Research On Mars Rarefied Flow Through DSMC Numerical Technique

This paper studies the flow field around hypersonic vehicles when reentering the rarefied atmosphere of Mars in Mars explorations. By adopting the Direct Simulation Monte-Carlo?DSMC? method and taking into consideration of thermal-chemical non-equilibrium effects, a set of DSMC numerical simulation program is developed.Firstly, environmental characteristics of Mars and key exploration technologies are analyzed. The DSMC method is then used in this paper to simulate the flow field of the Mars atmosphere because of its highly rarefied characteristic.Secondly, theoretical bases of molecular gas dynamics and statistical thermodynamics involved in DSMC method are stated. The algorithm implementation process and applications of DSMC method are detailed introduced. With some calculation cases, the basic DSMC simulation code is verified. According to the application experiences of DSMC method, some suggestions in mesh generation, simulation number of molecules and calculation load prediction are taken in this paper.After that, the realization of DSMC method in Mars chemical reactions is studied. The vibration modes of CO₂ molecule are analyzed, and implementation method of polyatomic molecule vibrational energy relaxation is given. The chemical reaction model for the Mars atmosphere is proposed and implanted in the DSMC method. A set of calculation code for the simulation of Mars rarefied chemical reaction flow is developed and then validated under different components reaction cases. And Mars thermal-chemical non-equilibrium effects are investigated.Finally, based on the calculation code stated above, the influence of the gas rarefaction on the flow field is studied and the variation pattern of the flow field with different Knudsen number is summarized. Then on this basis, an empirical method for the prediction of rarefied flow field is proposed, and the location of shock waves in hypersonic cylinder flow is successfully predicted by using this method.The calculation method proposed in this paper can be adopted in the simulation and analysis of the hypersonic rarefied flow; it can also be used in the calculation of the reentry process of the hypersonic vehicles, which has certain guiding significance for the future engineering design.