The Effect of Longitudinal Pressure Gradient on Heat Transfer in a Separated Flow Behind a Sudden Expansion of the Channel

The results of an experimental study of the influence of longitudinal positive and negative pressure gradients in a rectangular flat channel with a backward-facing step on turbulent heat transfer in the zones of separation, attachment, and relaxation of the flow are presented. The studies were carried out in a turbulent flow regime at Reynolds numbers 4 x 10(3-1.2) x 10(4). The height of the step was equal to the half height of the channel before separation, so that the degree of its expansion was 1.5. The angle of diffuser opening varied from 0 degrees to 4 degrees, and confuser contraction ranged from 0 degrees to 7.5 degrees. The pressure fields and heat transfer coefficients in the recirculation and relaxation regions of the flow behind a sudden expansion of the channel were measured as a part of the experimental study. It is shown that with a change in the longitudinal pressure gradient, the behavior of the separated flow behind the step changes significantly. It has been determined that for a convergent channel with an increase in the pressure gradient, the maximum value of the Nusselt number increases, while for the expanding channel it decreases. The maximum Nusselt number position shifts downstream with diffuser expansion and approaches a step in the confusion flow.