Investigation of dynamic airtightness thresholds for high-speed maglev trains under different tunnel lengths

Abstract

High-speed maglev trains (HSMTs) operating at 600 km/h encounter pronounced tunnel aerodynamics, which induce internal pressure fluctuations that may impair aural comfort. This study investigates the dynamic airtightness thresholds (τ_thr) of a four-car maglev train under varying tunnel lengths. A one-dimensional compressible unsteady flow model based on the method of characteristics is employed to predict external pressure variations. These results are then used to compute internal pressure and pressure change rates. The corresponding τ_thr required to satisfy comfort criteria (500 Pa/s, 800 Pa/3s, 1000 Pa/10s) for each carriage is determined using a binary search algorithm. For tunnel lengths exceeding 300 m, the pressure waveform remains stable. Externally, positive pressure peaks attenuate along the train, while internally, negative pressure accumulates toward Carriage 4, imposing the most stringent airtightness requirements. With increasing dynamic airtightness coefficient, the internal pressure response to external aerodynamic loads is mitigated, leading to a reduction in the maximum pressure change rate. For Carriage 4, the most unfavorable tunnel lengths are 500 m, 600 m, and 2000 m under the 500 Pa/s, 800 Pa/3 s, and 1000 Pa/10 s criteria, respectively. When the tunnel length is below 10000 m, the corresponding τ_thr values are 10.11 s, 15.97 s, and 39.26 s. For tunnels exceeding 10000 m, τ_thr exhibits a power-law dependence on tunnel length. This study provides quantitative guidance for the airtightness design of HSMTs.

Keywords

high-speed maglev trains / railway tunnel / pressure waves / internal pressure / dynamic airtightness threshold

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