Abstract: Multiple-car trains stably run at 160 km/h on open tracks, but the tail car periodically shakes in the lateral direction when traversing through single-track tunnels. In this study, a coupled solution method for the flow field and vehicle dynamics during train operation is proposed by integrating overset grid technology and fluent user-defined functions. The validity of this calculation method is verified through on-site vehicle tests. Subsequently, the effects of the tunnel blockage ratio on the trailing vortex structure, aerodynamic forces, and lateral shaking of the tail car are systematically analyzed. The results reveal the following: (1) When the blockage ratio exceeds 0.350, the trailing vortex structure of the train is confined to a narrow horizontal space, weakening alternating vortex shedding. At the same time, the flow field on both sides of the nose section of the tail car is approximately symmetrical, resulting in a small lateral force acting on the carriage. For tunnels with cross-sectional areas of 35.20 m² (blockage ratio is 0.309) and 42.06 m² (blockage ratio is 0.259), the lateral force amplitudes of the tail car are 2 332 N (－2 483 N) and 2 430 N (－2 499 N), respectively. (2) A decrease in the blockage ratio exacerbates the lateral shaking of the tail car. However, the growth rate of shaking intensity decreases once the tunnel cross-section is expanded to a certain extent. When the train passes through the 35.20 and 42.06 m² tunnels, the dominant frequencies of the alternating lateral force on the tail train are 2.05 and 2.20 Hz, respectively. As the blockage ratio decreases, the dominant frequencies of both the lateral force and lateral acceleration increase.

Key words: single-track tunnel, blockage ratio, aerodynamic force, lateral shaking of tail car, coupling solution, trailing vortex structure