University of Cambridge researchers have devised a new material that mimics the wing structure of owls which could help make wind turbines, computer fans and even planes much quieter. Early wind tunnel tests of the coating have shown a substantial reduction in noise without any noticeable effect on aerodynamics.

Owl, by Mirko Zammarchi via Creative Commons. Click image for the largest view.

Owl, by Mirko Zammarchi via Creative Commons. Click image for the largest view.

Because wind turbines are heavily braked in order to minimize noise, the addition of this new surface would mean that they could be run at much higher speeds producing more energy while making less noise. For an average-sized wind farm, this should mean several additional megawatts worth of electricity.

An investigation into how owls fly and hunt in silence has enabled researchers to develop a prototype coating for wind turbine blades that could significantly reduce the amount of noise they make.

The surface has been developed by researchers at the University of Cambridge, in collaboration with researchers at three institutions in the U.S. Their results were presented Monday June 22 at the American Institute of Aeronautics and Astronautics (AIAA) Aeroacoustics Conference in Dallas.

Professor Nigel Peake of Cambridge’s Department of Applied Mathematics and Theoretical Physics, who led the research said, “Many owls – primarily large owls like barn owls or great gray owls – can hunt by stealth, swooping down and capturing their prey undetected. While we’ve known this for centuries, what hasn’t been known is how or why owls are able to fly in silence.”

Peake and his collaborators at Virginia Tech, Lehigh and Florida Atlantic Universities used high resolution microscopy to examine owl feathers in fine detail. They observed that the flight feathers on an owl’s wing have a downy covering, which resembles a forest canopy when viewed from above. In addition to this fluffy canopy, owl wings also have a flexible comb of evenly-spaced bristles along their leading edge, and a porous and elastic fringe on the trailing edge.

Close-up view of a flight feather of a Great Grey Owl. Image Credit: J. Jaworski.  Click image for the largest view.

Close-up view of a flight feather of a Great Grey Owl. Image Credit: J. Jaworski. Click image for the largest view.

“No other bird has this sort of intricate wing structure,” said Peake. “Much of the noise caused by a wing – whether it’s attached to a bird, a plane or a fan – originates at the trailing edge where the air passing over the wing surface is turbulent. The structure of an owl’s wing serves to reduce noise by smoothing the passage of air as it passes over the wing — scattering the sound so their prey can’t hear them coming.”

In order to replicate the structure, the researchers looked to design a covering that would ‘scatter’ the sound generated by a turbine blade in the same way. Early experiments included covering a blade with material similar to that used for wedding veils, which despite its open structure, reduced the roughness of the underlying surface, lowering surface noise by as much as 30dB.

Although the ‘wedding veil’ worked remarkably well, it wouldn’t suitable to apply to a wind turbine or airplane. Using a similar design, the researchers then developed a prototype material made of 3D-printed plastic and tested it on a full-sized segment of a wind turbine blade. In wind tunnel tests, the treatment reduced the noise generated by a wind turbine blade by 10dB, without any appreciable impact on aerodynamics.

While the coating still needs to be optimized, and incorporating it onto an airplane would be far more complicated than a wind turbine, it could be used on a range of different types of wings and blades. The next step is to test the coating on a functioning wind turbine.

According to the researchers, a significant reduction in the noise generated by a wind turbine could allow them to be spun faster without any additional noise, which for an average-sized wind farm, could mean several additional megawatts worth of electricity.

There are a lot of wind turbines up worldwide. So saving on the wasteful speed brakes would not only add energy to the output, one would expect a savings in maintenance and other costs. What might make a huge difference is a coating that can be retrofitted.

Lots of potential here. Lets hope the wind turbine industry helps this along.


6 Comments so far

  1. voxelman on June 25, 2015 12:51 PM

    I’d really like to see this optimized for small (40mm-80mm) computer fans.

  2. Matt Musson on June 26, 2015 7:37 AM

    Mimmicking Bird wings will allow windmills to run silently – killing many more birds than they do now!

    Unintended cosequences.

  3. Jagdish on June 29, 2015 3:58 AM

    The windmill technology is all wrong as it is motivated by desire to replace other electricity power generation devices. For using wind energy, we should
    1. Use a funnel with bird screen to further concentrate/speed up the wind.
    2. Use a small turbine in enclosed space to further compress the air to a usable pressure.
    3. Clad the tower to get storage space for compressed air.
    Compressed air is a good low-cot energy source.

  4. dmm on June 29, 2015 9:32 AM

    @voxelman: Since the computer fan blades are just molded plastic, they could give them any surface pattern desired. But I wonder if this research applies to such high RPMs.

    @Musson: My thoughts exactly. But let’s not forget that the death toll includes many bats (very helpful insectivores, and also prey for hawks).

  5. jp straley on June 29, 2015 6:35 PM

    Birds get dirty. They preen and take baths.

    Windmill blades will get dirty, too. Goop will live in these tiny rough surfaces. Dead bugs will supply nutrients for goopy biomass.

    Nature is messy.

  6. Edward on July 2, 2015 4:45 PM

    Very interesting. Like all great inventions they are more often than not discoveries stumbling on the patterns of the great inventor our creator God Jesus.

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