Bio-inspired shark fin installed beneath the tail car for multi-parameter drag reduction optimization of 400 km/h high-speed trains

As the speed of high-speed trains surpasses 400 km/h, aerodynamic drag becomes the dominant component of total resistance. To address the limitations of passive devices and the complexity of active control systems, this study proposes a triangular biomimetic shark fin structure (BSFS) installed beneath the tail car fairing. Computational fluid dynamics and the response surface method are employed to optimize seven key parameters: length (l), height (h), leading-edge angle ( θ ), rotation angle (r), spacing (S), and installation positions (d, α ), establish a second-order response surface model with drag reduction rate as the objective and analyze the interaction effects of multiple parameters. The results indicate that the optimal parameter combination (l = 0.78 m, h = 0.33 m, θ = 130°, r = 7.4°, S = 0.75 m, d = 0.28 m, α = 24.4°) reduces the tail car drag by 4.50%, and the whole train drag by 2.03%. This configuration significantly improves the tail flow field characteristics, reducing the vortex volume by 25% and achieving an energy dissipation suppression rate of 18%. Additionally, it reshapes the pressure field by enlarging the positive pressure zone at the tail car nose tip by 32% and reducing the leading-edge negative pressure zone. This research pioneers the multi-parameter optimization of BSFS for wheel-rail trains, offering a novel aerodynamic solution with strong engineering potential.