Research on the aerodynamic comfort and safety of high-speed trains when extracting air from inclined shafts in tunnels

• Three-dimensional numerical simulations were conducted to investigate the aerodynamic effects of air extraction through inclined shafts in tunnels. • The influence of key factors, including train speed, air extraction velocity, and lateral train-to-shaft distance, was systematically analyzed. • The operational safety and passenger comfort of high-speed trains in existing tunnels under inclined shaft air extraction were evaluated. This study investigates the aerodynamic comfort and safety of high-speed trains (HST) running within existing tunnels when the air is extracted through inclined ventilation shafts. Three-dimensional numerical simulations were performed to assess the transient pressure variation at the train body and the wind pressure load surrounding the slant shaft under three typical scenarios, i.e., the inclined shaft is closed, the shaft is opened without air extraction, and the air extraction is activated. Influencing factors were successively revealed, e.g., train speed, air extraction velocity, the lateral distance between HST and shaft, and the position of HSTs’ intersection. The major findings are listed as: 1) Shaft is useful in decreasing the transient pressure amplitude at the train body while air extraction through the shaft has limited impact. 2) As the shaft is opened, the wind pressure load at the side of the train closer to the shaft is diminished, whereas the pressure load at the opposite side increases. Pressure decrease in the condition of air extraction case is not significant compared to those measured in the non-air extraction case, yet the increase in lateral wind pressure load is more significant; 3) In the air extraction case, overturning coefficient of HST is inversely related to both the train speed and the lateral distance to the shaft and is positively correlated with the air extraction speed; 4) During train crossing events within the tunnel, the farther the crossing location is from the ventilation shaft, the smaller the lateral forces and overturning moments experienced by the train; 5) When the train speed is 350 km/h, the air extraction velocity is below 10 m/s, and the tunnel cross-sectional area is 70 m² during air extraction from the inclined shaft, the 3-second transient pressure peak inside operational trains within existing tunnels is <800 Pa, and the overturning coefficient is below 0.8, the operational comfort and safety conform to established standards.