Study On The Coupling Effect Of Temperature And Pressure Of High-temperature Superconducting Pinning Maglev System In Low-vacuum Tube

Raising speed has always been the eternal theme of the development of rail transit.Vigorously developing the new ultra-high-speed rail transit is not only a requirement for the economic development and social progress,but also an inevitable requirement for our country to occupy the commanding heights of rail transit technology and lead the direction of future rail transit development.However,the speed improvement space of current wheel-rail train is limited by the hunting instability,the limiting speed of pantograph-catenary and adhesion coefficient.The maglev train has no contact with the rail,avoiding wheel-rail adhesion and eliminating wheel-rail noise,but the problems such as aerodynamic drag,aerodynamic noise,and aerodynamic heat are still need to be resolved in the atmospheric environment.The low-vacuum tube can reduce the density of the air in the tube,thereby improving the aerodynamic characteristics of the train.Therefore,the combination of low-vacuum tube and maglev train is expected to achieve a super-high-speed operation on the ground,which has a certain prospect of engineering application.It is impossible to achieve a complete vacuum inside the tube,the air flow inside the low vacuum-tube will still interact with the train and the tube,resulting in the change in the temperature and pressure on the surface of the train and tube.In this thesis,combined with the levitation characteristics of the recently launched high-temperature superconducting（HTS）pinning maglev engineering sample vehicle,the distribution characteristics of temperature and pressure in the HTS pinning maglev transportation system in the low-vacuum tube are studied based on the STAR-CCM+fluid simulation software.Firstly,based on the turbulence model of the three-dimensional,steady and compressible Reynolds average N-S equation and SST k-ωequation,the three-dimensional simulation models of low-vacuum tube and HTS pinning maglev engineering sample train are established.Then STAR-CCM+fluid simulation software is used to generate volume grids in the computational domain,and the grid independence and numerical method are verified.The results show that:the size of the volume mesh adopted in this thesis can ensure the accuracy of the simulation,and the pressure coefficient calculated by the ONERA-M6 airfoil is in good agreement with the wind tunnel test data,which indirectly shows that the numerical method selected in this thesis is reasonable.Secondly,the air flow state of the HTS pinning maglev train running in the tube under multi-factor working conditions is simulated by STAR-CCM+software.Through numerical simulation,the effects of different speeds V_train（400 km/h,600 km/h,800 km/h,1000 km/h,1200 km/h）,different initial air pressures P（0.01 atm,0.02 atm,0.05 atm,0.1 atm,0.2 atm）in the tube and different blockage ratiosβ（0.20,0.24,0.33,0.44）on the aerodynamic resistance of the train and the thermal pressure distribution on the surface of the dewar were investigated.Finally,the problem how the temperature field and pressure field change when the HTS maglev train runs in the tube at a transonic speed is analyzed in this thesis,then the influence of different speeds,different initial pressures and different blockage ratios on the thermal pressure distribution of the air flow on the surface of the tube is further explored.Combined with the vertical profile of pressure field and temperature field in the tube,the distribution characteristics of temperature and pressure and influence law of flow field in the tube are further explored.The results show that the shock wave will appear in the wake area at high speed,which leads to the sudden rise of pressure and temperature in the tube and flow field near the tail car.In the meanwhile,the train speed will affect the length of the shock zone;the initial pressure in the tube will affect the pressure fluctuation when the air flows through the shock wave.