Characterizing a device for easy simulation of compression waves induced by trains passing through tunnels

When a high-speed train enters a tunnel, an initial compression wave (ICW) is generated, which radiates out as it propagates lengthways through the tunnel to the exit, forming an uncomfortable micro-pressure wave (MPW). The aim of this research is to develop a scaled device to quickly simulate this aerodynamic phenomenon. Our device achieves this by using the instantaneous release of high-pressure air in the chamber. In the first part of the paper, the reliability of this device is verified by various methods, including an airtightness check, calibration of transducers, and repeatability experiments. Next, the mapping of the parameters of the device to engineering values is discussed. The propagation process of the ICW and the pressure fluctuations in the tunnel are then analyzed, and the discussion centers around a control variable case. Finally, the MPW generated near the tunnel exit is explored and acoustically evaluated. It is found that the initial pressure in the chamber, the opening voltage, and the number of solenoid valves in the experiment can be mapped to the train speed, the characteristic length of train nose, and the blockage ratio, respectively. When the pressure amplitude of the ICW is higher, there will be a certain steepening phenomenon in the propagation process. The pressure fluctuation cycle in the tunnel is calculated as 4x tunnel length/wave velocity, and the amplitude of fluctuation decays exponentially over the cycles. In most cases, the sound pressure level of MPWs near the tunnel exit exceeds the hearing threshold, based on the auditory properties of the human ear.