Field measurements of the effects of tunnel parameters on aerodynamic pressure and longitudinal airflow velocity inside a metro express train

Increasing the design speed of metro express lines leads to intensified airflow velocity and pressure fluctuations within carriages, thereby compromising passenger ride comfort. In this study, field measurements were conducted on an express metro line with a design speed of 120 km/h. The formation mechanisms and spatiotemporal characteristics of longitudinal airflow velocity and transient pressure variations within the carriage were investigated, and the effects of tunnel length and blockage ratio on these aerodynamic parameters were evaluated. The results show that aerodynamic effects are the dominant mechanism governing the formation of longitudinal airflow during train operation in tunnels. Under these conditions, the longitudinal airflow velocity exhibits a positive correlation with the exterior–interior pressure difference. During the stable flow stage, the maximum average longitudinal airflow velocity reaches 4.27 m/s. For short tunnels, the relatively low energy dissipation of pressure waves during propagation results in larger pressure amplitudes on train surfaces. In contrast, their effect on the average longitudinal airflow velocity remains insignificant. Furthermore, reducing the blockage ratio can substantially alleviate aerodynamic effects. Specifically, when the blockage ratio drops from 0.438 to 0.365, the maximum reductions in pressure amplitude and average longitudinal airflow velocity reach 33.57% and 59.69%, respectively. When the train operates at the maximum speed of 120 km/h in a tunnel with a blockage ratio of 0.438, only the airflow velocity in the head car remains within the acceptable range for passengers. These findings provide essential data to support the design of tunnel parameters for metro express lines.