Shaogang Zhang

Effects of shaft inclination angle on the capacity of smoke exhaust under tunnel fire

Vertical shaft is one of the most important approaches for smoke control under tunnel fires. However, the boundary layer separation is a common phenomenon of hampering the smoke exhaust for vertical shafts. A tilted shaft has been proposed to solve problems and improve the capacity of smoke exhaust. In this study, the effect of shaft inclination angle (θ decreases from 90° to 14°) and shaft height on the capacity of smoke exhaust was addressed numerically. A series of scenarios were simulated in a full-scale road tunnel. Numerical results showed that the tilted shaft could eliminate the boundary layer separation. However, small shaft inclination angle could lead to a relatively higher resistance to the smoke and a smaller cross-section area of shaft, which could have an adverse effect on the capacity. Under these two factors, an optimal inclination angle exists in the shaft of around 76° in this study. Based on the smoke flow characteristics and exhaust effect, the inclination angle was roughly divided into three regions. The main influence factor of the inclination angle on the mass flow rate of smoke in each region was examined. For a comprehensive consideration, the low and slightly tilted shaft was applied to tunnel fires, which can improve the capacity of smoke exhaust obviously.

The Influence of Train on the Smoke Movement in Subway Tunnel with Longitudinal Ventilations

The smoke movement in the subway tunnel with train under different longitudinal ventilations was simulated using Fire Dynamics Simulator (FDS) program in this paper. The influence of subway train on the characteristics of smoke flow, including the smoke temperature underneath the tunnel ceiling and back-layering length, were investigated. The results showed that the upstream smoke gas temperature was much lower with train than without when the ventilation velocity was lower than the critical value and the downstream dimensionless smoke gas excess temperature decayed exponentially. The subway train could contribute to reduce the back-layering length at low ventilation velocities. Meanwhile, the FDS simulated smoke back-layering length agreed well with the calculated values of the proposed model. However, the difference between train lengths of 20 m and 40 m was insignificant. The mechanism of the train influence was discussed in depth using hydrodynamics.