低雷诺数下三维后向台阶流的流动与传热特性研究

Study on Flow and Heat Transfer Characteristics in the Laminar Flow Over A Backward-Facing Step

为研究低雷诺数下后向台阶的流动与传热特性,建立三维稳态后向台阶的数值模型。采用Fluent设定控制方程和边界条件,模拟出三维后向台阶的流场和温度场。结果表明:当雷诺数Re一定时,台阶底面中心处的Nu由初始值快速到达峰值,再从峰值迅速减小,随着距离台阶越远,Nu值不断减小并趋于平缓;由于受到侧壁的影响,二维底面和三维底面中心处的努赛尔数峰值的差值会随着雷诺数的增加而增大。同时,三维模拟底面中心上的再附着长度会随着雷诺数的增加大于二维模拟的结果;三维台阶底面的再附着点的连线呈抛物线状,顶面的会出现对称的漩涡,侧壁的流动很不规则,三维台阶中心面处的流动具有二维特性;三维台阶底面的努赛尔数的最大值不是出现在中心线处,而是分布在两个侧壁的附近。

A three-dimensional steady numerical model of backward-facing step flow is established to study flow and heat transfer characteristics of backward-facing step at low Reynolds number. The governing equations and appropriate boundary conditions are solved to obtain the flow and thermai fields by using Fluent. The results show that when Reynolds number is constant, Nnsselt number along the centerline reaches the peak Nusselt number from the initial value. With the increase of the distance downstream of the step, Nusselt number decreases rapidly and tends to be constant. Due to the effect of the side wall, the difference value of bottom peak Nusselt number between 2D-simulation and 3D-simulation is increased. In this Reynolds number range, the reattachment length of three-dimensional simulation is longer than that of two-dimensional simulation. The line connecting the reattachment points in the bottom wall is parabolic. The roof of the backward-facing step appears symmetrical vortices. Also, the streamlines of the side wall is irregu, lar. In addition, the flow downstream of the symmetrical surface remains two dimensional characteristics. According to the Nusselt number contours on the bottom wall, the maximum Nusselt number did not appear on the symmetrical surface but near the two side walls.