层流下不同扩张比对后向台阶流动和传热特性的影响（英文）

The Effects of Expansion Ratios in Laminar on Flow and Heat Transfer Characteristics in Backward-Facing Steps

建立三维数值模型以研究低雷诺数范围内(50≤Re≤250)不同扩张比对后向台阶流动和传热特性的影响.在宽高比恒为16的条件下,改变扩张比分别为1.5,2.0,3.0,通过Fluent计算得到流场和温度场等.结果表明:扩张比为2.0时的数值模拟结果与先前的实验结果吻合的很好.三维后向台阶底面再附着点的分布呈抛物线状分布.当雷诺数Re=200时,随着扩张比的增大,三维后向台阶上壁面两个对称旋涡的尺寸逐渐增大,底面中心线上的Nu峰值逐渐增大,并且再附着点的位置更接近于台阶.与二维数值模拟相比,在同一扩张比下,三维后向台阶底面中心线上的Nu峰值小于二维后向台阶底面Nu的峰值.

A three-dimensional steady numerical model was established to study the effects of expansion ratio on flow and heat transfer characteristics over a backward-facing step at low Reynolds number range(50≤Re≤250).Expansion ratio(ER)treated in the present study was 1.5,2.0,and 3.0 under a step aspect ratio of 16.0.The flow and thermal fields of the backward-facing step flow are simulated by use of Fluent.The present numerical results for ER=2.0 are in a good agreement with the previous experimental ones.It is found that the line connecting the reattachment points on the bottom is parabolic.When Reynolds number is constant,the scale of two symmetric vortices on the up wall of the backward-facing step becomes larger with the increase of the expansion ratio.In addition,as the increase of ER,the peak Nu on the center line of bottom is increasing and the position of the reattachment point is closer to the step.Compared with two-dimensional simulation,the peak Nu on the center line of the three-dimensional bottom is lower than that on the two-dimensional bottom at the same expansion ratio.