Hypersonic Aerothermal Numerical Simulation Method And Massive Parallel Computation Research

Aeroheating has been an important issue for hypersonic vehicles. As hypersonic vehicles fly through the atmosphere, the kinetic energy associated with high velocity is converted into increasing the temperature of the air and into endothermic reactions, such as dissociation and ionization of the air near the vehicle surface. High temperature causes"thermal barrier"and"black barrier"problems which will bring a great impact on the aircraft. Thus we must accurately predict thermal environment and provide guidance and reference for thermal protection.The present dissertation is about research of numerical simulation methods and hypersonic aerothermal computations. Numerical methods were conducted for calorically perfect gas and high temperature thermochemical nonequilibrium gas. Using MPI(Message Passing Interface), parallel methods were developed. Hypersonic computation softwares based on the above methods for the two gas models were coded, and massive parallel computations were carried out for hypersonic aeroheating problem.Eight difference schemes and five limiters are applied in numerical computation of Riemann problem. Performance of each scheme is compared for expansion wave, shock discontinuity and contact discontinuity simulation. Numerical dissipation and it's expediency are discussed. The computation shows that the ability to resolve viscosity and discontinuity is vital to improve scheme's accuracy and quality. The upwind schemes which accord with feature wave propagating direction and avoid the use of artificial viscosity by being inherently dissipative have been the mainstream of current scheme development. AUSM scheme, combining the efficiency of FVS(Flux Vector Splitting) and the accuracy of FDS(Flux Difference Splitting) has favorable properties. MUSCL method is effective to increase computational efficiency and precision. Limiter should be selected appropriately by balancing compressive and diffusive performance.Hypersonic aerothermal simulation method for calorically perfect gas flow is conducted, Grid effect and iteration convergence are investigated using CFD(Computational Fluid Dynamics) method in blunt flow. Grid effect is crucial to aerothermal simulation. Heat transfer prediction is very sensitive to grid spacing in normal direction near the wall. Great temperature grad result in grid sensitivity for heat transfer simulation. The computation showed that the Cell Reynolds Numbers<10 is the effective criterion for computation mesh. Aeroheating computation converged slower than pressure and flow field significantly. When accurate surface-pressure is worked out it can not guarantee converged heat-transfer values. Judging with Machine Zero can guarantee heat flux convergence but is a little time-consuming. Observing convergence of heat flux directly is an effective method. It is considered that viscosity charging in boundary layer induce to slow heat transfer convergence. Hypersonic aerothermal simulation method for High temperature thermochemical nonequilibrium flow is developed. The reacting Navier-Stokes equations including Park's two temperature model, Gupta's air multi-species reaction model and vibrational relaxation were solved to compute aerothermal load. chemical and vibrational source terms are calculated implicitly which diminishs the stiffness of the calculation, accelerates the calculation's convergence. The LU-SGS numerical method with source terms was deduced to do the hypersonic aerothermal computation in thermochemical nonequilibrium flow which improves the calculation's efficiency. The researches on different nonequilibrium models, heat flux constitute and surface catalysis property were discussed. The numerical results are compared to available experimental data, which proved that the proposed methods are of higher-order accuracy.Parallel computation of hypersonic flow field was performed with computational fluid dynamics method. Based on MPI(Message Passing Interface) the CFD parallel aeroheating computation program both for ideal gas flow and high temperature nonequilibrium flow was developed. Multi-blocks parallel aeroheating computation for several cases were performed in PC cluster and high performance cluster system. The computation results indicate that the program and method were acceptable, and could be used for following massive parallel computation and engineering application.