Study On Aerodynamic Characteristics And Internal Environment Of Supper Heigh Speed Vacuum Tube Transportation

Improving the speed of train is an important direction of rail transit technology development.Wheel rail train gets a wide use,but it is limited by the wheel-rail friction,aerodynamic drag,and noise.Maglev train adopts magnetic levitation technology to eliminate the wheel-rail friction,but it still cannot solve the problems of aerodynamic drag and noise.The vacuum tube train system combines the technology of vacuum and magnetic levitation,therefore can greatly reduce the aerodynamic drag and noise.It is an important direction of the study on rail transit technology.However,as a maglev train runs at a super-high speed in a closed tube,it will produce a great amount of aerodynamic heat,and the generation of shock waves and choked flow also has a great effect on the environment in the tube and the aerodynamic characteristics of the train.The study on the aerodynamic and internal environmental characteristics of the vacuum tube train system is an important foundation for the design and can ensure the safe and stable operation of the vacuum tube train system,which has great research significance.In this thesis,a numerical model of the vacuum tube train system is established based on an on-building test platform.Through the comparative analysis with a wing experiment,the accuracy of this numerical model is verified.After that,the significance of radiation to the research of the vacuum tube train system is confirmed.Based on the numerical simulation,the basic characteristics of the aerodynamic and internal environment of the vacuum tube train system under the standard working condition are studied,and the variation of aerodynamic drag,shock wave and choked flow,pressure and temperature distribution,and piston wind during each stage are deeply analyzed.It is found that the shock wave and choked flow are generated and is strengthened with the continuous acceleration of the train.In the uniform speed motion stage,a positive shock wave is generated at the front end of the choked flow.In the deceleration section,the intensity of the shock wave and choked flow continues to be weakened and disappears rapidly.The aerodynamic drag of the vacuum tube train continues to increase in the acceleration stage,changes violently under the influence of shock wave,and reaches the maximum value at the end of the acceleration stage.The aerodynamic drag decreases slightly in the uniform speed motion stage.During the initial stage of deceleration stage,the aerodynamic drag decreases continuously,and becomes more rapidly due to the disappearance of shock wave.The distribution of pressure,temperature and wind speed in the tube is greatly affected by the generation and disappearance of shock wave,and its maximum values appear at the end of the uniform speed motion stage.In summary,the aerodynamic and internal environmental characteristics of the vacuum tube train system change greatly with the train operation state,and thus relevant research must be carried out in combination with the train operation state.Finally,through the comparative analysis of the numerical results under different initial ambient temperatures,this thesis studies the influence of the initial ambient temperature on the aerodynamic and internal environmental characteristics of the vacuum tube train.It is found that the change of initial ambient temperature influences the aerodynamic and internal environmental characteristics of the vacuum tube train system by changing the Mach number of air flow around the train.With the increase of ambient temperature,the time point of the generation of shock wave structure in the rear and choked flow in front of the train is delayed,and the variation of pressure,temperature,and piston wind in the pipeline is weakened.