DSMC位置元方法中的表面元的程序标识及分子表面反射确定论判据

PROGRAM MARKING OF SURFACE ELEMENTS ANDTHE DETERMINATION OF MOLECULAR SURFACEREFLECTION IN POSITION ELEMENTALGORITHM OF DSMC METHOD^1)'2)

在直接模拟Ｍｏｎｔｅ－Ｃａｒｌｏ（ＤＳＭＣ）方法的位置元方法中，精确描述物面形状、准确判断分子是否与某一表面元相撞，直接关系着气动力热的计算精度，是该方法需要解决的关键问题．为解决此问题，给出了发展的ＤＳＭＣ方法在计算三维过渡领域的位置元方案的两个改进首先，编制了一个对所有外形描述均可做到标识表面元及计算表面元面积等工作的通用程序，并通过两个例子验证了该程序的快速性和有效性；其次，发展了分子表面反射确定论判据，代替了原有的几率判据，与圆球自由分子流准确解和过渡领域贴体网格ＤＳＭＣ结果进行比较，证明了上述判据的有效性．

In the position element algorithm of DSMC, the crucial questions to be solved arethe exact description of body surface configuration and precise determination whether a moleculecomes into collision with a certain surface element. Those issues are directly related to the accuracyin calculation of aerodynamic force and heating. In order to solve these questions, two innovationsconcerning the improvement of our position element version in the calculation of three-dimensiontransitional flow by the DSMC method are given in this paper. First a general program is compiledwhich accomplishes all the work of marking the surface elements and calculating the element surfaceareas and other surface characteristics for any presentation of the body configuration, with twoexamples verifying its speediness and validity. Then, the deterministic criterion for a molecule toreflect on a certain surface element, instead of a probabilistic one, is developed. The validity ofabove-mentioned criterion is checked by comparison with the accurate solution of free molecule flowaround a sphere and the results of DSMC calculation by using the body fitted grids in transitionalflow.