Oct 17, 2017 | By Benedict
Researchers at Iowa State University are using 3D printing to develop propellor blades inspired by owl wings. The innovative designs could lead to quieter aircraft, wind turbines, and other machines.
Iowa State's Bharat Agrawal, Andrew Bodling, and Anupam Sharma
There are a few obvious reasons why you might not see owls very often. They're creatures of the night, for starters, which makes them both unlikely to appear during the day and hard to discern under cover of night.
But they’re also incredibly silent flyers. While the occasional “twit twoo” might give the game away, owls—despite their size—make surprisingly little noise when they fly. That means you might not even notice if one flies right over your head.
It’s this impressive quietude that has inspired Iowa State’s Anupam Sharma and his team to take a closer look at the mechanics of the nocturnal bird.
“The owl is almost completely silent in flight,” says Sharma, an assistant professor of aerospace engineering and Walter W. Wilson Faculty Fellow. “Owls are not only silent in gliding flight, but also in flapping flight.”
According to Sharma, there are three main reasons why owls fly so quietly: fine, comb-like structures on the leading edge of the wing; a pliable and porous fringe on feathers at the trailing edge of the wing; and a downy coat on the bird’s flight feathers.
For Sharma, an aeroacoustics specialist, investigating the mechanics of an animal isn’t generally part of the job. But with the impressively quiet owl, the assistant professor needed to get a closer look.
Sharma has done this by 3D scanning various owl wing specimens, turning them into digital 3D models that he can run through simulation software. This has allowed him to figure out how those three wing features affect air flow, turbulence, and pressure to produce a virtually silent motion.
These simulations are highly advanced too. Sharma is using supercomputing facilities at Argonne National Laboratory in Lemont, Illinois, where more than 16,000 processors are being used to propel virtual owls.
Using these simulations, the assistant professor has discovered some important things—not just in terms of bird anatomy, but also things that can inform real-world mechanical engineering.
For one, the simulations show that airfoils based on owl wings can substantially reduce the unsteady pressure on the back end of a blade surface. Owl-like designs can also reduce sound by up to 5 decibels without having an effect on aerodynamic performance.
3D printed turbine blades inspired by owl wings
But how do you replicate the soft and ultimately organic nature of wings and feathers for things like turbine blades, traditionally made of hard metals?
Sharma and colleagues have a few ideas.
By 3D printing airfoils with a serrated leading edge—designed to replicate the fine comb-like structures on the owl’s wing—the Iowa State researchers found that noise was reduced significantly when compared with airfoils with a flat leading edge, also reducing the unsteady pressure on the back end of the blade surface. So even though there's a big material difference, copying the subtle form of the owl wing has produced a comparable effect.
The researchers also tried 3D printing small, thin finlets and canopies near the blade trailing edge.
To validate their experiments, the Iowa State researchers invited researchers from Virginia Tech to test the new designs using their own simulation software. Excitingly, the Virginia Tech team confirmed that the owl-inspired designs decreased noise without compromising performance.
This, Sharma says, could have a big impact on the design of things like wind turbines and aircraft, which could reduce their noise emissions by implementing these owl-inspired features.
“The results of this research could have an impact on the design of silent air vehicles with application in national defense, commerce, and transportation,” Sharma says.
Others seem to agree: the National Science Foundation is supporting Sharma’s studies with a five-year, $500,000 CAREER grant, while the Iowa Space Grant Consortium has contributed a $100,000 grant.
But no amount of money, sadly, will result in aircraft that look like owls.
“Our approach is bio-inspired as opposed to bio-mimicry,” Sharma clarifies. “Our designs won’t look like owl wings.
“We’re studying the physical mechanisms behind the owl’s silent flight. Then we’re taking simplified geometries inspired by the owl wings and applying those to aircraft wings, rotor blades of jet engines, and wind turbines.”
Sharma plans to continue using 3D printing to quickly iterate new designs.
Posted in 3D Printing Application
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Those look like drone propellers! One of the biggest drawbacks of flying drones (especially around other people) is the loud noise they make. Could these designs be used to make quieter drones??
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