用 Euler 方程计算某些特殊的二维分离流动

Computing Some Special Two Dimensional Separation Flows with Euler Equations

采用非定常Ｅｕｌｅｒ方程、总体时间步长、隐式时间推进，计算了几种特殊类型钝体的二维有分离绕流。一类是光滑的圆柱体，在跨音速时计算出因激波诱导分离而周期性地脱落在尾迹上的非对称涡排。另一类是带尖角的物体，如三角形柱体，计算出从尖角处脱落在尾迹上的分离旋涡，形成卡门涡街。对这两类物体，计算的平均阻力系数，分离涡脱落的Ｓｔｒｏｕｈａｌ数以及流态都与实验接近。结果表明，对于这类绕流问题，用非定常Ｅｕｌｅｒ方程计算，具有一定工程实用意义。

Separation flows passing two sorts of blunt bodies are investigated numerically by unsteady Euler equations and the implicit finite difference scheme. The first sort is the transonic flow passing a circular cylinder. The computation reveals the flow separation induced by the shock wave and the separation vortices shedding downstream periodically. The other one is cylinder with sharp corner, such as that with triangular or semi circular cross section. The separation vortices shedding as a form of Karman vortex street from the sharp corner are also revealed. For these sorts of the bodies, the present computation gives the average drag coefficients, the Strouhal number is related to the shedding frequency of the separation vortices, and the flow pattern. They are all in good agreement with the experiments.