Effects of vortex generators on the aerodynamic performance of high-speed tail cars with various streamlined head lengths

When the air flows over a high-speed train rear, flow separation occurs, generating a pair of counter-rotating wake vortices. These vortices not only significantly affect operational stability, but also constitute a major source of aerodynamic drag. This study aims to explore a passive flow control approach by installing vortex generators (VGs) with identical parameters on high-speed tail cars featuring different streamline lengths, and investigate its influence on the aerodynamic performance of tail cars, at a Reynolds number of 3.0 × 106. The accuracy of the numerical method has been validated by wind tunnel experiment. The tail car with a 7.89 m streamline length achieves a 5.3% drag reduction and a 19.3% lift reduction after VG installation; the tail cars with 9.9 and 12.5 m streamline lengths exhibit no significant drag change, but with lift reductions of 20.7% and 35.1%, respectively; the tail car with a 5.5 m streamline length shows negligible drag change and a limited lift reduction of only 9.5%, which is far less effective than that of other streamlined configurations. Flow field analysis reveals that the 5.5 m streamline tail car fails to effectively suppress flow separation and vortex development near the tail after installing VGs, whereas those are well controlled in other cases. Further analysis demonstrates that only when the VG match the local geometry of the tail car can achieve improvement in train aerodynamic performance. This paper contributes to better understanding the controlled wake flow of high-speed trains with VGs, which provides support for the potential application of VGs on the high-speed train.