Full-scale experimental study on tunnel pressure waves caused by an urban train with various air-intake statuses of air-conditioning units

Urban railways alleviate traffic congestion and enhance transportation efficiency. The operation of trains in tunnels can cause significant pressure waves, resulting in passenger discomfort and auditory damage. Therefore, airtight train configurations were employed to mitigate interior pressure fluctuation. To ensure interior air quality, controlled ventilation through air-conditioning units (ACUs) is required. However, during tunnel operations, pressure waves enter the carriage through ACUs, thereby affecting the interior pressure. Considering that the on-off plates of air intakes may malfunction, the influence of tunnel pressure waves on the auditory comfort of passengers is worth investigating. In this study, a full-scale test was conducted to investigate the spatiotemporal distribution characteristics of the interior/exterior pressure variation induced by trains with different lengths passing through tunnels at multiple speeds. The ACU air intake operates in three states: automatic control (closed), 1/4 open, and fully open. An inverse correlation was observed between train length and interior/exterior pressure variation. Compared with the driver's cab, the interior pressure of the passenger compartments was more affected by the train length (with a difference of approximately 30%). The operational state of ACU air intakes significantly impacts interior pressure variations, with closed intakes effectively reducing fluctuations, whereas opening size demonstrated limited influence. Both the amplitude and variation of the interior/exterior pressure exhibited positive correlations with train speed. These findings inform optimized ACU intake control strategies for enhancing passenger auditory comfort.