Numerical study on the flow characteristics and smoke temperature evolution under double fires condition with a metro train in tunnel

Metro system as the most effective transportation method in urban area, greatly relieve the traffic pressure. The fire safety problem of metro system cannot be ignored as it is easy to develop into a large-area fire due to the relatively closed condition of the metro system. Double fire source is an important process in the development to large-area fire, however, there is still no relevant researches studying the flow characteristics and smoke movement under double fire sources with a metro train in the tunnel. This paper conducted a series of the full-scale numerical simulation to investigate the evolution of longitudinal temperature profile and maximum temperature rise under condition of double fire source with metro train in the tunnel. The velocity and temperature profile along the tunnel ceiling was measured and analyzed. It is found that (1) the longitudinal temperature distribution of tunnel fire smoke is still exponentially attenuated under different fire source separation distance with a metro train in the tunnel, and the decay coefficient decreases with the increase of fire source separation distance; (2) the maximum temperature rise of fire smoke under the tunnel ceiling decreases with the increase of the distance between the fire sources. Correlations were developed to describe the longitudinal temperature profile and maximum temperature rise under condition of double fire sources with a metro train in the tunnel through the analysis of the effect of additional air entrainment area, smoke interaction as well as the blockage effect of the metro train. The new findings in this paper can provide basic understanding of smoke movement under condition of double fire sources with a metro train in the tunnel, the proposed correlations can provide support for the safety operation of the metro system.