【作者】 冯萍；

【导师】 梁德旺； 黄国平；

【作者基本信息】 南京航空航天大学 ， 航空宇航推进理论与工程， 2006， 硕士

【摘要】 DSMC方法为数值求解稀薄气体动力学问题有效方法。所以本文根据该算法发展了一套计算二维微尺度流动的数值计算程序FSMM2D(Flow Simulation based on Molecule Movement, 2-Dimensional),并针对微尺度流动的特点进行了相关的改进研究。首先,编程实现了基本DSMC方法对二维流动的计算,给出了所用算法的原理、相关模型,并结合程序结构流程图,分别介绍了初始化流场、计算分子的运动、边界的处理、分子的排序、抽样计算分子的碰撞、流场参数采样统计各个功能模块在FSMM2D中的实现,并对该程序进行了算例校验。其次,分析推导了特征波理论用于处理DSMC算法边界条件的过程。并针对影响程序计算的主要特征参数(采样循环数、模拟分子数、子网格数)进行研究,对采样循环数、模拟分子数、子网格数对计算结果的准确性和所耗机时进行了分析比较,结果表明:采样循环数的取值多少不仅会影响计算的准确性还会影响计算机时,本文建议取在8左右为宜;单位网格内粒子数太少会增加总循环步数从而增加计算时间,太多虽不增加总循环步数,但每个循环耗时增加,也会增加计算时间,故单位网格内粒子数选取应该适中,本文建议取为5个左右为宜;子网格数对流场计算结果的准确性一般没有影响,但是对运算时间影响很大,取得恰当能节约计算时间,取4时最节约计算时间。然后,分析了DSMC产生统计噪声的机制,采用信息保存技术有效抑制了计算的统计噪声,保证计算的准确性且提高了计算收敛速度。通过微尺度通道低速流动模拟效果的对比,验证了DSMC-IP算法比原算法的准确性和速度都有明显提高。最后,为了拓宽本文发展的数值计算二维微尺度流动程序的使用范围,使其具备能够模拟不规则复杂形状流场的能力,讨论分析了可对任意几何形状、多块结构化网格进行计算的相关算法。更多还原

【Abstract】 Two dimension flow simulation based on molecule movement (FSMM2D) is presented in this paper, which is developed from DSMC method.Firstly the basic concepts and theories of DSMC have been introduced. Then a general description of FSMM2D is provided. With the flowchart the program can be divided into six parts and it includes initial flow field, computation of molecular motion, boundary treatment, re-sort of molecular, sample and computation of molecular collision. Several cases have been simulated to certify the correctness of the program.DSMC method is improved using method of characteristics to modify the boundary condition and gets the goal as expected. Investigations on the selection of three key parameters are carried out. Results show that the best values for the number of sampling loop、the number of simulated particle per cell and the number of sub-cell are about eight、five and four respectively. Micro-plate layer, and flow through micro vertical plate are simulated and it is clear that the improved program with the optimal parameters can not only get the same results as those of other researchers but can greatly enhance the computational accuracy and efficiency.DSMC method inherently involves the restriction of statistical noise problem and IP method is an improvement algorithm of DSMC method. Descriptions of suppression of statistical noise and algorithm realization of IP method are provided. DSMC-IP method is a reasonable and reliable tool for simulation of low velocity micro flow through comparing and verifying several cases. Moreover, the advantage of this method is obvious and outstanding in computational resolution and efficiency.At the end of this paper the feasibility and possibility to enlarge the range of application of DSMC-IP method to structural grid with curvature geometry are discussed.更多还原