Microblowing Technique Demonstrated to Reduce Skin Friction

One of the most challenging areas of research in aerodynamics is the reduction of skin friction, especially for turbulent flow. Reduced skin friction means less drag. For aircraft, less drag can lead to less fuel burned or to a greater flight range for a fixed amount of fuel. Many techniques and methods have been tried; however, none of them has significantly reduced skin friction in the flight environment. An innovative skin-friction reduction technique, the Microblowing Technique (MBT), was invented in 1993. This is a unique concept in which an extremely small amount of air is blown vertically at a surface through very small holes. It can be used for aircraft or marine vehicles, such as submarines (where water is blown through the holes instead of air). As shown in the figure, the outer layer, which controls vertical flow, is a plate with high-vertical holes. The inner layer, which produces evenly distributed flow, is a low-permeability porous plate. Microblowing reduces the surface roughness and changes the flow velocity profile on the surface, thereby reducing skin friction.