Model experiment and analysis of pressure waves emitted from portals of a tunnel with a branch

A model experiment was performed to investigate pressure waves generated by a train passing by a branch and pulse waves radiated from portals of a main tunnel and the branch. For the experiment, the train speed was set as 400–500 km/h. The cross-sectional area ratio of the branch to the main tunnel was 0–0.5. The cross-sectional area ratio of the branch to the main tunnel was identified as a dominant factor in determining the magnitude of the pressure waves in the tunnel and the pulse waves radiated from the portals. Closed form expressions for the magnitude of the pressure changes generated by a train passing by a branch were derived using low Mach number approximation. Correlation between the pressure waves in the tunnel and the pulse waves radiated from the portals was clarified using simple acoustic theory. The overall tendency of the experimental results is explainable based on analytical results.