The Research On Prediction Method Of Equivalent Thermal Conductivity Of Porous Media

Due to aerodynamic heating,the surface temperature of a hypersonic vehicle can exceed3000 K when flying at a high Mach number.To maintain the safety of internal instruments,thermal protection is very important.Porous media is widely used in thermal protection systems for it has many advantages such as lightweight and good heat insulation performance,which is often used as ablation material at the tip of aircraft and heat insulation material for active cooling systems.Due to the complexity and randomness of the internal structure of porous media,the concept of equivalent thermal conductivity is introduced for better describing its thermal conductivity.Traditional methods have low efficiency and poor adaptability in calculating the equivalent thermal conductivity of porous media.To accurately predict the heat transfer performance of porous media or thermal protection systems containing porous media,it is promising to use the inverse heat conduction problem method to determine the equivalent thermal conductivity.Selecting a suitable inverse problem method is a key issue.In this thesis,the foam sphere method and the QSGS algorithm are used to generate the porous medium model,and then the finite element software ABAQUS is used to solve the direct problem of the porous medium,and the problem is simplified as heat conduction.This thesis based on the Levenberg-Marquardt(LM)algorithm and the inverse problem program is constructed to determine the isotropic and anisotropic thermal conductivity of two-dimensional and three-dimensional porous media.The influential factors that affect the accuracy and efficiency of the calculation of the equivalent thermal conductivity are investigated,and the influence of the measurement error on the accuracy of the prediction in engineering applications is also studied.Finally,the fiber-reinforced porous media and random granular porous media are taken as examples to study the factors that affect the accuracy of the algorithm for calculating anisotropic thermal conductivity.The results show that the LM algorithm has good adaptability in calculating the equivalent thermal conductivity of different types of porous media.