Research On Coupled Heat Transfer Method And Thermal Response Characteristics Of Heat-pipe-cooled Thermal Protection Structure

As the development of hypersonic vehicles, the design of thermal protectionsystem to keep the high lift-to-drag aerodynamic configuration and ensure the thermalstructural safety during sustained severe aerodynamic heating, particularly at wingleading edge, has been one of the critical skill shortfalls. In recent years, the design ofheat-pipe-cooled leading edge thermal protection structure (HPCLE TPS) has becomeone of the effective means to break through the above technical bottleneck, and thestudies have drawn wide attention from the research field. However, for the complexitycomparing to conventional thermal protection structures, there are still some difficultiesin the engineering application of HPCLE TPS. Because of the lack of analyticalapproach for complex multiphase heat transfer, the thermal protective mechanisms andtheir effects are not known sufficiently. In order to overcome the above problems, theheat transfer properties of the typical HPCLE TPS with the vapor-phase, solid-phaseand liquid-phase coexistence inside are studied, and the numerical solving method ofthe three-dimensional thermal response with multiphase is proposed in this paper. Usingthis method, the thermal protective performance is analyzed, and the mainly influencefactors and their effects are discussed.Firstly, the theories of heat transfer, thermodynamics and fluid dynamics are usedto develop the coupled heat transfer analytical approach, for complex heat transfermechanisms of the structure including surface radiation, internal heat conduction,convection and phase-change heat transfer. In order to simulate the coupled heatconduction and melt process, the model of variational melting coefficient based on theassumption of linear stepwise latent heat release is proposed. Based on the studies byCotter, a homogenization boundary treatment with the weight coefficient of temperatureis used to simulate the coupled heat conduction and evaporation/condensation process.Besides, a method based on both the Maxwell theory about molecular average free pathand the approach of flat-front trace is proposed to analysies the transient process fromrarefied to continuum flow. Furthermore, a modified method considering the influenceof the heat transfer limits of heat pipe is developed. Then, with space discretizing by finite volume method and time processing byRunge-Kutta-Fehlberg method, the completely method of thermal response is proposed,and the codes are developed. Using the codes, the thermal response characteristics ofHPCLE TPS are studied. As a result, not only the effects of stagnation heat flux, surfaceemissivity, carbon-carbon material thickness, heat-pipe inside diameter, heat-pipelength and spacing are obtained, but also the improvements of spanwise heat-pipes andinternal active cooling are discussed.Overall, the simulation approach for the thermal response of HPCLE TPS isdeveloped in this paper, which can be used to analysies the whole process fromheat-pipe forzen startup state to steady state. Meanwhile, the effects of influence factorsare obtained with the systematic studies of thermal protective performance. On the onehand, the research results can provide the theoretical basis and technical supports for thedesign, optimization and performance evaluation of HPCLE TPS. On the other hand,the model and numerical method of coupled heat transfer can provide importantreferences for the research on multiphase heat transfer problems.