Influence of platoon configuration on train aerodynamic performance under crosswind conditions

Virtually coupled train formations have gained increasing attention due to their potential to enhance transportation efficiency. This paper investigates the aerodynamic behaviors of virtually coupled trains with various platoon spacings under crosswind conditions. As the platoon spacing approaches D/H = 2.5, the mean aerodynamic coefficients Cd, Cs, and Cl(where Cd, Cs, and Cl denote the drag, side-force and lift coefficients, respectively.) for the tail of the leading train approach 1. However, the ratios of forces for the head of the trailing train remain below 1 due to the extended wake of the leading train. The sums of Cd and Cs for the tail car (T3) of the preceding train and the head car (T4) of the following train consistently decrease as the platoon spacing decreases within the considered range, while the sums of time-averaged Clfor T3 and T4 exhibit the opposite trend. Instantaneous slipstream on the leeward side displays significant run-to-run variation, in contrast to the windward side. The double-unit region contributes to a nearly constant mean value and standard deviation of the streamwise slipstream velocity component when the platoon spacing exceeds 0.625H. Flow field structures are visualized, revealing a strong shielding effect introduced by the double-unit region. As the platoon spacing increases, T4 remains within the wake of T3, but the velocity deficiency in this region recovers. The findings from this research provide fundamental insights for supporting control strategies aimed at reducing energy consumption and ensuring operational safety for virtually coupled trains operating under crosswind conditions.