Direct numerical simulation of backward-facing step turbulent flow controlled by wave-machine-like traveling wave

A direct numerical simulation of turbulent flow over a backward-facing step is performed. To control flow separation, a wall-normal body force in the form of a wave-machine-like traveling wave is applied to the top surface of the step. In this control, the recirculation bubble is periodically released in time and in the streamwise direction. In addition, a pair of longitudinal vortices is generated above the step and in the recirculation bubble and the released separation bubble, which causes three effects that reduce the reattachment length: a decrease in the secondary bubble streamwise length, an enhancement of the negative wall-normal velocity, and an increase in Reynolds shear stress.