Aerodynamic anti-overturning optimization of high-speed trains with airbag structures under crosswind

Under crosswind conditions, multiple flow separations occur in the leeward side (LWS) region of the trains, leading to the formation of large-scale vortical structures that reduce surface pressure and generate significant lateral aerodynamic loads. Disrupting these large-scale vortices and increasing the LWS pressure therefore represents a promising approach to improving the anti-overturning performance of high-speed trains. In this study, numerical simulations were performed to investigate the flow-field characteristics around the train equipped with airbag structures (ASs) installed on the LWS. The improved delayed detached eddy simulation turbulence model was employed to evaluate the flow-control effectiveness of the ASs and its influence on aerodynamic performance under crosswind conditions. The results show that the ASs effectively reduce both the lateral force and overturning moment by modifying the dominant leeward vortices, shifting them away from the train body, and splitting the near-body vortex into two smaller vortices. These flow-field alterations improve the pressure distribution on the LWS, thereby mitigating adverse aerodynamic loads. Compared with the baseline configuration, the lateral force and overturning moment coefficients decrease by 3.84% and 6.49%, respectively, with the AS configuration. In addition, the installation of the ASs influences lift characteristics, increasing the lift coefficient of the middle car by 41.58% and that of the entire train by 10.94%. The present study proposes a novel passive flow-control strategy for enhancing the operational safety of high-speed trains subjected to crosswinds.