Evolution of flow field around high-speed trains meeting at the tunnel entrance under strong wind-rain environments

Tropical storms pose a great threat to the traffic safety of tunnel-embankment transition sections in coastal areas, especially when two trains are meeting. A series of 3D computational fluid dynamics numerical simulations of wind-rain-tunnel-embankment-train are established using the Eulerian multiphase and the Shear-Stress Transport k-ω models. The numerical model's reliability is verified by wind tunnel tests using rainfall simulation technology. The differences in the train's aerodynamic performance before and during the meeting under different wind-rain conditions are analyzed. The rain phase's impact mechanism on the flow field is revealed. Results show that: Before the meeting, the rain phase will worsen the train's aerodynamic performance. When the wind speed and rainfall intensity is 20 m/s and 400 mm/h, the head train's average lift force (C‾_y), yawing and pitching moments (C‾_mz) increase by 6.25%, 9.68% and 10.31%, respectively. The rain phase increases the wind-rain load amplitude during the meeting, and the head train's pitching moment increases by 10.7%. The moment is more worthy of attention than that of force under a rainy day, and the change rate of C‾_mz is 4.9 times of that of C‾_y. The amplification effect of rain on wind-rain loads may endanger the driving safety of trains at the tunnel entrance.