Objective  When a high-speed train passes through high-altitude steep-grade tunnels or meets other trains inside the tunnels, significant aerodynamic phenomena can be possibly induced, leading to intense fluctuations in the external pressure of the trains. When the transient pressure transmits into the passenger cabins, it will cause ear discomfort and medical safety and health problems for crew and passengers. Therefore, further research is needed to explore how to reduce or mitigate the impact of external pressure changes on the internal pressure fluctuations under continuous high-altitude steep-grade tunnel operating conditions.

Method Taking the characteristics of the Beijing-Zhangjiakou High-Speed Railway tunnels as an example, tests and analyses are conducted on the train cabin internal pressure fluctuations under tunnel operational conditions. Based on theoretical knowledge and on-site measured data, optimizations are made to the opening-closing valves and forced valve-opening logic of the passive pressure protection system. Additionally, a pressure relief mode is added to reduce the interior and exterior pressure difference of the train.

Result & Conclusion During operation on lines with significant altitude variations and substantial atmospheric pressure differences, the external pressure continuously penetrates the train interior through the car body, causing passengers to experience persistent ear pressure sensations. During the pressure protection process, if the train's pressure wave relief valve opens abruptly under a large internal-external pressure difference, the rapid influx of external pressure into the cabin may result in brief tinnitus among passengers. When the altitude descends, the rate of pressure fluctuation inside the train is generally higher during open-track operation compared to operation within tunnels.