In this study, opposition control with upstream sensors is applied to the turbulent channel flow at Reτ =395. As a control input, the amplitude of the actuation at the wall is proportional to the transverse velocity at an upstream sensing location in the opposite direction and varies over time. We perform direct numerical simulations of turbulent channel flow and evaluate the control performance of skin friction reduction based on the locations of upstream sensor. It is shown that the opposition control with upstream sensors exhibits a better control performance than that with a sensor directly above the actuator. The use of upstream sensors for the opposition control effectively decreases the strength of streamwise vortices and velocity fluctuations near the wall, resulting in the maximum skin friction reduction of 26% for the turbulent channel flow with the optimal upstream sensor location.
