HEAT-TRANSFER CONTROL BY USING JET DISCHARGE IN REATTACHMENT REGION DOWNSTREAM OF A BACKWARD-FACING STEP

The effect of an air jet perpendicular to the main flow across a backw ard-facing step on the local heat transfer and pressure coefficients w as investigated. The relative height of the step and the position and velocity of the jet were varied, with the aim of controlling the heat transfer characteristics. The exit of the jet was set into the wall op posite the step, and created a bubble of circulating air downstream. T he reattachment region of the main flow shifted upstream when the jet was moved upstream or its velocity increased in the case of jet locate d downstream of step, enhancing the heat transfer. When the jet was lo cated nearly opposite the step, a bistable flow pattern was observed, characterized by different sizes of circulating bubble which created d ifferent heat transfer and pressure distributions.