The Influence of Oblique Tunnel Portals and Blockage Ratio on the Aerodynamic Performance of Urban Rapid Rail Tunnels

The study aims to understand the differences in aerodynamic pressure between urban rapid rail (URR) transit and high-speed railway tunnels caused by different tunnel portal structures. In this paper, a three-dimensional compressible turbulent flow model is used to simulate trains entering tunnels with three portal forms. The effects of tunnel portal forms and blockage ratio on the aerodynamic interaction between trains and tunnels are analyzed. Using full-scale test data, the reliability of simulating train entry into the tunnel is verified. Based on validated simulations, peak values and maximum pressure gradients are investigated for the three scenarios mentioned above. As a result, the transient pressure caused by the three types of inclined portals does not differ significantly, but it affects a train's surface pressure varies over time. The ring oblique and reversed ring oblique portals both reduce primary compression wave's maximum pressure gradient, while reversed ring oblique portals exhibit better performance. In addition, the study also identifies a critical blockage ratio $β*$⁠, which determines the opposing effects of the two portal types in mitigating the aerodynamic interaction.