Abstract

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 × 10^3–1.2 × 10⁴. 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° to 4°, and confuser contraction ranged from 0° to 7.5°. 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.

摘要

介绍了在具有后向台阶的矩形扁平通道中纵向正负压力梯度对流动分离、附着和松弛区域中的湍流传热影响的实验研究结果。这些研究是在雷诺数为 4 × 10 ^3–1.2  × 10 ⁴的湍流状态下进行的. 台阶高度等于分离前通道高度的一半，因此其膨胀度为1.5。扩散器开口角度从 0° 到 4° 不等，混淆器收缩范围从 0° 到 7.5°。作为实验研究的一部分，测量了通道突然膨胀后流动的再循环和松弛区域的压力场和传热系数。结果表明，随着纵向压力梯度的变化，台阶后分离流的行为发生了显着变化。已经确定，对于压力梯度增加的收敛通道，努塞尔数的最大值增加，而对于扩展通道，它减小。