Numerical simulation of a subway car fire

Abstract

This research thesis presents the simulation of fire growth and flame spread within a car in an underground trainway using Fire Dynamics Simulator (FDS) realizing Computational Fluid Dynamics (CFD) model. The motivation of the study is to predict the heat release rate (HRR) and specifically the peak value for emergency situations. The existing documents don’t contain recommendations for defining these important parameters. Using of several methods of estimating the HRR for a metro train, it appears that the current methods cannot realistically predict the HRR because factors such as the burning behavior of materials; and the train and tunnel geometries that affect the HRR are not considered. This project attempts to incorporate these factors in the FDS model. Modeling was realized on the base of such main research results as: § fire load of subway car series 81-557 and 81-558 (wood equivalent); § burning rate (full scale experiments). A number of assumptions have been made so that to simplify the model. They were: § passenger doors were opened from one side of car; § fire load was spread on car area; § window failure was simulated, at temperature 300 °C window began to fracture and fall off (temperature was controlled by detectors at center of windows); § ignition of material was initiated by point source; § upper plane of the computational domain is defined as “Open”; § calculation was carried out until the fire load was completely burned out. The size of the computational domain was 40 m long by 12 m wide by 6 m high. Two grid sizes, 0.025´0.025´0.025 m (zone of fire load) and 0.25´0.25´0.25 m (zone above fire load) were used. The simulation time specified for simulation was 2500 s. Results of modeling: § HRR-curve: approximation of HRR-curve for engineering calculations (“design fire”); § value of peak HRR - 12.3 MW; § combustion reaction parameters. The results of the study and the obtained dependence of the heat release rate can be applied in the development, justification of parameters, evaluation of the smoke protection systems efficiency and analysis of people safe evacuation conditions in case of fire.