Visualization of unsteady flow generated by a train entering a tunnel

The impulsive pressure wave radiated from a tunnel exit (micro-pressure wave) is one of the most important environmental problems of high-speed railways. For solving the problems of micro-pressure waves, the unsteady flow induced by a train entering a tunnel needs to be clarified because the micro-pressure wave is radiated at the arrival of the compression wave generated by the train entry. In this study, we conduct a 1/127 scale model experiment and investigate the unsteady flow induced by the train entering the tunnel by applying the flow visualization technique to use oil mist and a high-speed camera. The results reveal that a jet flow is emitted from the entrance and a vortex ring is generated and collapses thereafter. Furthermore, a jet flow from a window at the tunnel side wall is also observed.