DSMC方法中的自适应当地时间步长法

理论分析表明,Laux提出的DSMC(Direct Simulation of Monte Carlo)方法中的当地时间步长法尽管能够显著缩短流场达到稳定所需的CPU计算时间,提高DSMC程序的运行效率,却存在仿真分子运动和碰撞计算复杂,并需要耗费额外计算机内存的缺憾.对Laux的方法中仿真分子的运动处理时机提出了改进,并改变了其碰撞抽样方法,从而简化了仿真分子的运动和碰撞计算处理,避免了额外的计算机内存消耗.应用改进后的自适应时间步长法,对圆柱的稀薄气体绕流进行了采用和未采用改进的自适应当地时间步长法的对比计算.结果表明,改进后的自适应当地时间步长法能明显缩短流场达到稳定所需的计算时间,对流场模拟结果产生的影响却非常小.

Adaptive local time step method for DSMC code

Theoretic analysis reveals that,ALTS(adaptive local time step) method offered by Laux,although greatly reducing the execution CPU time needed for the flow to reach to a steady state and thus leading to high simulation efficiency of DSMC(direct simulation of Monte Carlo) method codes,has some drawbacks in complicating molecules' moving and collision calculations and in requiring additional RAM.Modifications were made to time intervals at which molecular moving and collision are computed,and to the collision sampling method.These modifications simplified molecules' moving and collision computation,and also avoid the consumption of unnecessary RAM.The modified ALTS method was adopted in the DSMC code.Simulations of rarefied gas flow over a cylinder were performed with and without this modified ALTS method,and the result shows that these modifications result in a significant reduction in the execution CPU time,but introduce little difference on the simulation resolution and the flow structure.