Experimental evaluation and real-time forecast of smoke propagation in tunnels under intervention of sub-critical longitudinal ventilation

Abstract

Sub-critical longitudinal ventilation can restrict the back-layering length in the upstream region and maintain suitable smoke stratification in the downstream region of a tunnel fire. In this study, experiments using a 1/15 scale, 80-m long, 1.2-m wide, and 0.5-m high model tunnel were conducted to investigate the effects of sub-critical longitudinal ventilation velocity and heat release rate (HRR) on the key parameters describing smoke propagation. The smoke front temperature near the fire source decreased significantly as the longitudinal ventilation velocity increased. The longitudinal ventilation velocity and HRR were incorporated into a regression model describing the smoke front velocity, which was applied to the evaluated fire scenarios using an ensemble Kalman filter to account for intervention of sub-critical longitudinal ventilation. The smoke front temperatures at discrete locations were assimilated to estimate the heat exchange correction coefficient and air entrainment ratio of smoke front in real-time and dynamically correct the forecasted smoke front temperature and velocity accordingly. When sub-critical longitudinal ventilation intervened, the smoke front parameters could be forecasted with a maximum lead time of 60 s and an average error within 5%. Therefore, the proposed forecasting method can inform the selection of disposal measures in early tunnel fire emergencies.