US Patent 8113469 Passive micro-roughness array for drag modification

The present invention is directed to a micro-array surface that provides for either drag reduction or enhancement. In one aspect, an aerodynamic or hydrodynamic wall surface that is configured to modify a fluid boundary layer on the surface comprises at least one array of roughness elements disposed on and extending therefrom the surface. In one example, the interaction of the roughness elements with a turbulent boundary layer of the fluid reduces the skin friction drag coefficient of the surface over an identical smooth surface without the roughness elements.