Numerical Study On Aerodynamic Heating Of Thermal Structural Materials For Hypersonic Vehicle

Hypersonic vehicle with a flight speed above Mach5is the forefront ofcurrent research in the field of aerospace. One of the key technologies is theaerodynamic thermal protection problem of hypersonic vehicle. When a vehicleflying at a high speed in the atmosphere, due to the viscous effect between thebody and the air, the body surface boundary layer of air is strongly compressedand influenced by frictional force, then the gas energy and temperature increasegreatly. It is extremely important to research inherent mechanism of aerodynamicheating and enhance the thermal protection technology for protecting thehypersonic vehicle from damage and internal functions being not affected.For decades of development, research of hypersonic aerodynamic heatinghas achieved initial results, and got the distribution of the flow characteristicsand structural properties, and laid a theoretical foundation. With the gradualdeepening of the study, more problems come out, such as the transitionphenomena of hypersonic boundary layer and the complex hypersonicflow-heat-solid coupling course. In this thesis, some related simulations will becarried out to solve above problems.Firstly, a numerical study on hypersonic aerodynamic heating of externalflow field around typical models is carried out. The results are compared withexperimental data to compare the suitability of different turbulence models in thecalculation of hypersonic aerodynamic heating. And on this basis, the effects ofdifferent Mach numbers, different angles of attack, different wall temperaturesand different stream turbulence intensities on the simulation results are studied.Secondly the flow-heat-solid coupling simulation of hypersonic vehicle isinvestigated. Two coupling methods, Two-Way coupling and One-Way coupling,are applied to research and analyze flow-heat-solid coupling field of the cone ofthe vehicle. And on this basis, an optimal design of structural materials is carriedout to enhance the aerodynamic resistance to thermal shock.From the result of numerical study on hypersonic aerodynamic heating ofexternal flow field using typical models, it’s shown that in the external flow field, when boundary layer transition is ignored, the result using SST k-ω model issuperior to that using the standard k-model and using the standard k-ω model inthe three two-equation turbulence models. Also, hypersonic aerodynamic heatingof the external flow field can be accurately simulated using SST k-ω model. Also,considering boundary layer transition under different Mach numbers anddifferent angles of attack, it cannot predict the boundary layer transition usingthe one-equation turbulence model and two-equation turbulence model, while itcan accurately predict the occurrence of boundary layer transition and analysisthe transition effects on the heat transfer using a three-equation turbulence modelnamed Transition k-kl-ω model. Wall heat flux and free stream turbulenceintensity affect the position of the boundary layer transition, but the Machnumber only affects the post-transition heat flux values. The quality of the meshand the mesh density on the key parts largely determine the simulation accuracy.When calculating the hypersonic flow, y+value of the grid at the wall should beless than1.From the result of numerical study on the flow-heat-solid couplingsimulation of hypersonic vehicle it’s shown that two-way coupling method canaccurately simulate flow-heat-solid coupling simulation. The result usingOne-way coupling method shows the top node temperature is higher, and the topof the cone has a larger temperature gradient and thermal deformation gradient,while high temperature and deformation zones are concentrated in the top area.Two-way coupling method can solve the above problems. Temperature gradientis relatively low, and the wall heat flux of the high temperature area declines; thethermal deformation gradient of the structure caused by temperature changes isless, and the thermal stress is lower. The calculated wall temperature by two-waycoupling method will gradually rise over time, and the increasing rate graduallydecreases, and the wall temperature distribution is positively correlated with thedistribution of wall heat flux. Compared with30CrMnSiA alloy and Nb alloycone, the temperature of the cone using C/SiC composite is the highest, but thethermal deformation is the lowest. And the temperature is within the scope ofC/SiC composites. The C/SiC composite not only has the ability of resisting tothermal shock, but also the ability insulating heat. Therefore C/SiC compositescone enhances the aerodynamic resistance to thermal shock.