Field study on the interior pressure variations in high-speed trains passing through tunnels of different lengths

As a high-speed train passes through a tunnel, the intense aerodynamic pressure wave outside the train penetrates into the passenger compartments, changing the pressure environment inside the train and causing discomfort to passengers. This phenomenon varies enormously among tunnels of different lengths. To evaluate the real influence of tunnel length on the interior pressure environment of the carriages and ensure passenger comfort, field measurements were conducted on a CRH2A train operating on the Hefei-Wuhan rail line in China; twelve tunnels with lengths ranging from 72 to 10766 m were investigated. Pressure sensors were deployed along the outside and inside train surfaces to investigate the variations in interior pressure with the exterior pressure environment. The results show that the interior pressure curve over time in a short tunnel has a single-trough form, very different from that in a long tunnel. The total variation of interior pressure increases monotonically with tunnel length from 72 to 10766 m, whereas the maximum pressure variation within a 3 s period occurs in the 1080 m tunnel; the variation within a 1 s period is not significantly affected by the tunnel length for tunnel lengths greater than 556 m. There is a delay in the 1 s interior pressure variation in response to an exterior pressure change; this delay is independent of the tunnel length and is approximately 1.2 s in this test. It is found that the reason for passengers' ear discomfort in very long tunnels, which is mainly an effect of excessive changes in pressure over a long period of time, could be different from that in long or short tunnels.