Description
Smoke control in the case of a tunnel fire is vital to ensure an atmosphere allowing tunnel users to evacuate. Depending on the type of ventilation, namely the longitudinal or the transverse ventilation system, the aim is respectively either to push the smoke longitudinally towards a tunnel exit or to evacuate the smoke transversally by the tunnel ceiling. In both cases, a sufficient mechanical airflow is required to prevent any smoke back-layer and ensure an efficient smoke exhaust.
Previous experimental investigations in small-scale tunnels have shown the potential of geometrical optimizations in order to increase the robustness of smoke exhaust ventilation systems. The shape of dampers of the transverse ventilation strategy was questioned. Wide rectangular dampers appeared to be significantly more efficient than narrower or square dampers, which are commonly installed. Reducing the required airflow goes along with reducing the power requirements of the ventilation system. It tackles the issues of energy consumption and the improvement of the robustness of existing ventilation systems. It also eases the dimensioning and cost of ventilation systems installed in new tunnels. Further experimental investigations questioned the alteration of the transverse system performance due to a longitudinal natural airflow. The smoke behavior as well as the confinement velocity were assessed for several speeds of the longitudinal natural airflow and for different shapes of damper. The benefit brought by rectangular dampers was verified for several intensities of the natural airflow.
The present work aims at reproducing these experiments numerically thanks to a Computational Fluid Dynamics model. It intends to verify the potential of wide rectangular dampers under the influence of a natural airflow. In the case with no natural airflow (i.e. in the optimal configuration), the benefit of rectangular dampers is about 80% compared to reference sided square dampers. However, under strong natural airflows, the benefit of rectangular dampers became negligible.
