Effect of the shape of the openings in the tunnel entrance hood on the flow around the train

When high-speed trains enter a tunnel, micro-pressure waves are generated at the tunnel exit. The micro-pressure waves cause noise and vibration, which have negative impacts on the surrounding environment. Tunnel entrance hoods are installed at the entrance of the tunnel as a countermeasure against the micro-pressure waves, and some have openings in the side wall. The effectiveness of the openings has been clarified through experiments and acoustic analysis, but the relationship between the openings and flow structure is unclear. In this study, the effect of side-wall openings on the flow around a train was investigated. An experimental system was constructed in which a train model entered a platform model underwater. The flow field was then measured using Particle Image Velocimetry (PIV). The results showed that the presence of openings reduced the velocity component in the direction of travel in front of the train. Furthermore, a comparison was made between a wall with a single central opening and a wall with two divided openings. The results showed that the two-opening configuration suppressed the velocity component over a wider region. These findings indicate that the position and shape of openings influence the flow around the train.