The double backward-facing step: effect of forcing on interacting separated flow regions

This paper demonstrates experimentally that imposed periodic forcing can significantly alter the global flow characteristics of over a double backward-facing step. The geometry consists two equal height steps spaced up to eight step heights apart. A zero-mass flux jet located at first step's top corner was issued frequencies ranging from below step-mode instability frequency approximately five times shear-layer frequency. Reattachment onto achieved for separations as low three single-step with forcing; shorter than occurred without forcing. significant reduction in mean base pressure on step, and increase second frequencies. Even large separations, effect persisted sufficiently far downstream appreciably influence development recirculation zone. Importantly, previous forced single unforced flows provide reference cases examine discuss similarities differences. study offers insight into possibilities potential outcomes control applications drag ground vehicles such pickup trucks, enhanced mixing industrial processes.