Study on Period Flow and Heat Transfer Characteristics for Backward-Facing Step in Transition Flow
In order to study the period flow and heat transfer characteristics for backward-facing step in transition flow, a two-dimensional incompressible numerical model of backward-facing step flow was established. The internal flow field and the Nusselt number (Nu) distributed on the bottom wall downstream of the backward-facing step were studied with the unsteady numerical method. The results show that the large scale vortexes rotate in opposite directions in the middle area downstream of the step and the small scale vortexes attach to both upper and lower walls. The vortexes attached to the lower wall influence the velocity field near the wall surface and enhance the Nusselt number on the bottom wall. The Nusselt number reaches the peak value in the turning point downstream of each bound vortex. There are multiple Nusselt number peaks on the bottom wall along the flow direction. The maximum Nusselt number appears at the reattachment point. When the Reynolds number is 700, the Nusselt number fluctuates only in the downstream of the reattachment point because there is no bound vortex in the primary recirculation region. When the Reynolds number is 1200, the Nusselt number fluctuation occurs upstream of the reattachment point because bound vortexes appear in the primary recirculation region.