Aerodynamic shape effects on fluid–structure coupling vibration of train tail inside a small cross section tunnel

Inside small cross section single-track tunnels, the ride comfort for drivers and passengers has been considerably impacted by the sustained lateral swaying in the tail car of the 160 km/h power-concentrated electric multiple unit (EMU). Nevertheless, previous studies have mostly focused on unilateral train aerodynamics or vehicle dynamics. Systematic investigations into the mechanisms governing fluid–structure coupling vibrations in trains inside tunnels remain insufficiently explored. Therefore, a fluid-structure coupling simulation platform for 9-car marshaling train aerodynamics and vehicle dynamics is constructed, and the accuracy and efficacy of the coupling method are validated through on-track tests. On this basis, aerodynamic loads and dynamic responses of the carbody while EMUs traverse tunnels are investigated. Furthermore, the effects of differing carbody lengths and head shapes on coupling characteristics are examined. The results indicate that the front and rear ends of the carbody are subjected to aerodynamic loads, which induce carbody lateral displacement and rotational motion. The coupling effect alters the amplitude and frequency of aerodynamic loads with aerodynamic load frequencies synchronized to carbody vibration frequencies. Harmonic vibration is obviously detected at both the front and rear ends of the carbody with the rear end exhibiting greater intensity. The aerodynamic shape of the tail car predominantly affects the intensity of aerodynamic loads. The vibration frequency of the carbody is primarily influenced by two factors: the train's running velocity and the interplay between the carbody's dynamic response and the surrounding flow field. This work can provide a reference for the aerodynamic shape optimization of trains traversing tunnels.