Efficiency of a smoke curtain in a ventilated tunnel

TL;DR

This study uses numerical simulations to analyze how smoke curtains interact with ventilation in tunnels, showing that properly sized curtains can reduce required ventilation velocities and improve smoke containment.

Contribution

It provides new insights into the combined effects of smoke curtains and ventilation on smoke behavior in tunnels through detailed numerical analysis.

Findings

Vortex size downstream of curtain depends on velocity and curtain height.

Properly sized curtains can reduce the ventilation velocity needed for smoke containment.

Curtains interact with smoke, increasing local smoke layer thickness.

Abstract

Smoke curtains are typically used in public-access buildings in connexion with ventilation effects without considering a crossed design. This paper aims to understand the fire smoke behaviour in the context of the interaction between mechanical ventilation and smoke curtains. This interaction is analysed here in the configuration of a tunnel with using numerical simulations. Initially, without the presence of fire smoke, the length of the vortex induced downstream of the curtain is determined as a function of the longitudinal velocity and the size of the curtain. It can be observed that for a sufficiently high velocity (i.e. a sufficiently high Reynolds number), the size of this vortex depends only on the height of the smoke curtain. Then, in the presence of a moderate fire heat release rate, we determined the air velocity required to prevent smoke from rising beyond a curtain measuring 1/5 the height of the tunnel. A significant reduction in this longitudinal velocity was observed in comparison to the velocity required to achieve the same level of containment without the presence of a curtain. The vortex generated by the curtain nevertheless interacts with the smoke layer, locally increasing its thickness. Lastly, this configuration is tested in the case of a medium and high fire heat release rate in a road tunnel with transverse ventilation. The work carried out suggests that the installation of smoke curtains of an appropriate size, combined with control of ventilation effects, is likely to reduce the need for them.