中文摘要：

对DSMC方法中压力边界条件的实现给出了一种改进的方法，并分区模拟了微尺度后台阶气体流动，得到了其流动的一般典型结构．计算结果表明经典后台阶流动中的回流区在一定参数范围内仍然存在，但上壁面的分离区消失．讨论了流动参数对流动结构的影响，并给出了再附长度与流动参数的关系．

英文摘要：

A modified trcatment for pressure boundary conditions in DSMC is shown, The microscale backward-facing gas flow is computed by a partitioned domain DSMC method and a general flow construction is obtained. It is shown that the recirculating flow region attached to the backward-facing step exists in the microscale flow with proper conditions while the region of separation on upper side does not. A discussion about the effect of flow parameters is given and a relationship between reattachment length and Reynolds number is obtained.