An Improved Method For Chemical Non-equilibrium Flow And Its Application

Compared to the solution process of the calorically perfect gas governing equations,the supersonic chemical non-equilibrium flow is a typical space-time multi-scale physics problem,and its governing equations have serious rigidity,which brings great difficulties to numerical solution.Implicit method and uncoupled method are two commonly methods for solving the rigid problem:the time step of the implicit method may not be limited by the stability,but its disadvantage is that the computation amount is rather greater due to the matrix inverse calculation within each time step.The uncoupled method decomposes the multiple physical problems into several sub problems,the computational process avoids the great computation amount caused by the matrix inversion,but the disadvantages are that the numerical instability of different methods will affect the simulation results.By introducing the equivalent energy and the equivalent specific heat ratio in the improved uncoupled method,the governing equations are decomposed into two separate parts of flow and chemical reaction,each part can be solved by its own mature method.On the basis of the improved uncoupled method,this paper continues to simulate the combustion phenomena in supersonic flow,and carries out relevant theoretical research for the purpose of improving the calculation efficiency.The linear transformation of the ordinary differential equations of chemical reaction is carried out to satisfy the solution form of the precise integration method.The precise integration method is used to simulate several numerical examples,and the simulation results are compared with those of the other two traditional methods,which embody the excellent characteristics of the precise integration method to solve the ordinary differential equations of chemical reaction.The flow part governing equation describes the freezing flow of the multi-component mixed gas,according to the nature of the flow phenomenon,the flow operator optimization method is proposed:in the process of updating the flow variables,the component density is updated by the convective fluxand diffusion flux recorded in and out of the adjacent cell boundary,so the calculation efficiency of the flow operator can be improved by reducing the number of equation solution.The classical ballistic target experiment is used to carry out the numerical simulation,and the influence of the flow operator optimization method on the calculation efficiency is reflected by the comparison of the simulation results.The occurrence of chemical reactions needs to meet certain conditions.The mass production rate of the components within the spatial region where no chemical reaction occurs or the reaction reaches equilibrium is close to zero,and the reaction operator spatial adaptive method is proposed by the reaction kinetics theory:the cell satisfying the criterion conditions carries out the iterative solution of the chemical reaction,and the method finally realizes the function of adaptively turning on/off the chemical reaction.This method is used to numerically simulate the combustion problem in supersonic flows.The comparison of results shows that the reaction operator spatial adaptive method has an effect on the computational efficiency.Combining these two methods to test the three-dimensional problem,the calculation results of the chemical non-equilibrium flow simulation method are more close to the experimental data in the supersonic flow problem with lateral jet interference,and the lateral engines are used as the auxiliary device to provide aerodynamic force,which verifies the separation scheme of the TSTO vehicle.The results prove that the method proposed in this paper can be applied to the numerical simulation of practical engineering problems.