Prediction of the formation of backdraft in a compartment based on large eddy simulation

Purpose - To investigate the fluid structure of gravity current in backdraft consisted of the hot gas and the ambient air, to predict the ignition time for backdraft and to study the effect of opening geometries on the ignition time. Design/methodology/approach - Numerical models based on large eddy simulation in fire dynamics simulator are adopted to study the ignition time. Findings - The density (temperature) profiles and velocity fields from the numerical simulation show the typical fluid structure of gravity current, i.e. the slightly raised head, the billows formed behind the head and the lobes and clefts at the leading edge. The increased mixing of gravity current by the ceiling opening geometries comparing to the mixing by the end opening geometries is a result of the three-dimensional flow. The non-dimensional velocity presented here is independent of the different normalized density differences, and only depends on the different opening geometries. From this result, it is feasible to predict the ignition time for backdraft in a compartment. Originality/value - This paper provides a method for predicting the ignition time for backdraft, and offers helps for people, especially firefighters, avoid the hazard from backdraft.