A Study on the Effect of Auxiliary Measures on the Suppression of Smoke Backflow Behavior in Multi-shaft Natural Exhaust Tunnels

During a fire in a naturally ventilated tunnel with multiple vertical shafts, some shafts may induce supplementary airflow, leading to destabilization the smoke layer and potentially causing smoke to ingress back into the tunnel interior, thereby compromising the safety of trapped occupants. This study investigates the dynamics of smoke propagation in tunnel fires under natural ventilation conditions in multiple shafts using numerical simulations. Various auxiliary measures to mitigate the destabilization of the smoke layer in the tunnel as well as to suppress the smoke propagation are proposed and evaluated. The research findings indicate that installing auxiliary fans inside the shafts or incorporating coupling plates beneath them can effectively attenuate the extent of smoke ingress to varying degrees. While these measures have a small effect on smoke removal efficiency, the auxiliary fans mitigate the collision between smoke flow and supplementary air by regulating the flow field at the bottom of the shaft, maintaining a stable smoke layer flow state and suppressing smoke backflow. Coupling plates increase resistance to horizontal smoke spread. This constrains smoke spread and prevents smoke flow from colliding head-on with supplementary air, which could cause backflow. In summary, this research enhances understanding of the intricate dynamics of smoke propagation in tunnels with multiple shafts during fires and offers insights to refine the design of natural ventilation systems in tunnels.