Thermal-mechanical Analysis And Optimization Design Of The Semi-active And Active Thermal Protection Structure Used For Advanced Vehicles

Hypersonic vehicles have become a hot issue in recent years and they are also the tendency of aerospace crafts in the future.During their flying across the atmosphere with high speed or over a long period of time,hypersonic vehicles suffer intense aerodynamic heating load and mechanical load.To make sure the underlying structure not fail,the thermal protection system(TPS)must be used to ensure the temperature and thermal stress within an acceptable limit to protect the fuselage and underlying structure.Design of thermal protection system is one of the key technologies for hypersonic vehicles.Therefore,investigation on several kinds of TPS is conducted which is mainly on analysis of the heat transfer,fluid flow and thermal stress is done in this paper.Firstly,the investigation on the multilayer TPS is conducted.A theoretical model is built combining radiation and conduction heat transfer in high temperature multilayer insulations under aerodynamic heating conditions.After a reliable validation with previous references,the effects of the number,the layout of the foils on the insulation performance of multilayer thermal insulations,the density of the insulation material and the emissivity of the surface of the foils are investigated,respectively.An optimum choice under this condition is obtained.Secondly,the heat pipe applied at the leading edge is investigated.The model composed of four layers,from outside to inside are superalloy,refractory composite,container and the “wall” combined of the wick and the working fluid,are built.It is found that,when the heat pipe is applied at the leading edge,the temperature near the stagnation point and the temperature difference of the structure decreases sharply compared to the structure without heat pipe,which can effectively reduce the stress of the structure.Based on the above,effects of the half wedge angle,the design length and the porosity of the wick on the temperature distribution of the structure are discussed,respectively.Thirdly,the fluid flow and heat transfer of corrugated sandwich actively cooling structure is investigated.A three-dimensional model of corrugated sandwich structure is built,and the coolant is used in the channels to reduce the temperature of the structure,which proves the high effectiveness of the actively thermal protection structure.Based on the structure,effects of the inlet velocity,the flow pattern and the angle between the web and the inner pannel are respectively investigated.At last,thermal-mechanical coupled analysis on the corrugated sandwich actively cooling structure is done.Compared to the corrugated sandwich structure filled with insulation material,the corrugated sandwich actively cooling structure shows great superiority.The temperature at the time when the temperature gradient is the highest is applied on the structure as the temperature load before the structural analysis.It is found that,under combined thermal and structural loads,thermal loads plays a more important role in the total stress,and the stress of the structure is much lower than the allowable value of the structure,so the corrugated sandwich structure has a great potential in optimization.