高速尤其是高超音速飞行是航空航天发展的主流方向.目前,70 km以上高超音速飞行器的需求越来越大.当飞行高度达到或超过70 km时,稀薄效应明显,此时连续介质假设失效,传统的连续流体运动方程(NS方程)和相应的CFD方法已经失效.利用连续流体运动方程(NS方程)和直接模拟蒙特卡洛方法(DSMC),对四个典型K n(K n分别为0.001、0.01、0.1和1)下的圆柱绕流进行了计算.分析比较发现,随着K n的增大,流场中的激波间断结构变弱变粗,甚至消失,圆柱后方的分离区也逐渐变小直到消失. High-speed, especially hypersonic flight is the mainstream of aerospace development.At present, the demand for hypersonic vehicles above 70 km is increasing.When the flight altitude reaches or exceeds 70 km, the lean effect is obvious, at this time, the continuum hypothesis fails, The traditional continuous fluid equations of motion (NS equations) and the corresponding CFD methods have been invalidated.Using the equations of continuous fluid motion (NS) and direct simulation Monte Carlo (DSMC), the four typical K n , 0.01, 0.1 and 1) were calculated.The analysis and comparison showed that as the K n increases, the discontinuous structure of the shock wave in the flow field becomes weaker, even disappears, and the separation zone behind the cylinder Gradually smaller until disappear.