Nature of pressure waves induced by a high-speed train travelling through a tunnel

The pressure waves generated by a train entering and running through a tunnel are studied experimentally and numerically with the aim of gaining a solid understanding of the flow in the standard tunnel geometry and in the configuration with airshafts along the tunnel surface. Laboratory experiments were conducted in a scaled facility where train models travelled at a maximum velocity of about 150 km/h through a 6-m-long tunnel. The flow was simulated by a one-dimensional numerical code modified to include the effect of the separation bubble forming near the train head. The numerical simulations reproduced well the experimental results. We tested the influence of the train cross-sectional shape and length on the compression wave produced by the vehicle entering the confined area. The cross-sectional shape was not found to be influential as long as the blockage ratio, namely the ratio between the train and tunnel cross-sectional areas, is constant. The pressure waves are one-dimensional sufficiently downwind of the tunnel mouth, which validates the comparison between the experimental and computational results. It is further shown that the numerical code can satisfactorily reproduce the pressure variations for the case with airshaft apertures along the tunnel surface.