DSMC Method And The Optimization Techniques For Cut-cell Cartesian Mesh

As science and technology advances, the technology in Aeronautics and Astronautics field develops rapidly. Aircraft not only break through the tradition in configuration and structure, flight altitude is also rising. With the rising of flight altitude, the gas density is getting smaller and smaller, rarefied gas effect has become increasingly evident. In this case, under the assumption of continuous media Navier-Stokes equation is no longer applicable, and it is replaced by highly nonlinear Boltzmann equation. Using numerical method to solve Boltzmann equation is extremely difficult, in order to facilitate the study of the equation, a variety of hypotheses are often needed. In order to effectively solve the problem of rarefied gas dynamics, it has developed a series of methods. In these methods for solving the rarefied gas dynamics, the direct simulation Monte-Carlo method(DSMC) which was proposed by Bird develops rapidly. It is widely used, and has been one of the most important way for rarefied gas dynamics study. This paper studies the hypersonic rarefied gas flow DSMC Method based on cut-cell Cartesian mesh and is committed to develop a set of high degree of automation and good universality, suitable for cet-cell and any complex shape DSMC program.In this paper, the basic principles of molecular gas dynamics are elaborated firstly, laying the foundation for direct physical simulation of rarefied gas flow. Secondly, through the cut-cell to ensure the body fitted properties of grid cell, while using mesh refinement technique to meet the requirements of mesh scale near the surface. Such a cartesian mesh generation method not only improves the search efficiency, but also ensures the accuracy of the computation near the surface. Then we study the implementation and application of DSMC method based on cut-cell cartesian mesh, and develop a new adjacent cell search method which can be applied to molecules search between polyhedrons with arbitrary shape. Because the DSMC method is a statistical method for the study of molecules, the requirement of computer resources is extremely high. So, this paper finally studies the local simulation molecules represent real molecular number and dynamic time step two optimization techniques to improve the computational efficiency of the program, and prove the correctness of these methods through the calculation example.