The impact of rails on high-speed train slipstream and wake.

Slipstream is the induced movement of air as a high-speed train (HST) passes. Previous studies have shown that the development of slipstream is highly geometry dependent, including both the geometries of the trains and nearby objects. Much effort has been channelled into reducing slipstream through optimisation of the train geometry; however, the impact of the rails on train aerodynamics remains largely unexplored. This study analyses the effect of rails on HST slipstream characteristics by systematically comparing the wakes for two geometric configurations incorporating: No Rails (NR) and With Rails (WR). The train model remains identical in both configurations, with the only difference being whether rails are included. This study highlights the potential effects of rails on HST slipstream characteristics, and reveals the underlying mechanism of how the rails shape the wake flow structures. By examining both mean and time-dependent flow features, the simulations show that the rails can significantly alter slipstream characteristics, especially the downstream evolution of the wake, effectively by reducing the lateral movement of the mean streamwise vortex structures, despite the relatively small length scale of the rail cross-section. Perhaps surprisingly, the slipstream measured at the standard distance from the train centerplane, is found be significantly reduced. • The study examines the differences between two models, with and without rails, as both models were adopted in the literature. • This study highlights the potential effects of rails on high-speed train slipstream. • This study further reveals the underlying mechanism of how the rails shape the wake structures. • This study provides insight in formulating the best practice for numerically predicting high-speed train slipstream. [ABSTRACT FROM AUTHOR]