Numerical Method Of Simulating Hypersonic Chemical Non-equilibrium Flow-fields On Hybrid Grid

The near space vehicles have been paid more and more attention in recent yearsall over the world. During the long time flight with very high velocity in the nearspace, the vehicles will face serious real-gas effects problem, since the temperature onthe surface is very high (up to thousands degree). It is very difficult to simulate thereal flight environment in hypersonic wind tunnels. Therefore, the CFD(Computational Fluid Dynamics) methods are becoming a very important tool in thestudy of aerodynamic performance in near space. On the other hand, theconfigurations of near space vehicles become more and more complex, which resultin the challenge of the generation of high-quality of computational grids. Thestructured/unstructured hybrid grid generation technique represents the trend of gridgeneration techniques over complex configurations. Hence, it is necessary to developthe numerical methods of thermo-chemical non-equilibrium flow fields based onunstructured/hybrid grids. In this dissertation, a numerical method of thermo-chemicalnon-equilibrium flow fields on hybrid grids is presented, and the numerical methodsof chemical source terms are compared with in some typical cases. The purpose ofthis dissertation is to enhance the ability of our CFD code to simulate ofthermo-chemical non-equilibrium flow fields over complex configurations.There are six chapters in this dissertation.The first chapter is the introduction, in which the physical significance andengineering background of CFD in simulating chemical non-equilibrium flows onunstructured grids and hybrid grids is introduced, and the progresses in recent years,including the numerical methods, the grid generation techniques and somewell-known CFD software in this field, is reviewed. And finally, the present work ofthis dissertation is summarized briefly.In the second chapter, the numerical methods adopted in this paper are introduced,including the governing equations, the thermodynamic and chemical models,numerical schemes (such as the flux splitting schemes, the limiters for stability andboundary conditions).The validation of the numerical methods is done in the third chapter. Fourbenchmark cases are tested, including the laminar flow over a plate, hypersonic flowover a cylinder, and the classical shock-induced combustion problem over a sphere.The numerical results are compared with analytical solutions or experimental data, such as the distributions of the pressure coefficients (Cp), the skin friction (Cf). Theresults demonstrate the ability of simulating the chemical non-equilibrium flows.In the fourth chapter, the applications on structured/unstructured hybrid grids arecarried out. The typical cases of air reaction are simulated on two-dimensional andthree-dimensional hybrid grids.In the fifth chapter, the numerical schemes of chemical source terms are studiedand compared with each other. The numerical results show that, for some cases, theimplicit scheme of the chemical source terms is necessary to enhance the convergencehistory, however, for other cases, the implicit approach seems to be invalid. So,further study should be carried out in the future.Chapter six is a brief conclusion, and the future work is discussed also.