Published: 13 April, 2009, 14:08
Edited: 13 April, 2009, 14:08
Air drag on vehicles can be reduced by outfitting them with artificial feathers, a research team believes. Real birds have been using the trick for ages.
In addition to long feathers, which birds use to take wing and keep in the air, they have smaller ones called coverts. Coverts in the back of the wing vibrate in the airflow when the bird is gliding.
An Italian team of fluid physics researchers at the University of Genoa used computer modeling to see how big an effect these feathers have on flight efficiency, reports New Scientist magazine. They used a 20-cm diameter cylinder with artificial coverts in a virtual wind tunnel.
The 4 to 6 cm long and 0.5 mm in diameter bristles covered the cylinder at a density of around three fibers per square centimeter, and orienting parallel to the wind. When the wind blew, they started to vibrate just like real coverts do, and reduced the drag on the cylinder by approximately 15%.
The effect is due to the fibers interfering with the air flowing along the surface and preventing the forming of a low-pressure zone behind the cylinder. This zone causes turbulence and increases drag. A similar process explains why fresh, fuzzy tennis balls can speed through the air faster than worn ones, says Alessandro Bottaro, head of the team.
The researchers hope artificial feathers could be used in aircraft or submarines to make them more efficient. The effect will not be as dramatic as in the virtual test, of course, since modern vehicles are already streamlined to reduce drag.