Mechanism of spillage plumes from multiple openings on ceiling temperature distribution in metro tunnel fires based on superposition principle

This study revisits the coupling effects of tunnel ceiling temperature distribution caused by plume escapes from metro carriage doors during a fire. The impact of fire heat release rates on the ceiling temperature distribution under various door-opening scenarios was analysed by utilising the superposition principle. The concept of virtual fire sources was proposed to model the ceiling temperature distribution associated with plume outflows from carriage doors. The results indicate that the ceiling temperature distribution in a metro tunnel fire is primarily influenced by virtual fire sources generated by plumes escaping through multiple doors. The maximum ceiling temperature from a single virtual fire source was significantly lower than that of a real fire, and the temperature decay followed a double exponential function. The heat flow ratio for each door remained nearly constant for different fire heat release rates, and variations in heat flow with door positions were analysed. The incorporation of heat loss terms into the theoretical model improved the accuracy and quantification of heat loss coefficients. A predictive model for the ceiling temperature distribution caused by metro carriage fires was developed based on the superposition principle, with the predictions well aligning with the experimental results. This study enhances our understanding of the ceiling temperature distribution in multi-opening structures and guides scenarios involving multiple fire sources within tunnels.