Dynamics of Gas Molecule near the Surface in Rarefied Flow

1)用分子动力学方法模拟了气体分子在有吸附气体分子的表面上的散射过程。散射过程有4种模式，它们与气体分子向其它分子的能量传递分布有关。通过改变气体分子的质量比、势能系数、表面吸附质数等参数，研究了散射过程对气体分子粘附和逃逸动力学的影响。2）为了研究气体分子在热平衡状态下的粘附和逃逸动力学，对氙分子在两片铂片之间的行为进行了长时间的数值模拟。逃逸过程有三种类型。其中两个是由吸附气体分子的相互作用引起的。3）用“直接模拟蒙特卡罗”方法估算了表面粗糙度对稀薄气体流动的影响。测试用例是两个板之间的库埃特流。一块板有一些粗糙度，模拟了车床切削齿的形状。在高Knudsen数下，粗糙度的影响通过粗糙度尖端的涡结构而达到整个流场。对粗糙度、咬入角和努森数进行了参数研究。

1) Using the molecular-dynamics simulation method, the scattering process of gas molecule on the surface with adsorbale gas molecules. There are 4 patterns of scattering process, that associated with the distribution of energy-transfer from gas molecule to other molecules. The parameters such as mass ratio of gas molecule, potential coefficients, number of adsorbate on surface are changed in the simulation, and their dependency on the scattering process is studied.2) To study the sticking and escaping dynamics of gas molecule in thermal equilibrium stale, the behavior of Xenon molecules between two plate of Platinum are simulated for a long period. The escaping process has three types. Two of them are caused by interaction from adsorbated gas molecule. Also the dependency of escaping molecules on the coverage coefficients are studied.3) The effrect of roughness of the surface to rarefied gas flow is estimated by "Direct Simulation Monte Carlo" method. The test case is Couette flow between two plates. One plate has some roughness that simulate the shape made by cutting bite of the lathe. With high Knudsen number, the effect of roughness reaches to all the flow field by some vortex structure at the sharp edge of roughness. The parameter study is done on the height of roughness, angle of bite, and Knudsen number.