Control of Reattachment Length in a Backward-Facing Step Flow Using an Inline Plate

Flow separation and reattachment behind a backward-facing step is a classical benchmark for studying separated flows and their control. In this study, we investigate the influence of a passive control element—an inline rigid plate—on the reattachment dynamics downstream of the step. Through a series of two-dimensional numerical simulations, we demonstrate that the placement and angle of attack of the inline plate significantly affect the recirculation bubble and reattachment length. The presence of the plate alters the shear layer development and modifies the momentum exchange between the recirculation zone and the outer flow, enabling a controllable shift in the reattachment point. By systematically varying the geometric parameters of the plate, we identify configurations that either shorten or lengthen reattachment, offering a simple and effective method for flow control. These findings have potential implications for heat transfer enhancement, drag reduction, and flow stabilization in engineering systems.