Control of a channel-flow behind a backward-facing step by suction/blowing

Results of the experimental investigation on control of narrow channel flow behind a backward-facing step by blowing/suction near the step foot are presented. The slots differ in both the orifice shape (rectangle or serrated) and area (50–375 · 10−6 m2) of its cross-section. The intensity of flow control is characterized by the suction/blowing flow coefficient (mass flow through the slot over mass flow above the step, suction: negative values) that varies from −0.035 up to 0.035 at Reynolds number 5 · 104 (defined on the basis of the hydraulic diameter and volume velocity). Preliminary results indicate that both blowing and suction are able to reduce the length of the separation zone down to one third of its value without control. Control effectiveness is given by absolute value of the flow coefficient. The other parameters (slot area and shape) are important only for blowing, in this case small cross-section with serrated edge is the most effective. The existing three-dimensional vortex structures near the step (resulting from interaction of boundary layers near the step edge) are influenced by suction more then by blowing. The experiments are still in progress.