Comprehensive Investigations On Thermal Protection System Of Hypersonic Vehicles

With the development of the aerospace technology,in order to meet the needs of the military and civil,the flight Mach number of the vehicle is getting higher and higher,and the hypersonic vehicle is the hot topic in recent years.China has also developed various types of hypersonic vehicles.All of them met the difficulty of thermal design.The problem of heat protection comes from the aerodynamic heating effect of hypersonic vehicles.In order to ensure the inner structural temperature within the sustainable temperature range,the thermal protection system(TPS)should be designed on the outer surface of the hypersonic vehicle.As one of the key technologies and difficulties of the hypersonic vehicle,the thermal protection performance and integrity of TPS directly determine the safety of the hypersonic vehicle.Therefore,the studies on the thermal protection and integrity of TPS have very important engineering value,which is of great significance to the development of hypersonic vehicles in China.The tile is the most widely used heat insulation structure in the hypersonic vehicle,which is the typical passive TPS.The tile achieves the thermal protection by designing the thickness of the tile and the thermal emissivity of the outer coating under the known external aerodynamic thermal load.For the tile,the main research work in this paper is as follows:Considering the coupling effect between the aerodynamic heating and structural heat transfer,the CFD/NHT division coordinating coupling marching model for the overall thermal control performance of TPS in the nose cone is established.The data exchanges of the wall heat flux and wall temperature are conducted by the bidirectional mapping interpolation method based on the control plane on the coupling surface.The computational accuracy of the division coordinating coupling marching method and the data exchanges are verified by the wind tunnel test model of NASA hypersonic circular tube.The thermal control performance of TPS in the nose cone of the aerospace plane is studied.The results calculated by the uncoupled and coupled method are compared,and the coupling effect is analyzed quantitatively.Finally,the influences of the flight Mach number,the thickness and thermal conductivity of the tile,the thermal emissivity of the coating on the thermal control performance of TPS in the nose cone are studied.For the local thermal control problems of the gap and damaged area in TPS,the CFD numerical method is adopted to study the heat flux distributions in the windward gap and damaged area of the hypersonic vehicle,which are compared with the flat heat flux.The local thermal control performance of TPS is studied by the heat flux in the windward gap and damaged area.The results reveal the cause of the thermal short circuit of the gap and identify the danger part of the damaged TPS.In order to guide the engineering design,the influences of the gap width,the gap fillet and the gap step on the local thermal control performance are studied.In order to evaluate the safety of the next flight,the damage tolerance analysis of TPS is conducted,the maximum allowable damaged width is obtained,and the concept of"damage tolerance curve"for thermal control analysis of TPS is proposed.The flatwise tension,flatwise compression and flatwise shear experiments are conducted to study the high temperature mechanical properties of the strain-isolation-pad(SIP)under the room temperature and high temperature(300?)environments.The fracture surface and failure mode of the specimens are obtained under the different thicknesses of the specimen,the different temperature environments and different load types.In addition,the elastic modulus,the failure stress and failure strain of SIP are obtained,and the influences of the high temperature on the stiffness and strength of SIP are studied quantitatively.Finally,the applicability of the maximum stress criterion and maximum strain criterion to the failure of SIP is studied.The two degree-of-freedom linear random dynamic theoretical model is proposed under the acoustic excitation and acceleration base excitation.The tile and SIP are both considered as the elastic body and simplified as the mass point,the linear spring and the damping element.The linear dynamic theoretical solutions are derived,and the validity of the linear dynamic model is verified by comparing the theoretical results with the finite element numerical results.In order to guide the engineering design,the influences of the structural damping coefficient of TPS system,the elastic modulus and thickness of SIP on the accelerations of the tile and SIP and dynamic stress of SIP are studied.Considering the nonlinear stiffness of SIP,SIP is simplified as the nonlinear spring,and the two degree-of-freedom nonlinear random dynamic theoretical model is proposed.The solving process of the nonlinear theoretical model and the iterative process of the equivalent linear stiffness coefficient of SIP are derived by the statistical linearization method.The influences of the nonlinear stiffness level of SIP and external load on the equivalent linear stiffness coefficient of SIP and nonlinear random dynamic characteristics of TPS are studied.The work in this part provides the theoretical basis and analysis means for the linear and nonlinear random dynamic characteristics of TPS,especially the nonlinear dynamic strength analysis of SIP,which is of great significance for accurately analyzing the dynamic strength of SIP and ensuring the safety of TPS.The flight Mach number of modern hypersonic vehicle increases rapidly,and the wall heat flux rises sharply.The thickness of the tile must increase to ensure the thermal protection performance,which will result in the overweight of the tile.In addition,the maximum temperature of the tile is likely to exceed the limit temperature allowed by the material,which will result in the failure of the tile TPS.Active TPS based on the flow control can directly reduce the aerodynamic heating and wall heat flux.For the active TPS based on the flow control,the main research work in this paper is as follows:The influences of the shape of the front end of the spike and opposing jet on the flow characteristics,the aerodynamic heating of the blunt body and structural temperature field are studied.The thermal protection performances of the spike TPS,the opposing jet TPS and tile TPS are compared,and the excellent thermal protection performances of the spike TPS and opposing jet TPS are verified,which can solve the disadvantages of the overweight of the tile TPS and maximum temperature of the tile exceeding the limit temperature of the material at high Mach number.Influences of the length of the spike and diameter of the aerodisk on thermal protection performance of the spike TPS,and influences of the total pressure and diameter of the jet on the jet mode,the flow characteristics and thermal protection performance are studied.For the spike TPS,the reduction of the aerodynamic heating,the increase of the mass and the reduction of the structural stiffness and strength caused by the increase of length of the spike should be comprehensively evaluated to select the appropriate length of the spike.For the opposing jet TPS,the thermal protection performance,the jet mass and drag should be comprehensively evaluated to select the appropriate size and total pressure ratio of the jet.A new combined non-ablative active thermal protection system(CNA-TPS)is proposed,which consists of the blunt body,the spike,the front and rear jets.CNA-TPS combines the advantages of the spike TPS and opposing jet TPS,and it overcomes the disadvantages of the ablative property of spike TPS and opposing jet TPS pushing the bow shock wave close to the blunt body.The excellent thermal protection and drag reduction performances and non-ablative property of CNA-TPS are verified by the analysis examples.The influences of length of the spike,the sizes and total pressure ratios of the jets on thermal protection and drag reduction performances of CNA-TPS are analyzed.Finally,the sensitivity analysis of the sizes and total pressure ratios of the front and rear nozzles to the total mass flow of the jets m and the total heat flux of the blunt body Q_t is conducted,and the weighting method based on MIGA and NSGA-?method based on the Pareto principle are adopted to conduct the multi-objective design optimization of CNA-TPS on m and Q_t.