DSMC Method On Cartesian Grid For Rarefied Gas Thermal-Chemical Non-equilibrium Flow

Direct simulation of Monte Carlo called DSMC is a new method developed by Bird used to solve the problems of rarefied gas dynamics.In this paper,three-dimensional DSMC method on Cartesian grid based on the research of Bird is studied.Taking into consideration of thermal-chemical non-equilibrium effects,a set of DSMC numerical simulation program used to solve the problem of hypersonic rarefied gas flow is developed.Firstly,the background and current situation of DSMC method is elaborated.Theoretical bases of molecular gas dynamics and statistical thermodynamics involved in rarefied gas flow are stated.Secondly,Cartesian refinement technique and cutting grid method is used for the generation of Cartesian grid.These two methods improve the accuracy of the calculation and ensure the grid cell fitting properly to the body.An improved neighbor cell search algorithm based on the ray method and binary coded coordinate systems is presented in order to trace the moving of particles in the flow field.Using FROTRAN 90 language and combining revelant models,the DSMC calculation program is developed and numerical experiments are made to verify the correctness of the program.After that,the chemical reaction theory and the equilibrium collision theory are stated.The chemical reaction model of five species is discussed.Combining energy exchange model and chemical reaction model,the code of chemical reaction is writed and numerical experiments are carried out to prove the correctness of the methodFinally,parallel algorithm of DSMC method is studied.The parallel program of DSMC method is developed by using live partition strategy and MPI standard library.Numerical experiments are carried out to verify the efficiency of the parallel algorithm.The DSMC calculation method in this paper can be adopted in the simulation and analysis of the hypersonic rarefied gas flow.It can also be used in the calculation of reentry process of the hypersonic vehicles in the environment of Earth,which has reference value and guidance significance for the engineering design.