Gusts caused by high-speed trains in confined spaces and tunnels

Little is known of the behaviour of transient air velocities and dynamic pressure loads generated by high-speed trains in confined spaces, or whether current methodologies for assessing transient gust loads in open spaces can be used in confined spaces. Experiments have been carried out in which a moving-model high-speed train passed walls, a partially-enclosed tunnel, and single-track tunnels with a variety of cross-sectional areas and lengths. An open air control experiment has also been carried out. The train model was a simplified 1/25 scale four-carriage ICE2 train travelling at 32 m/s. Cobra Probes measured the three-dimensional air velocity components at various positions inside the structures. The results show that the peak gust magnitudes increase in all confined cases compared to the open air. In tunnels, a ‘piston effect’ appears to have been a dominant cause of the increases in the peak gust magnitudes, as well as prolonged winds occurring before and after the train passed the probes. The tunnel length impacted considerably on the flow characteristics, and the partially-enclosed tunnel showed further increases in the gusts due to high lateral and vertical velocities.