Study On Aerodynamic Effects Of High-speed Train Tunnel

The tunnel line plays an important role in the running of high-speed trains.Although the tunnel reduces the distance of railway lines,the accompanying aerodynamic problems are particularly prominent.The tunnel has various forms,and the transient pressure,piston wind,aerodynamic resistance and other problems in the tunnel have a direct impact on train safety and passenger comfort.In this paper,based on the three-dimensional,unsteady and compressible Reynolds time mean N-S equation and k-ε turbulence model,the numerical simulation results of aerodynamic effects of high-speed trains passing through the tunnel are studied by using the finite volume method using the sliding grid technique in Star CCM+fluid dynamics software.The main research work of this paper is as follows:(1)The computational aerodynamics model of train passing through the tunnel is established by using Hyper Mesh software.Based on the geometric model of 3-train grouping of CRH3 EMU,the surface grids of train surface and computational domain are divided.Star CCM+ computational fluid dynamics software was used to discretized the flow field in the model by using the combination of structured and unstructured grids,including the boundary layer on the train surface and the mesh encrypted area near the train.(2)The flow field characteristics of the train passing through 150 m tunnel at 300km/h were calculated and analyzed.In the process of train entry and departure,the velocity field,pressure field,pressure value of measuring point and the calculation results of microbarometric wave at the exit are analyzed.The analysis results show that there are airflow separation and vortex in the area where the curvature of the head and the vehicle shape change greatly.The pressure distribution along the direction of vehicle length on the open line outside the tunnel exit and entrance has obvious partition.Compression and expansion waves travel at the speed of sound in the tunnel.The microbarometric wave at the exit conforms to the relevant national standards.(3)The characteristics of the train surface flow field when the train passes the 300 m tunnel at 350km/h are calculated and analyzed,and the pressure distribution of the train surface and the pressure change of typical measuring points such as the nose tip of the train are obtained.The data were analyzed by extracting the extreme value of each pressure curve.The analysis results show that the maximum positive pressure on the train surface is concentrated at the tip of the nose,and there is a large pressure gradient at the position where the surface curvature changes greatly.The decrease of surface pressure is mainly caused by the expansion wave in the tunnel and the negative pressure effect around the vehicle.(4)The aerodynamic characteristics of trains passing through 150 m tunnel and 300 m tunnel at speeds of 300km/h,350km/h and 400km/h are compared and analyzed.The influence of train speed on the pressure fluctuation effect and the train surface pressure in the tunnel under six working conditions is calculated and analyzed.And the influence of tunnel length on the pressure wave propagation process and train surface pressure.The calculation results show that the train speed is positively correlated with the pressure inside the tunnel and the amplitude of microbarometric wave at the exit.The maximum pressure at each location depends on the surface position and running speed of the train.As the tunnel length increases,the position where the maximum positive pressure value appears on the inner wall of the tunnel moves towards the exit.The distribution of extreme pressure on the train surface is related to the time the train travels in the tunnel.