Green Car Congress reports that researchers at the University of Stuttgart have succeeded, using computer simulations, in developing a method for stabilizing active drag reduction for the airfoils of commercial airliners. They claim their approach could lead to fuel economy gains of 10-15%.
Range is limited by aerodynamic drag and even a modest reduction of the drag provides significant fuel savings. Recent advances in electronics and control technologies make active boundary layer control possible.
The surface of an aircraft wing moving through the air at high speed generates a boundary layer that increases in thickness toward the trailing edge. The layer becomes increasingly turbulent and eventually sheds eddies as the air flows along the wing. Both the layer’s thickness and the eddies generate significant drag.
If the airfoil is perforated with a very large number of tightly spaced microscopic perforations (~50 microns diameter), a vacuum can be applied to maintain a relatively thin boundary layer that doesn't develop eddies. With a uniform pattern of perforations the system is unstable, the researchers have developed a hole pattern that creates a stable boundry layer.
A 10-15% increase in fuel economy means a tremendous savings for airlines, since fuel is the largest single cost to airlines. In addition it means that CO2 emissions are reduced by a corresponding amount.
I remember reading about experimental implementations of this at least 10 years ago. The big problem is keeping the small holes open, with insects impingment at low altitudes being the biggest problem (think bugs on the windshield). The solution at the time was to pump a water/detergent mix out of the holes during takeoff and landing. Corrosion closing up the holes was also a problem.
Posted by: donb | October 20, 2006 at 09:56 AM