Study on control of upstream smoke propagation in road tunnels by using a side-wall sprinkler system

Abstract

Side-wall sprinkler systems used for fire suppression in road tunnels have been found to redistribute the longitudinal air flow within the tunnel, with the most notable feature being an acceleration of the airflow near the ceiling. The present work is driven by the motivation of utilizing the acceleration effect to block the upstream smoke propagation in cases when the ventilation rate is sub-critical. A nozzle prototype that has practical applications in road tunnels was selected for a side-wall water spray system in a 300 m road tunnel, and a total of 60 cases were modelled using the CFD code FDS (version of 6.7.3) to investigate its smoke blocking effect. Experiments and correlations in the literature have validated the accuracy of the FDS method. The confinement velocity reduction rate, which is determined as the reduction of the ventilation rate required to stop the smoke front point at a given position, was found to be positively affected by both the water spray rate and the ventilation rate and was successfully correlated using dimensionless momentums of these two factors. By comparing the confinement velocity reduction rates with the increases in the ceiling velocity in the absence of tunnel fire, utilization efficiencies of the spray-induced accelerations were further obtained.