Theoretical study on the most unfavorable tunnel length (MUTL) based on the interior pressure variations of high-speed subway trains

Abstract

When a high-speed subway passes through a tunnel, the external aerodynamic pressure of the train is transmitted into the train interior, which adversely affects the passenger comfort. The effect of tunnel length on the interior pressure variation of the train cannot be ignored. According to previous studies, there is a most unfavorable tunnel length (abbreviated as MUTL in this paper) for the exterior pressure of the train. However, MUTL for the interior pressure variation is still a research gap. In this study, the effect of tunnel length on the interior pressure variation of tunnel and train was investigated using numerical simulation and TWS method. Additionally, the theoretical formula of MUTL based on the internal pressure variation at the head and tail of the train was established and verified using the results of past field measurements and TWS method. The findings indicate that the interior pressure variation with tunnel lengths within a certain time interval is not monotonic. Moreover, there may be two or even more MUTLs, and the MUTL is also be influenced by the dynamic sealing index. MUTL decreases with increasing train speed and increases with increasing number of cars. The research findings of this paper address the research gap in the study of MUTL on the pressure variation inside trains. These findings offer new theoretical guidance for the research of aerodynamic effects in high-speed subway tunnels, and provide a valuable reference engineering design and optimization.