Cab top-view variant gene for the aerodynamic shape design of high-speed train heads

Abstract This study examines whether a local top-view variation in the cab region of high-speed train heads can be converted into a measurable design variable that maintains pedigree continuity while supporting aerodynamic decision-making. A cab top-view variant gene, θ, was defined from late-stage Shinkansen models as the angle between the local cab-sidewall trend line and the reference trend line of the main car-body sidewall. Six E2-Series-based models with θ values from 0° to 15° were evaluated using transient numerical simulations at 350 km/h under open-air and tunnel conditions. Increasing θ reduced the three-car drag coefficient from 0.336 to 0.317 and the tail-car lift coefficient from 0.122 to 0.108. Tunnel pressure responses were strongly location dependent: monitoring points near the cab and streamline-transition region were substantially more sensitive to θ than mid-car points. Surface-pressure results further showed weakened positive-pressure and suction regions around the cab transition. θ is not merely a styling descriptor, but a local pedigree-variation parameter with an interpretable aerodynamic effect. It links pedigree recognition, local slenderness control, sectional-area regulation, and aerodynamic assessment, thereby supporting early-stage high-speed train head-shape design.