Design And Heat Transfer Analysis Of The Thermal Protection Structure For Electric Linear Actuator In Cryogenic Wind Tunnel

With the speedy development of aerospace technology,wind tunnel test ha s become an indispensable method to simulate the space flight of aircraft on the ground.Conventional wind tunnels cannot simulate the operation condition of aircraft in full-size Re because of the limitation of various factors such as structures and powerplants,which makes distortions and even mistakes of the results,and causes inestimable losses.In order to increase the Re of wind tunnels and make it approach to or reach the actual operation value of the aircraft,lowering the operating temperature of wind tunnels is a common method.The interior of cryogenic wind tunnels can reach cryogenic state during its normal operation.If components in the cryogenic wind tunnel are directly exposed to cryogenic environment,they will not work normally and even be damaged.In order to ensure normal operation of the components in the cryogenic wind tunnel,a thermal protection structure for the electric linear actuator working in the cryogenic wind tunnel was designed.Based on numerical simulation software,the strength and heat transfer of the designed thermal protection structure were analyzed.The main work is as follows:(1)The thermal protection structure for electric linear actuator in the cryogenic wind tunnel was designed.Based on the operating environment and technical indicators of thermal protection in cryogenic wind tunnel,thermal protection structures of polyurethane foam and vacuum insulation were designed.By comparison,the thermal protection structure of polyurethane foam was selected.In view of heating of the motor and local low temperature of the electric linear actuator under cryogenic condition,gas cooling system and local heating element are provided to meet the functional requirements of the thermal protection structure.(2)Analyses of nonlinear buckling and strength for the thermal protection structure were completed.Considering nonlinearity of the material and the initial geometric imperfections of the structure,the finite element model of buckling analysis for the thermal protection structure was established and analyzed with ANSYS software.The maximum buckling position of the structure was determined,the relationship between the size and form of the initial geometric imperfections and critical pressure of the structure was obtained,and the stress intensity of the structure was also calculated.The results show that the designed thermal protection structure can meet the requirements of stability and strength.(3)The heat transfer of the thermal protection structure was analyzed.A numerical calculation model of heat transfer for the thermal protection structure was established,and the analysis of heat transfer was performed.Influence rules of flow rate of cooling gas,positions of inlet and outlet,power of heating element,and thickness of the polyurethane foam insulation layer on the temperature distribution of the electric linear actuator were obtained.Reasonable process parameters were determined after optimization.It is revealed that the cylinder and cylinder rod of the electric linear actuator can be maintained within the temperature range of 263K-313 K,and meets the requirements of temperature stability and uniformity.