The Experiment And Numerical Simulation On The Pressure Produced By A High-Speed Train Entering Into A Tunnel

The train entry into a tunnel generates an exiting flow at the portal with a direction opposite to the train movement and a compression wave that propagates into the tunnel at the speed of sound. Developments of high-speed trains have generated numerous engineering problems related to the presence of strong compression waves in tunnels. The high amplitude of compression waves provokes strong mechanical stresses on the train body and the associated high pressure gradients are responsible for both the aural discomfort of train passengers and the impulsive acoustical wave called the micro-pressure wave emitted in the surrounding area of tunnel exits. The micro-pressure wave is similar to the aeronautical sonic boom and caused serious environmental damages.To discover this problem, the paper relies on the item of the national natural science fund undertaken by Southwest Jiaotong University for the experimental studying on the aerodynamic feature of tunnel-hood, according to the field features induced by a high-speed train entering into tunnels with or without hood to establish three-dimensional unsteady viscous compressible isentropic flow to model compression wave.The experiment and calculation show that the compression wave which propagates along the tunnel at the speed of sound is formed when the train enters into the tunnel. The pressure amplitude of the compression wave creases to the positive maximum at the time the train nose just enters into the tunnel entrance while the negative pressure amplitude is formed when the train tail just passes by the measurement points. The train speed and the train/tunnel ratio are the main factors which influence the pressure amplitude and the pressure gradient of the compression wave, and draws that the maximum amplitude of the fully established compression wave is approximately proportional to the square of the train speed, the maxim- um of the pressure gradient is approximately proportional to the cube of the train speed. For a given train section area, the larger the tunnel section is, the weaker the compression wave amplitude and gradient are. It is also related to the train passing through the single or dual tracks tunnel.The calculation show that there are horizontal and vertical fluctuation for the wind induced by the train passing through tunnel, and the field of velocity is verycomplex, so it has the feature of unsteady fluid. At the same time, there is phenomenon of the annulus jet accompanied by a vortex ring when the train enters into the tunnel. The formation of the vortex ring constitutes four phases, the pre-vortex phase, the vortex development phase, the vortex convection phase and the vortex breakdown phase. The duration of each of these steps is found to be independent of both the studies parameters. Furthermore, neither the train speed nor the train nose geometry induced significant changes on the vortex ring evolution.The various shapes of train can decrease effectively the maximum pressure gradient because of modifying the generation process of the compression wave. The calculation releases that the maximum pressure gradient of the compression wave in the case of triangle of revolution is the smallest of the five fundamental nose shapes: a triangle of revolution, a quardrilateral of revolution, an ellipsoid of revolution, a paraboloid of revolution, and a circular cone. Then in the case of paraboloid of revolution, and the quardrilateral of revolution is biggest. At the same time ,the more the length of nose is ,the more the maximum pressure gradient is.The maximum pressure gradient of compression wave front increases during propagation in duct sections of constant cross-section in slab track tunnels and decreases at branched sections. The effective of the branch for reducing the maximum pressure gradient depends on the branch length, the branch cross-section area and the position of the branch from tunnel entrance.The change of the shaft cross-section area and the position from the tunnel entrance can decrease the maximum pressure amplitude and...