三维热化学非平衡流动非结构网格DSMC方法及其应用

Implementation of 3-D Unstructured DSMC Method for Thermodynamic and Chemical Non-Equilibrium Flow and Its Application

研究了过渡流域三维热化学非平衡流动DSMC方法实现的过程。以四面体非结构网格为基本单元，提出一种新型的高效搜索算法，该算法不仅可以快速跟踪模拟分子在网格之间的迁移，而且可以准确判别分子与物面是否相互作用，避免了原有算法中分子表面反射的非确定论判据。设计了适合三维DSMC方法的动态局部时间步长技术，节约了计算时间。将碰撞距离的思想引人到非结构网格上来，有效地消除了网格尺度小于三分之一平均自由程的限制。利用Fortran90的动态分配内存技术编制了适用于任意外形的通用计算程序。最后对全尺寸航天飞机高超声速绕流进行了数值试验，计算结果验证了该算法的可行性及高效性。

Unstructured DSMC method has been studied to calculate 3-D thermodynamic and chemical reaction non-equilibrium flow. A new automatic searching method is presented, by which the deterministic criterion for a molecule to reflect on a certain surface element is used instead of a probabilistic one. In order to improve computing efficiency and save running time, a adaptive local time stepping is designed. Collision distance is introduced to unstructured DSMC method which can avoid restriction that the cell dimension should be of the order of one third the local mean free path. Dynamic allocation feature of Fortran90 is fully exploited which makes the code more flexible. Finally, application of the 3-D unstructured DSMC method to the full shuttle geometry was made. The results of numerical experiment confirm the feasibility of method mentioned above in some extent.