Bay winds and train aerodynamic effects of high-speed railways at tunnel portals

Frequent extreme wind events in China's coastal regions pose severe challenges to the aerodynamic performance of high-speed trains passing through tunnel portals under strong winds. To reveal the distribution patterns of bay winds at coastal high-speed railway tunnel portals and enhance the operational safety of high-speed trains, this study systematically investigates the bay wind effects and train aerodynamic responses by combining the RNG k-ε turbulence model with the sliding mesh technique. A computational fluid dynamics (CFD) prediction model, based on actual terrain and a high-speed railway tunnel section, is established to dynamically simulate the entire process of a high-speed train passing through the tunnel portal under a crosswind of 20 m/s at a train speed of 350 km/h. The model incorporates the influences of both the oblique-cut tunnel portal and the embankment topography on train aerodynamic performance, and covers twelve incoming wind direction angles (ranging from 0° to 330° at 30° intervals). Based on the research findings regarding the mountainous flow field and train aerodynamic loads, it is found that under incoming flow with wind direction angles of 90° (due west) and 270° (due east), the flow acceleration induced by the mountain slope results in the maximum average wind speed at the tunnel portal, which increases by 26.5% and 29.0% compared to the incoming wind speed, reaching 25.3 m/s and 25.8 m/s, respectively. Conversely, at wind direction angles of 120° and 150°, the terrain blocking effect is most pronounced, reducing the portal average wind speed by 56.5% and 51.5%, corresponding to values of 11.3 m/s and 10.3 m/s. When the train passes through the tunnel portal section, the aerodynamic loads fluctuate drastically, and the fluctuation amplitude of the head car is significantly higher than those of the middle and tail cars, being 1.34–4.34 times that of the middle car and 2.27–5.66 times that of the tail car. Further analysis reveals a significant positive correlation between embankment height and the fluctuation amplitude of train aerodynamic loads, which can be well described by a linear function with a coefficient of determination (R²) above 0.89. This research can provide a solid theoretical basis and engineering guidance for the route selection and wind-resistant design of high-speed railways in coastal areas.