Analysis Of Aerodynamic Effects Of The Inter-stepwise Buffer Structure In High-speed Railway Tunnel

The initial compression wave will radiate outward in the modality of micro-pressure wave at the outlet of the tunnel,which engendered by the high-speed train entering the tunnel.It will lead to acoustic explosion and affect the surrounding environment.As the speed increases,the aerodynamic problems are gave rise to a train enters the tunnel is becoming increasingly grievous.How to abate the amplitude of micro-pressure wave and retard the aerodynamic effect has become the critical technology of high-speed railway tunnel project.The research shows that the crux of retarding aerodynamic effect is to derate the maximum pressure gradient of initial compression wave.Setting a buffer structure at the portal of the tunnel has always come into effect.However,the speed raising reconstruction of existing lines in Western China is greatly limited by the terrain,it is impossible to set a buffer structure in open line position.Therefore,a new inter-stepwise buffer structure is conceived in this thesis,and the effect on reducing the maximum pressure gradient is analyzed based on numerical simulation.Taking the double-track tunnel and the Fuxing CR400-BF high-speed train as the research object,based on the three-dimensional,compressible and unsteady Navier-Stokes equation and k-εtwo-equation turbulence model,the pressure fluctuation of the initial compression wave engendered by a train entering the tunnel was simulated by using the sliding grid technology.The main contents of this thesis are as follows:（1）The three-dimensional computation model of train-tunnel is established,and the computation model is verified.The pressure curve calculated by the computation model fits well with the test curve,which certificates that the computation model has certain accuracy and feasibility.（2）The wavefront characteristics of compression wave engendered when the high-speed train enters the tunnel with or without inter-stepwise buffer structure are studied in particular.The results show that the setting of inter-stepwise buffer structure can delay pressure rise and effectively reduce the maximum pressure gradient.（3）The influence of train speed change on tunnel aerodynamic effect is explored.The results show that the maximum pressure P_max and maximum pressure gradient （?P/?t）_max of compression wave enlarge with the raise of speed.The reduction effect of inter-stepwise buffer structure on the maximum pressure gradient decreases with the increase of speed,but the reduction effect is between 23%～26.5%,which can effectively retard aerodynamic effect.（4）The reduction effect of inter-stepwise buffer structure with different forms and structural parameters on the maximum pressure gradient is discussed.The research results show that the inter-stepwise buffer structure has no obvious effect on reducing the maximum pressure of initial compression wave,but it can delay the pressure rise and greatly reduce the maximum pressure gradient.When the inter-stepwise buffer structure is located 60m away from the tunnel entrance,the expansion form is three-way uniform expansion,the order is first,the aspect ratio is 16:25,the length is 30m and the cross-sectional area is 150m²,the effect on reducing the maximum pressure gradient is the best,which can up to 24.66%.