Drag reduction control based on active wall deformation

Direct numerical simulation was performed to turbulent channel flow with active wall deformation under opposition control. It is shown that when the maximum wall displacement is limited within 5 wall units, the pressure drag is negligible and the friction drag can be reduced by 7.6%. Under the control, the turbulence intensity and Reynolds shear stress are suppressed obviously, and the logarithmic region in mean velocity profile is moved upward. Influenced by the vertical motion of the wall, streaky structures are weakened in strength and enlarged in scale. The streamwise vortices moved further away from the wall with weakened strength, and their tilting and twisting angles are both reduced. The wall appears in the shape of streamwise elongated streaky structures with the mean spacing of 90 wall units.