两种用于NS-DSMC耦合方法的连续失效参数对比

NS-DSMC（Navier Stokes-Direct Simulation Monte Carlo）耦合方法是计算连续-稀薄跨流域流动的主要方法，应用过程中如何确定连续流域和稀薄流域的界面是此方法的关键问题之一，界面位置通常通过连续失效参数来判定.为合理选择连续失效参数，对目前广泛使用的两种连续失效参数Kn_Q和B参数进行了理论上的分析和比较，表明虽然他们建立的出发点不同，但在数学形式上具有一定相似性.通过圆柱绕流问题的数值试验进一步验证了两种连续失效参数具有一定对应关系.Kn_Q和B两种连续失效参数在NS-DSMC耦合方法中应用效果相差不大，但Kn_Q 的阈值0.05适用范围较广，而B参数的阈值对不同流动问题会有变化. 

Comparison analysis between two continuum breakdown parameters applied in coupled NS-DSMC method

Navier Stokes-direct simulation Monte Carlo (NS-DSMC) coupled method is a principal method for the computation of continuum-rarefied transitional gas flows. How to locate the interface between continuum and rarefied domains is one of the key aspects in using this method, which is generally achieved by applying a continuum breakdown parameter. To choose the continuum breakdown parameter more reasonably, theoretical analysis and comparisons were carried out for two major continuum breakdown parameters: Kn_Q and B, which show that they have similar mathematical forms to a certain extent, although they are established from different basis. Numerical test was conducted by using an over-cylinder flow problem which also indicates the relationship between them. Kn_Q and B parameters have few differences when applied in NS-DSMC coupled method, except that Kn_Q parameter has a widely used threshold value of 0.05, but the threshold value of B parameter will vary for different flows.