Friction drag reduction through damping of the near-wall spanwise velocity fluctuation

Direct numerical simulation (DNS) of a turbulent channel flow is performed in order to explore the possibility of reducing wall friction drag and saving energy through damping of the spanwise velocity fluctuation. Starting from an idealized feedback control, we extend the idea to a practically realizable control, in which only the streamwise wall shear stress is required as sensor input, while actuators of finite size are employed. This control scheme offers drag reduction of up to 20%, which is the highest value achieved by existing feedback controls based on the streamwise wall shear stress. In addition, the control power input remains two orders of magnitude smaller than the pumping power for the uncontrolled flow.