Active control of the flow behind a backward facing step by a periodic perturbation

In this paper the active control of the turbulent separated and reattaching flow over a backward facing step is studied numerically by the Large Eddy Simulation (LES) method. The objective of the control consists to modify the separation phenomenon of the fluid in the edge of the step by application a periodic perturbation. The perturbation is realized by zero-net alternative suction and blowing of the fluid in the step edge into a separated shear layer. The found results showed the reduction of the reattachment length and enhancement of the shedding vortical frequency by the applied periodic perturbation. Also, the existence of an optimum frequency, Stp = 0.25, in term of promotion of reattachment and the increase of shedding vortical frequency. At this perturbation frequency an important modification of the dynamic of the flow is observed. The modifications observed at the optimum frequency are noticeable as the perturbation amplitude increases.