Design And Thermal-Mechanical Analysis Of Corrugated-Core Integrated Thermal Protection System For Hypersonic Vehicle

With the development of hypersonic reusable vehicle,the integrated thermal protection system(ITPS)should satisfy the characteristic of light weight,cost effective,bearing aerodynamic and easy maintenance.From the point of structure design,the preliminary design method of ITPS and the thermo-mechanical problem involved are studied,and an optimization design method of ITPS is developed.The main contents of the paper include the following aspects:(1)A rapid design method for ITPS is present,which combines the vehicle geometry and trajectory data with radiation equilibrium equation to determine the area of ITPS and select the proper structural material.In order to reduce the computational cost,the method of extreme design situation is present,and the geometry of ITPS is optimized in the extreme design situation.The design method involves the calculation of heat transfer,static response and stability for ITPS.(2)For the problem of heat transfer,a novel approximate analytical method based on separation of variables and orthogonal expansion technique is presented for temperature prediction through ITPS subjected to convection and radiation boundary conditions,which considers the effects of temperature-dependent thermal material properties.The ITPS is simplified as a sandwich plate,and an advanced linearized approximation for radiation boundary condition is developed for modified use with the analytical model.The proposed method applies a set of linear functions with space-variable to describe the distribution of thermal diffusivity through the thickness direction,and it adopts a numerical solution dividing the whole process of heat transfer into a chosen number of time steps to solve the problem of boundary conditions variation with time.The exact solution composed of Bessel and trigonometric functions can be derived.For the new heat transfer function described by linear functions,the orthogonality property of space-variable function is proved.(3)For the problem of static analysis for ITPS,a C~0 higher-order layerwise finite element model combined with homogenization techniques is presented.The ITPS panel is homogenized as an equivalent sandwich plate,and a reduced temperature field for the entire panel is derived.An advanced analytical equivalent model based on energy approach for the mechanical properties of the trapezoidal corrugated core is presented,which considers the effects of temperature-dependent material properties.The proposed layerwise theory which is developed for a sandwich plate,assumes linear,quadratic and cubic polynomial distributions of displacements for middle layer and linear polynomial distributions of displacements for top and bottom layers,and the finite element is developed to model the equivalent sandwich plate.The effect of transverse normal strains is taken into account in the layerwise theory.(4)By employing the high-order layerwise theory and the principle of structural mechanics,the stress distributions in ITPS under thermal and mechanical loads are predicted.The method considers the effects of temperature-dependent material properties and curvature in sheets.The local displacement induced by out-of-plane pressure is taken into account for the top face sheet,and the local displacement of the bottom face sheet induced by corrugated webs is also considered by treating the sheet as beams with proper displacement compatibility.According to the ITPS is a periodic structural plate,a simplified three-dimensional finite element model is present,which can reduce the time of buckling solution.And the boundary conditions of simplified model are applied by the symmetric structure of corrugated core.(5)For the problem of dynamic response of ITPS,a finite element model is created for calculating the natural vibration frequencies and shapes.The influence of temperature dependent material properties and thermal stresses are taken into account in the model.And the hypothesis of geometry nonlinear is considered,when the structure buckling occurs.The effects of temperature environment on the dynamic properties of ITPS are studied by using the finite element model.Otherwise,a transient finite element method for solving thermo-mechanical coupling based on Galerkin and Newmark algorithm is established,and the hypothesis of geometry nonlinear is also considered.And the effects of coupling term on the transient response are studied by applying the method.Finally,based on the study of the design method for ITPS and the calculation method involved,it is applied to the preliminary design of the hypersonic reusable aircraft.Through design examples of space shuttle and RBCC,the correctness of the design method developed in this paper can be verified.The paper aims to provide a better method for promoting the application of ITPS in hypersonic vehicle,which puts the foundation for the development of hypersonic reusable vehicle.