Effect of Expansion Wave Generated by Train Tail Entering into Tunnel on Lateral Vibration of High-Speed Train (original) (raw)

Abstract

It is well known that the lateral vibration of the trains running in tunnel becomes larger than that at open section, where we cannot find strong relevance to track irregularity in contrast to the vibration at open section. This vibration has been explained mainly by the aerodynamic flow separation and vortex shedding from the surface of trains. In this paper we focus on lateral vibration of the high-speed train (Shinkansen), and try to investigate not only flow separation but also expansion wave effect from the tail part of the trains on the vibration when they enter the tunnel. We have started to investigate with compressible and two-dimensional numerical analysis of aerodynamic flows around the trains. For the trains entering the tunnel, we performed the CFD with ghost cells and level set functions. As a result of interference of expansion waves and aerodynamic flow separation and alternating periodical expansion waves passing the train sides, large pressure difference on both sides of the trains moving forwards from the tail to the top is raised, which causes the lateral vibration.

Key takeaways

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1. Expansion waves significantly impact lateral vibration of high-speed trains entering tunnels.
2. Aerodynamic flow separation and vortex shedding contribute to increased lateral vibration, especially at speeds over 250 km/h.
3. Pressure differences caused by interaction of expansion waves and vortices lead to complex lateral vibrations.
4. Field measurements recorded strong acceleration onset when trains enter tunnels, with a peak PSD shift from 1.2 Hz to 2.2 Hz.
5. Future research will utilize three-dimensional simulations to further analyze aerodynamic effects on train dynamics.

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References (10)

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FAQs

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What role do expansion waves play in lateral train vibrations during tunnel entry?add

The study reveals that expansion waves significantly increase lateral vibrations by creating pressure differences, with strong interference observed at speeds over 250 km/h. This effect is attributed to alternating wave interactions that enhance vibration magnitudes compared to open sections.

How did numerical simulations contribute to understanding train vibrations in tunnels?add

The research employed two-dimensional numerical simulations of compressible Navier-Stokes equations to visualize pressure distributions and vortex formations. Results showed that these simulations correlated with field measurements, indicating robust interactions between expansion waves and trailing vortices.

What experimental methods were used to measure acceleration of trains in tunnels?add

Field measurements utilized a G-MEN DR01 accelerometer positioned on the 9th car of a Shinkansen. The measurements captured notable increases in vibration during tunnel entries, revealing a peak PSD shift from 1.2 Hz to 2.2 Hz.

Why are pressure differences significant in understanding train vibrations in tunnels?add

Pressure differences between tunnel wall and train surfaces, resulting from expansion waves and airflow interactions, create varying aerodynamic forces. This mechanism is identified as a crucial contributor to the lateral vibrations experienced by trains entering tunnels.

When did the study identify significant lateral vibrations compared to open sections?add

Significant vibrations were detected approximately 5 seconds after the train tail entered the tunnel, showing a peak acceleration response that persisted for 15-20 seconds. This indicates a pronounced effect of tunnel dynamics on train stability during high-speed operations.