Theoretical and numerical studies of rarefied hypersonic flows

In this dissertation a comprehensive work on theoretical and numerical studies of rarefied hypersonic flows is presented. On the theoretical part, gaskinetic study and exact solutions are obtained for problems related with high speed collisionless round jet: expanding into a vacuum; impinging at a normally set, diffuse or specular reflective plate with finite radius. Several fundamental geometry-velocity relations are utilized in this study and they play crucial roles. These complete results include flowfield properties, and impingement properties at the plate surface. The final results include complex but accurate integrations involving geometry and specific speed ratio factors. Several numerical simulations with the direct simulation Monte Carlo method validate these analytical exact results.;In the numerical part, a multi-dimensional gas-dynamical computational scheme package named GRASP-K ("G&barbelow;eneralized R&barbelow;arefied gA&barbelow;s S&barbelow;imulation P&barbelow;ackage - K&barbelow;inetic") is presented. This implementation adopts a concept of simulation engine and it utilizes many Object-Oriented Programming features and software engineering design patterns. As a result, this implementation successfully resolves the problem of functionality and interface conflictions for multi-dimensional Gas Kinetic Scheme implementations. The package has an open architecture which benefits further development and code maintenance. This package can utilize traditional structured, unstructured or hybrid grids to model multi-dimensional complex geometries and multi-species hypersonic thermo-chemically nonequilibrium gas flows. A preliminary test case of a two-species hypersonic flow passing a cylinder and some preliminary results are obtained. The pressure distribution of the gas mixture along the cylinder wall is compared with those in previous works.;A Navier-Stokes equations based computational fluid dynamics solver is also incorporated in the package to simulate hypersonic nonequilibrium flows. This solver includes comprehensive chemical reaction models and thermodynamics relations and the phenolic-silica ablation flow simulation is considered. Finite rate chemical reactions, multiple temperature relaxation processes, and ionization phenomena are modeled. Hence the package can be used to simulate multiple-dimensional, non-equilibrium gas flows with multiple-species. Simulation results of several hypersonic gas flows over blunted bodies are presented and compared with results in the literature.