Analog VLSI system for active drag reduction

surface. I n today’s cost-conscious air transportation industry, fuel costs are a substantial economic concern. Drag reduction is an important way to increase fuel efficiency and reduce these costs. Even a 5% reduction in drag translates into estimated savings of millions of dollars in annual fuel costs. Organized structures that play an important role in turbulence transport may cause large skin friction drag. Commonly observed near-wall streamwise vortices cause high drag in turbulent flows (Figure 1, next page). The interaction of these vortices, which appear randomly in both space and time, with the viscous layer near a surface creates regions of high surface shear stress. This stress, when integrated over a surface, contributes to the total drag. Previous attempts to reduce drag by controlling turbulent flows focused on ways to prevent the formation or limit the strength of these vortices. However, the microscopic size of these vortices, which decreases as the Reynolds number of the flow increases, has limited physical experimentation. Further limiting analytical approaches is the inherent complexity of the nonlinear NavierStokes equations.