Control of the viscous sublayer for drag reduction

We investigate the possibility of manipulating turbulence structures in the viscous sublayer for the purpose of drag reduction using a direct numerical simulation of a turbulent channel flow. Recognizing that a great portion of production of vorticity occurs in the viscous sublayer, a body force is used to suppress spanwise velocity in the sublayer, and a significant amount of drag reduction is obtained. A more realistic body force or wall movement in the spanwise direction using instantaneous wall-shear stress in a closed-loop control is shown to reduce drag as much as 35%. Implementation of such a body force using an electromagnetic force is also discussed.