Numerical Simulation Research On Areodynamic Heating And Structure Heat Transfer In Rarefied Flow

Aeroheating has been the issue of great concern to designers for a long time.As hypersonic vehicle flies in high altitude,air temperature near the vehicle surface increases sharply because of severe compression.Air heat transfers to the vehicle surface by convection and shock radiation,which has great influence on intension and stiffness of the vehicle structure.Accurate prediction of aerodynamic thermal environment and structure temperature during aeroheating can provide technical support for vehicle design on the thermal protection systems and aerodynamic heating characteristics analysis.Hypersonic vehicle’s heating problems in rarefied flow are studied by use of numerical simulation methods.The influences of gas-surface interaction models and chemical reaction on thermal characteristics are analyzed in detail by use of Direct Simulation Monte Carlo(DSMC)method.Efficient processing technologies are presented to improve simulation efficiency for DSMC method.A coupling method is presented to deal with hypersonic vehicle’s heating problem in rarefied flow by combination of DSMC and structure heat transfer calculation method.First of all,molecule kinetic theory of gas and implementation of unstructured grids DSMC method are studied.Rarefied gas dynamics theory is discussed from velocity distribution function,description of macrocosmic gas,mechanical mechanism of binary elastic collision and so on.Principles and key technologies of DSMC method are discussed in detail.Unstructured grids DSMC calculation program is coded and some numerical examples are presented.Secondly,influence of gas-surface interaction models on thermal characteristics for hypersonic rarefied flow is studied by use of DSMC method.A wall boundary condition based on radiative equilibrium is developed,which overcomes the defects of isothermal boundary condition and can provide more precise wall temperature distribution during numercial simulations.The specular reflection boundary model,diffuse reflection boundary model and Maxwell reflection boundary model coupled with diffuse reflection and specular reflection are analyzed and applied in this paper.The influence of different temperature wall boundary conditions and gas surface reflection boundary models on aeroheating are compared and analyzed in detail by extensive numercial examples.Then,chemical reaction influence on thermal characteristics for hypersonic rarefied flow is studied.The chemical reaction rate constant and Bird’s phenomenological chemical reaction model are expounded.In the meantime,the reaction probability function of different collision models is deduced.Reaction mechanism and implementation of composite,replacement and dissociation reactions in five species high temperature gas are discussed.Eleven species gas model DSMC method is developed based on five species gas model DSMC method.A bundling method is used to deal with electron motion,in which every electron particle is tied directly to the ion it is born with.By comparing specific numerical experiments with other’s results,unstructured grids DSMC codes with five species gas model and eleven species gas model are validated.Then,numerical experiments are made to investigate the chemical reaction influence on rarefied thermal characteristics by use of different mixture gas models.Afterwards,a coupling method is presented to deal with hypersonic vehicle’s heating problem in rarefied flow.The DSMC method is combined with heat conduction equation by introduce of Newton cooling law.An efficient loose coupling procedure is designed to calculate the temperature distribution of thermal protection system.Numerical experiments are made to simulate structure temperature and heat flux distribution characteristics.Based on the coupling method,chemical reaction influence on structure heat transfer calculation is also studied.At last,efficient processing technologies are presented to improve simulation efficiency for DSMC method.An adaptive collision distance collision pair selection method is developed,which can relax the cell size constraint and maintain the fine simulation resolution.An adaptive molecule time step approach is developed,which can reduce the computing time significantly.Parallel algorithm of unstructured grids DSMC method based on the MPI standard message-passing library is investigated.Parallel computing is used to replace the traditional serial computation and the calculating efficiency is improved greatly.The corresponding calculation programs are coded and some numerical simulations are made.