An adaptive drag reduction method for high-speed trains across variable Reynolds numbers

This paper investigates a passive flow control method for high-speed trains using strategically positioned vortex generators (VGs) to simultaneously address drag reduction and slipstream suppression across varying Reynolds numbers. Through validated improved delayed detached eddy simulations, the aerodynamic forces, flow structures, and wake dynamics are analyzed. The results show that the drag of the tail car is reduced by ∼3% with varying Reynolds numbers, while the lift of the tail car is reduced by ∼60%. The mechanism for the drag reduction is the increased pressure on the upper surface of the tail car, which achieves the drag reduction by ∼30% due to the installation of the VGs. The installation of VGs introduces the opposite-sign counter-rotating vortices, which decelerate the downwash flow and prevent the interaction between the trailing vortices of the train and the ground, contributing to the drag reduction and slipstream suppression. Furthermore, the mean slipstream velocity is found to be reduced by ∼20% with VGs, and the standard deviations are suppressed more significantly as the Reynolds number increases. These findings support the application of VGs on the train aimed at improving aerodynamic performance for high-speed operation.