them coming,” Peake added.
The researches experimented with different materials, including one similar in texture to a bridal veil. Eventually, they turned to a 3D-printed plastic that they tested on turbine blades in wind tunnels.
In the tests, the blade’s noise was reduced by 10 decibels without changing its aerodynamic capabilities. Once its fully developed, the coating could make turbines quieter, reducing noise pollution, and also more efficient because it would remove the need for the brakes that are currently applied to make them quieter by slowing them down.
The next step is to test the material on a functioning turbine, the researchers said. Then, work can begin on optimizing the technology for the higher speeds and harsher conditions of aircraft.