本文对后台阶分离流动中涡结构的演变进行了大涡模拟,研究了流场结构的变化规律。详细讨论了随着雷诺数的增加流场结构的典型特征的变化规律,指出流场中的涡结构随着雷诺数的增大变得十分复杂和丰富,回流区的数目、大小及其出现的位置也显著地不同。这些结果与已有的一些实验值和流场显示结果是吻合的。在此基础上,进一步研究了高雷诺数时流场中大尺度涡结构的瞬时发展和演化过程,展示了其中大涡的产生、追随、吸引、合并和破碎等过程。对于高雷诺数情况,对大涡模拟得到的数值结果进行了统计,得到的时均速度分布以及台阶后方的回流区长度与现有的其他实验结果符合得很好。本研究是针对后台阶分离流动深入开展湍流控制以及两相流动研究的基础。 ; In this paper, the evolution of eddy structures in the backward-facing step flow was studied by using large eddy simulation. The typical flow behavior was discussed in detail. It is shown that the vortex structures become more abundant and complex with increasing of Reynolds number of the flow. The number, the length and the position of the re-circulation region vary significantly with Reynolds number, which agree well with the experiment results both in quantitative and qualitative. Based on these researches , the large eddy coherent structures evolving in spatially and temporally under the turbulent flow with high Reynolds number were visualized. The mean velocity and the reattachment length of mean flow fields were also obtained by statistic method, which agreed well with the experiment data. The present research paves a way for the further study of turbulence control and the two-phase turbulent flow. ; Department of Applied Physics