Aerodynamic Characteristics of City Railway Train at the Sudden Variable Tunnel Cross-Section Positions

［Objective］In order to ensure train operation safety and passenger comfort, it is necessary to study the chang-ing laws of aerodynamic force and pressure inside the city railway train when passing through the variable cross-section positions in the tunnel (entering the platform, running in the tunnel, and passing through the intermediate air shaft). ［Method］Taking the 8-carriage city railway train as an example, a numerical calculation model is established. A numerical simulation study on the aerodynamic performance at the variable tunnel cross-section is carried out, and the changes in the train body surface pressure, tunnel wall pressure, train aerodynamic force, and pressure inside the train are analyzed respectively. ［Result & Conclusion］The changing laws of train body surface pressure and aerodynamic load are as follows: the surface pressure and lateral force with train entering the station > the surface pressure and lateral force with train passing through the intermediate air shaft > the surface pressure and lateral force when the train runs into the tunnel. The train body surface pressure amplitude is linearly related to the 1.4 ~ 2.0 power of the train running speed; the tunnel wall pressure is linearly related to the 1.79 ~ 2.10 power of the train running speed; the train body lateral force is linearly related to the 1.8 ~ 2.0 power of the train running speed, and the overturning moment is linearly related to the 1.6 ~ 2.0 power of the train running speed. The air-tightness design of the city railway train can meet the human comfort standard requirements, namely the pressure change inside the car at the variable tunnel cross-section positions shall not exceed 800 Pa per 3 seconds and 500 Pa per 1 second.