Numerical Simulation And Mechanism Research Of Backdraft Phenomenon In Building Fire

When the fire happen in the enclosed space, gas exchange cannot be performed between indoor and outside. Then the burning will be extinguished as the oxygen concentration indoor falls below some certain level. But still fuel gas is being decomposed from the combustible material in high-temperature circumstance. For some reason, such as windows burst or door break up, if the confined space vents, a gravity current is forming by the fresh air flowing into the space from below of the vent and the hot smoke flowing out from the top of the vent. If the explosible mixture is ignited or the mixture temperature high enough to self-ignite, violent combustion even explosion will occur. In the secondary fire caused by the mixture gas, the flame will spray out of the enclosed space like fireball which is so high in temperature and gas pressure that the building construction can be damaged fatally. All of this are the backdraft phenomenon in building fires. This article will explain the backdraft phenomenon in the way of computer numerical simulation and theoretical analysis.1) Citing most types of mathematical models of numerical simulation and analyze the specialty of each one. Different mathematical models correspond to different initial conditions, therefore which combustion model satisfy the need to analyze backdraft phenomenon should be discussed. By comparing the major five types of mathematical models for fire research, the field simulation which is based on turbulence mechanical model needs the least initial assumptions howerver its data the model run out is more accurate than anyone. One kind of field simulation, large-eddy simulation, has good application prospect for its tolerance to computer hardware. The mixture fraction combustion model is set up to perform the combustion reaction in large-eddy simulation, which meet the research needs by analyzing in detail.2) The fire model of a real fire case including backdraft phenomenon,"62WATTS ST.(NY) FIRE", using FDS software should be set up and analyzing the data curve containing the heat release rate, temperature and the carbon monoxide concentration. By compared with previous research findings, it is proved that the FDS software based on field simulation is more viable to exhibit the course of backdraft phenomenon.3) Referenced to previous small-scale experimental data, the types and critical condition of backdraft are concluded based on the theory of thermal equilibrium.