Prediction Of The Aerodynamic Heating And The Response Of Thermal Protection Material/Structure In Hypersonic

Hypersonic vehicle has a very important military strategic significance and a wide range of civil prospects,which is an important direction of the aerospace industry.The aerodynamic environment of the hypersonic vehicle is very bad and the influencing factors are complex.There is a strong coupling between hypersonic flow field and material/structure of thermal protection system.Accurate prediction of the hypersonic flow field and the material/structure response is the premise and foundation of the thermal protection system design.During the flight of hypersonic vehicle,the incoming air is compressed by shock wave resulting in a large amount of kinetic energy converted into heat energy,which leads to the high temperature gas effect in the external flow field and serious aerodynamic heating on the surface of the vehicle.On the one hand,the aerodynamic thermal environment causes the ablation of materials and deformation of the structure.On the other hand,the ablation of materials and deformation of structure also affect the external flow field.Aerodynamic thermal environment,which has a serious impact on the use of the thermal protection system of the aircraft,poses a great challenge to the thermal protection materials and structures,and becomes one of the difficulties in the development of hypersonic vehicle.This paper mainly studies the influence factors of hypersonic aerodynamic thermal prediction,the flow field in the gap and its local thermal environment,and the response prediction of the thermal protection material/structure in the aerodynamic thermal environment.The details are as follows.(1)The aerodynamic heating of typical aircraft configuration is studied.The effects of high temperature chemical non-equilibrium,wall catalysis and flight height on the aerodynamic thermal environment are analyzed.The sensitivity of wall catalysis to the prediction of aerodynamic heating is studied.The characteristics of the external flow field and the aerodynamic thermal environment of the typical shape of cylinder blunt head and sphere cone are obtained.The high temperature chemical non-equilibrium changes the aerodynamic thermal environment of the flow field.Using the high temperature chemical non-equilibrium model relative calorimetric complete gas model,the calculated flow field is more consistent with the experimental result.The high temperature chemical non-equilibrium effect reduces the distance of shock wave debonding from 15.1 mm to 11.8mm,the temperature in the shock wave from 9647k to 8287k,and the heat flux on the wall decreases by 24.2%.But it has little influence on aerodynamic force.The wall catalysis accelerates the compound reaction between the chemical components near the wall,and the heat flux increases by 19.8%with the fully catalytic wall compared with the non-catalytic wall.The sensitivity of the catalytic effect to the prediction of aerodynamic heat is obtained under different Mach number,radius of curvature and wall temperature.The aerodynamic thermal environment of the sphere cone model at flight altitude of 71km and 81km is analyzed.With the increase of flight altitude,the chemical reaction rate decreases,the aerodynamic heat becomes stronger and the aerodynamic pressure decreases.(2)The flow field and local thermal environment of the gap in hypersonic environment are studied.The results show that there is a certain vortex motion in the gap,the air velocity in most areas of the gap is low,and the gas near the bottom of the gap is almost static.The heat flux on the wall of the gap presents a U-shaped distribution,and there is a hot spot at the exit of the gap,which is the focus of the thermal protection design.The heat flux in the gap will increase with the increase of the angle of attack and the Mach number,but the vortex structure,the local thermal environment and the distribution of heat flux on the wall are basically consistent.When the gap width is fixed,the change of the gap depth has little influence on the heat flux of the front and rear wall.When the gap depth is fixed,the heat flux of the front and rear wall increases with the increase of the gap width.In addition,the number of the main vortices in the gap is limited by the width depth ratio of the gap.The inflow condition determines the number of the largest main vortices in the gap.The local thermal environment of the gap can be effectively improved by chamfering the exit of the gap.(3)The coupling relation between hypersonic flow field and materials is studied.A multi physical field coupling model of flow-heat-ablation is established,and the coupling model is verified by the ablation test of D6AC in the wind tunnel environment.The heat conduction and ablation of the carbon/carbon composites in hypersonic environment are studied by using flow-heat-ablation multi physical field coupling method.In the initial stage of the front edge model of carbon/carbon composite,the heat flux value in the stagnation region is the largest.As time goes on,the wall temperature of the material increases gradually,the temperature gradient in the stagnation region decreases,the heat flux also decreases,and the wall temperature and heat flux change significantly with the passage of time.At 30 s,the ablation depth of the stagnation point is 17.5mm,while only a small amount of ablation occurs on the side of the model,and the radius of the front edge of the model increases.(4)The thermal response of nose cone structure in hypersonic environment is studied,and the shape of nose cone is optimized.Taking the nose cone structure of the Italian Aerospace Research Center as the research object,the two-way multi physical field coupling model of nose cone is established,and the variation law of the internal temperature and the maximum principal stress distribution of the structure with the flight time is obtained.In the initial stage,the maximum temperature and the maximum principal stress of the nose cone structure appear at the nose cone head.With the passage of flight time,the maximum temperature gradually increases,and finally tends to be stable.After the maximum principal stress reaches a certain value,it gradually decreases,and the position of the maximum principal stress gradually moves towards the inside of the nose cone,and finally tends to be stable.With the increase of Mach number,the heat flux on the wall increases gradually,and the temperature and the maximum principal stress of the nose cone structure increase.Genetic algorithm is used to optimize the shape of nose cone structure.Based on the objectives of mass,aerodynamic force and aerodynamic heat,the results of multi-objective optimization are RN=0.04m,?c=14°,Rb=0.019m.In this paper,through the interdisciplinary and integration of hypersonic aerodynamics,heat transfer,structural mechanics,materials science and chemistry,some achievements have been made in the prediction of the aerodynamic thermal environment,as well as the response of the thermal material/structure in the aerodynamic thermal environment,which can provide some references for the design and optimization of thermal protection system of hypersonic vehicle.