Numerical Investigation on the Asymmetric Flow Characteristics of Two Propane Fires of Unequal Heat Release Rate in Open Space

Multiple fires of unequal heat release rate (HRR) is a common fire scenario in real fire accidents. Differing from most previous research assumption of identical fire sources, the unequal HRR for those fire sources is regarded as more reasonable in reality. To explore the asymmetric flow characteristics surrounding multiple fires under such circumstances, simulations of two square propane burners with the same side length but different HRRs were carried out. The HRR combination and burner separation distance were varied. The results showed that the asymmetric flow characteristic was found in both the flame and the smoke plume zone. In the flame region, the flame morphology in terms of the tilt angle is a good parameter indicating the asymmetric flow characteristic. In general, the tilt angle of the small fire is larger than that of the big fire. The tilt angle of the small fire decreases while that of the big fire increases until equaling to each other under the HRR ratio reaching unity. In the smoke plume region, the smoke plumes from the small and the big fire will converge at a certain height with some shifting distance, which is another parameter indicating the asymmetric flow characteristic. Besides, the smoke plume merging process driven by asymmetric air entrainment can be divided into three stages, namely the I) Separate stage, II) Converging stage and III) Complete coalescence stage. Correlations of the converging & coalescence height suggesting the starting point of the II and III stages were proposed.