Direct numerical simulation of turbulent flow over a backward-facing step
Direct numerical simulation of turbulent flow over a backward-facing step
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DOI：
10.1017/s0022112096003941
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发表时间：
1997-01-10
影响因子：
3.7
通讯作者：
Kim, J
中科院分区：
文献类型：
--
作者：
Le, H;Moin, P;Kim, J
本文采用直接数值求解Navier-Stokes方程的方法研究了后台阶的湍流流动。在雷诺数为5100（基于台阶高度h和入口自由流速度）和膨胀比为1.20的条件下进行模拟。展向平均压力波动等值线和再附着长度的时间行为表明，自由剪切层的Strouhal数为0.06的近似周期性行为的证据。瞬时速度场表明，再附着位置沿展向变化，并在平均值6.28h左右振荡。统计结果与Jovic & Driver（1994）的实验数据非常吻合。对后向台阶流有两个以前没有报道过的观测结果：（a）在所考虑的相对低雷诺数下，在回流区看到大的负表面摩擦;峰值\C-f\大约是高雷诺数下实验测得值的2.5倍;（B）恢复区的速度分布低于通用对数律。速度分布偏离对数律表明，在分离后20个台阶高度处，湍流边界层没有完全恢复。回流区的湍动能收支与湍流混合层的湍动能收支相似。湍流输运项对收支有重要贡献，耗散峰值约为产生峰值的60%。在剪切层中速度-压力梯度相关和粘性扩散可以忽略不计，但在近壁区两者都很重要。这种趋势在整个再循环和再附着区域都可以看到。在恢复区，预算表明，自由剪切层的影响仍然存在。
Turbulent flow over a backward-facing step is studied by direct numerical solution of the Navier-Stokes equations. The simulation was conducted at a Reynolds number of 5100 based on the step height h and inlet free-stream velocity, and an expansion ratio of 1.20. Temporal behaviour of spanwise-averaged pressure fluctuation contours and reattachment length show evidence of an approximate periodic behaviour of the free shear layer with a Strouhal number of 0.06. The instantaneous velocity fields indicate that the reattachment location Varies in the spanwise direction, and oscillates about a mean value of 6.28h. Statistical results show excellent agreement with experimental data by Jovic & Driver (1994). Of interest are two observations not previously reported for the backward-facing step flow: (a) at the relatively low Reynolds number considered, large negative skin friction is seen in the recirculation region; the peak \C-f\ is about 2.5 times the value measured in experiments at high Reynolds numbers; (b) the velocity profiles in the recovery region fall below the universal log-law. The deviation of the velocity profile from the log-law indicates that the turbulent boundary layer is not fully recovered at 20 step heights behind the separation.The budgets of al Reynolds stress components have been computed. The turbulent kinetic energy budget in the recirculation region is similar to that of a turbulent mixing layer. The turbulent transport term makes a significant contribution to the budget and the peak dissipation is about 60% of the peak production. The velocity-pressure gradient correlation and viscous diffusion are negligible in the shear layer, but both are significant in the near-wall region. This trend is seen throughout the recirculation and reattachment region. In the recovery region, the budgets show that effects of the free shear layer are still present.