Numerical Simulation Of Hypersonic Fluid-Thermal-Structural Coupled Problem

With the rapid development of aircraft technology,hypersonic vehicle has been highly valued by countries around the world since the beginning of twenty-first Century.One of the key problems in hypersonic flow is aerodynamic heating.Aerodynamic heating will bring abouttemperature rise and change of temperature distribution in structure.Temperature rise may change the material properties of structure,while the uniform temperature field will cause structural thermal stress.All of these may change the structural stress,stiffness characteristics and the modal.They have a significant influence on the structural static / dynamic aerothermalelastic properties.In most cases,this effect is harmful and cannot be ignored.In the aspect of reusable hypersonic cruise / orbit vehicle,the United States is the world's most advanced country.Falcon,HyTech,Hyper-X and other plans have been put forward successively in last decade years by this country.Many significant technical difficulties in predicting the structural response under extreme environment have been pointed out,such as fluidthermal-structural coupling,large and complex coupling model,computational cost and so on.In this thesis,the research worksabout some key techniques have been carried out for fluid-thermal-structural coupling problem.They contains space-time discretization methods and moving mesh in aerodynamic force/heating calculation,physics model and interface interpolation methods in aero-structural thermal numerical simulation,analytical procedure and gridprocess in static aerothermoelasticity,and aerothermoelastic analysis processwhich includes unsteady aerodynamic heating and dynamic analysis under the modal coordinates in trajectory states.The main contents are as follows:Firstly,the numerical simulation method and program have been developed for the calculation of flow field,structural temperature distribution and structural stress field.The simulation program for fluid field is suitable for steady / unsteady high-speed compressible aerodynamic force and aerodynamic heat simulation.This program is based on hybrid/unstructured finite volume method.Convective fluxes are computed using JST and AUSM scheme.The one equation model,S-A model,is available for turbulence model.In terms of time step,a multi-step Runge-Kutta iteration scheme is used in steady states while a dual-time step method adopted in unsteady states.The dynamic grid technology is also introduced.Structural temperature field numerical simulation is based on the finite volume method.Temperature gradient calculation method includes the least square method and Green Gauss method.The time approach scheme is the same as the flow field numerical simulation method.For structural numerical simulation,the isoparametric elements are adopted.The SOR methods,GMRES methods and CG methods are used to solve the linear equations.Several test cases are studied using above three programs.The numerical model,schemes,calculation accuracy and etc.of three programs are verified.The convergence efficiency of different methods for solving linear equations are compared.Then an aero-thermal and structural-thermal integrated numerical simulation method is presented.It can be used for 2d/3d,steady/unsteady aerodynamic heating and structural heat transfer coupled problem.A unified integral equations system is developed as the control equations for physical process of aero-heating and structural heat transfer.The whole physical field is discretized by using a finite volume method.The corresponding calculation methods are given to work out the value of the temperature,the temperature gradient and the heat transfer coefficient on the boundary between fluid and structure.The effect of grid across the interface of structure and fluid on the calculation accuracy is studied.The results show that if the grid size is too large,the calculation may be not accurate,and if it is too small,the amount of computation will be greatly increased.Through the comparison of the coupling algorithm and the integration algorithm,it can be found that the sensitivity of the integrated algorithm to the grid is smaller than that of the coupling algorithm.Based on the aero-thermal and structural-thermal integrated numerical simulation method presented in chapter 3,a new method for aerothermoelastic analysis has been developed by combining the structural static finite element method.Static aerothermoelasticity calculation for two-dimensional wing is carried out.The effects of temperature rise and angle of attack on static aerothermoelasticity are investigated.The structural stress and strain distribution with uniform temperature rise and non-uniform temperature rise are compared.The results show that when the temperature rises up to order,the lift and drag coefficient will be greatly influenced.In the design of hypersonic vehicle,the accurate prediction of the temperature distribution is very important to the structural design,and the influence of the thermal stress caused by non-uniform temperature rise must be considered.Aero-thermal and aerothermoelastic methods for hypersonic aircrafts in trajectory state are presented.The aerothermal method,which considers heat transfer process in thermal protection structure by coupling one-dimensional heat transfer equation,is based on combination Euler solution and engineering approach.Aerothermoelastic analysis will be carried out after model analysis of thermal structure.Aerodynamic heating of X-37 B class hypersonic aircraft in trajectory state is analyzed.The results show that the outer surface temperature will change sharply and the inner temperature change moderately with time in this trajectory.The chemical reaction effect makes a difference to the aerodynamic heating.It may reduce the highest temperature in the structure.The analysis of the aerothermoelastic behaviors in one state of the trajectory shows that the temperature rise caused by aerodynamic heating reduces the structural inherent frequency and has little effect on structural modal.Finally,a review of this thesis is made and the direction about the future research is presented.