Study Of Aerothermoelastic Modeling And Analysis

The airbreathing hypersonic vehicle(HSV)and reusable launch vehicle(RLV)have a long-duration flight in the severe aerodynamic heating environment which changes the properties of the materials,varies the structural inherent characteristics and leads to the reduction of the structural stability.Therefore,the time-varying and nonlinear features of the aircraft under the combined action of the high temperature,high dynamic pressure make the nonlinear aerothermoelastic problem remarkable.Thus the aerothermoelastic analysis is becoming one of the key techniques in the design of the HSV and RLV.The aerothermoelastic analyzing system is composed by the coupling of nonlinear aerodynamics(aerodynamic heating)/ heat conduction / structural dynamics which is called by three-field coupling.This paper aims at modeling the nonlinear aerothermoelastic system and solving the coupling of nonlinear aerodynamics(aerodynamic heating)/ heat conduction / structural dynamics,and the main reaseach results are as follows:(1)A CFD solver is programmed to solve hypersonic flow.In the modeling of high temperature chemical reaction,the combination of equilibrium constant method and Hermite interpolation is used to calculate the thermodynamic and transport properties,which reduces the computational cost in CFD compared with equilibrium constant method and avoids the shortcoming of the piecewise fitting in continuity.After that,the Menter's SST turbulence model,Ausmpw+ scheme and LUSGS method are implemented in the CFD program to solve the hypersonic flow.Besides the grid smoothing and orthogonalizing process by solving Laplace equations is adopted to preserve the accuracy in the calculating of aerodynamic heating.Then the developed CFD program is verified by test cases and the results show good agreement with the reference resources.(2)The temperature and displacement of the heated structure are solved by the programming implementation of the finite element method(FEM).In temperature calculation,the non-physical oscillation is avoided by using lumped heat capacity matrix and the computation efficiency is improved by the PCG method.In structural displacement computation,the thermal effects are considered while the geometric nonlinearity is taken into account without extra effort.The results of typical examples are in good agreement with the results of the analytical method and the commercial software.It is proved that the developed finite element solver has a good accuracy in solving the temperature and the displacement.(3)A finite element interpolation(FEI)method based on the inverse isoparametric mapping is developed to realize the transfer of pressure,deformation,heat flow and temperature on different grids in a unified processing.This method overcomes the disadvantage of the conventional global interpolation method in efficiency and treatment of discontinuous variables,and avoids the complexity of the implement of surface interpolation and body interpolation in three-field coupling by a variety of interpolation methods.The grid deformation method which is achieved by combination of RBF extrapolation,FEI projection and TFI technique featured in shape preserving is proposed to solve dynamic grid problem of discontinuous compound deformation of combinations in unsteady analysis.(4)Four aerothermoelastic coupling strategies are proposed,namely,unsteady two-way coupling strategy,unsteady one-way coupling strategy,quasi-steady two-way coupling strategy and quasi-steady one-way coupling strategy,and the solving processes and numerical simulation methods of the four coupling strategies are given respectively.Two universal,easy-to-use and efficient initial value calculation methods are proposed to solve the connecting problem between unsteady aerothermal coupling and unsteady aeroelastic coupling in the unsteady one-way coupling strategy.The influence of two-way coupling and unsteady effects of the four strategies is analyzed theoretically meanwhile the application scope for each coupling strategy is provided.(5)With the four kinds of the three-field coupling strategies above,the aerothermoelastic analysis of a low-aspect-ratio wing and a panel are carried out.The application scope of each coupling strategy is given by comparing the results under different coupling strategies: 1)The unsteady 2-way coupling strategy has the most comprehensive ability to simulate physical field in aerothermoelastic analysis.It is suitable for calculating temperature field,coupled deformation response and load,while it can be used for thermal flutter analysis.However,the computational cost is large,and it needs to be parallelized and migrated to high performance computing cluster for engineering application.2)The unsteady one-way coupling strategy is suitable for calculating coupling deformation and load,analyzing thermal flutter analysis,and obtaining the frequency and amplitude of vibration after thermal flutter.However,it is only suitable for temperature field calculation on the premise that structural deformation has little influence on the aerothermal coupling calculation.3)Quasi-steady 2-way coupling strategy is only applicable to calculate temperature field,quasi-steady structural deformation and load before thermal flutter occurs,and can not be used for thermal flutter analysis.The application premise for this coupling strategy is that the quasi-steady deformation is almost located in the center of the unsteady deformation.4)The quasi-steady one-way coupling strategy is only applicable to calculate the quasi-steady structural deformation before thermal flutter occurs,and can not be used for thermal flutter analysis.The application to calculate the temperature field is on the premise that structural deformation has little influence on the aerothermal coupling calculation.This coupling strategy can only be applied when both quasi-steady assumption and one-way coupling assumption are valid at the same time.