Flow simulations of a high-speed train to investigate the ballast flight

Related to the train underfloor carbody aerodynamics, a phenomenon of ballast flight occurs frequently associated with the operation of high-speed railways. The flow developed beneath a high-speed train running on a ballasted track and around the ballast particles is turbulent and has strong influence on the ballast flight. This paper investigates the aerodynamic behaviour of the flow passing by a scaled high-speed train with ground underneath using computational fluid dynamics based on the delayed detached-eddy simulation. It is found that the flow field is highly unsteady due to strong flow separations and interactions developed around the train various areas, such as the nose car, leading bogie, articulated bogie and tail car, etc. It is found that compared to the region below the top of the rail, the flow fluctuations are higher above the rail owing to a highly unsteady flow generated there. Moreover, the strong flow interaction is produced around the articulated bogie due to its special location between the inter-car gaps. The significant pressure pulse produced around the nose, tail and train inter-car gaps will make the ballast flight occur easily. Therefore, reducing the flow interactions around the nose car, tail car, inter-car gaps and other areas with the surface shape discontinuities will lead to less fluctuating forces on the ballast particles, which will reduce the occurring of the ballast flight for high-speed railways.