On the Thermo-flow Behavior of a Wall Jet with an Oscillating Segment over a Backward-facing Step

We numerically investigate fluid–structure interaction (FSI) in a forced-convection wall-jet flow over a backward-facing step, considering various airflow and elastic-segment parameters. The flow is incompressible and laminar ( ). Downstream of the step, the jet encounters a heated bottom wall containing an oscillating elastic segment. The influence of elastic segment length, location, oscillation amplitude, and frequency on heat transfer is systematically examined. Results show that increasing the segment length enhances the area-averaged Nusselt number by enlarging the effective fluid–solid contact area. Placing the segment upstream yields greater enhancement than downstream placement by shortening the reattachment length. Higher oscillation frequencies intensify near-wall convection and further increase heat transfer. Maximum heat transfer is achieved when the oscillation amplitude equals the step height. Additionally, segment oscillation reduces the skin-friction coefficient by promoting near-wall motion. Overall, these findings demonstrate a dual benefit: heat-transfer augmentation accompanied by reduced pumping losses, which is attractive for compact heat-exchanger applications.