航天器表面环境散射返回流污染数值模拟和影响因素分析

针对航天器表面出气分子形成的环境散射返回流污染问题,利用试验粒子Monte Carlo方法对圆球和圆柱体简化航天器表面环境散射返回流进行数值模拟。其中,圆球出气表面的计算结果与已有的DSMC(Direct Simulation Monte Carlo)方法计算结果一致,验证了该方法的正确性。此外,对不同长径比的圆柱表面环境散射进行了计算和分析,结果表明:来流方向垂直于圆柱对称轴时,返回分子主要分布在圆柱体侧面的迎风部位;返回通量比随来流与出气分子质量之比的增加逐渐减小,随来流与出气表面温度之比、来流分子速度比和数密度的增加而增大;不同长径比条件下返回通量比相对于上述4个参数的变化具有相似性和递变性,短粗体的返回通量比最小,长细体的最大,正常圆柱体的则居中;返回通量比相对来流攻角的变化在不同长径比条件下不再具有相似性,而是取决于有效迎风面积。

Numerical simulation and physical analysis of return flux on spacecraft surfaces due to ambient scatter of outgassing molecules

The test particle Monte Carlo (TPMC) method is used to determine the return flux on spherical and cylindrical simplified spacecraft surfaces due to ambient scatter of outgassing molecules. The return flux ratio (RFR) obtained for the flows past a sphere is in a good agreement with that acquired by the direct simulation Monte Carlo (DSMC) technique. The computation and the analysis of the return flux on cylindrical simplified spacecraft surfaces with different length-to-radius ratios due to ambient scatter show that the most returned molecules are distributed in the up-wind regions on the side surface of the cylinder. In addition, the RFR is increased with the decrease of the ratio of the freestream molecular mass to the outgassing molecular mass, with the increase of the ratio of the freestream temperature to the temperature of the outgassing surfaces, and with the increase of the freestream molecular speed ratio and the number density. The variations of the RFR with the four aforementioned parameters at different length-to-radius ratios are similar, and the RFR for the slenderest cylinder is the maximum, the RFR for the dumpiest geometry the minimum, and the RFR for the moderate-size geometry takes values in between. Depending on the effective up-wind area, the variations of the RFR with the freestream angle of attack at different length-to-radius ratios are no longer similar.