Hypersonic nonequilibrium flow simulations over a blunt body using bgk simulations

Abstract

There has been a continuous effort to unveil the physics of hypersonic flows both experimentally and numerically, in order to achieve an efficient hypersonic vehicle design. With the advent of the high speed computers, a lot of focus has been given on research pertaining to numerical approach to understand this physics. The features of such flows are quite different from those of subsonic, transonic and supersonic ones and thus normal CFD methodologies fail to capture the high speed flows efficiently. Such calculations are made even more challenging by the presence of nonequilibrium thermodynamic and chemical effects. Thus further research in the field of nonequilibrium thermodynamics is required for the accurate prediction of such high enthalpy flows. The objective of this thesis is to develop improved computational tools for hypersonic aerodynamics accounting for non-equilibrium effects. A survey of the fundamental theory and mathematical modeling pertaining to modeling high temperature flow physics is presented. The computational approaches and numerical methods pertaining to high speed flows are discussed. In the first part of this work, the fundamental theory and mathematical modeling pertaining to modeling high temperature flow physics is presented. Continuum based approach (Navier Stokes) and Boltzmann equation based approach (Gas Kinetic) are discussed. It is shown mathematically that unlike the most popular continuum based methods, Gas Kinetic method presented in this work satisfies the entropy condition. In the second part of this work, the computational approaches and numerical methods pertaining to high speed flows is discussed. In the continuum methods, the Steger Warming schemes and Roe’s scheme are discussed. The kinetic approach discussed is the Boltzmann equation with Bhatnagar Gross Krook (BGK) collision operator. In the third part, the results from new computational fluid dynamics code developed are presented. A range of validation and verification test cases are presented. A comparison of the two common reconstruction techniques: Green Gauss gradient method and MUSCL scheme are discussed. Two of the most common failings of continuum based methods: excessive numerical dissipation and carbuncle phenomenon techniques, are investigated. It is found that for the blunt body problem, Boltzmann BGK method is free of these failings.