Study On Flame Characteristics Of Horizontal Turbulent Buoyant Jet On Facade Wall

Fire spill plume and fire attachment often occur in high-rise building fires, which may cause upper fire spread, and thus may induce serious threaten to the safety of human life and property. For understanding building fire spill plume, this study explores the effects of facade wall on the characteristics of horizontal turbulent buoyant jet flame. Fire deflection induced by the entrainment limitation due to facade wall, flame length and temperature distribution is also studied.Using a fireboard as a simulation of a facade wall, we designed a gas burner which can produce different opening sizes and gas velocities. Flame temperature distribution was extracted from the experimental data obtained by a thermocouple array. It is found that the dimensionless temperatures can be approximately correlated to-3/5power of the dimensionless height. Fire deflection of horizontal turbulent buoyant jet is caused by the restriction of flame entrainment due to the presence of a facade wall. We divide the flame spread into two stages:(1) from the opening to the equilibrium point (the position at which the momentum in the horizontal direction decays to zero);(2) fire spread after the equilibrium point with the existing facade (fire deflection or not). It is found that the occurrence of fire attachment mainly depends on the horizontal separation (LE) between the equilibrium point and opening and the flame length. When the ratio of the opening ratio n (n=B/H,B is opening width; H is opening height) is the same, LE increase with the increasing non-dimensional fire release rate. Horizontal turbulent buoyant jet flame length mainly depends on two effects:(1) flame stretching caused by the increase of non-dimensional heat release rate (HRR);(2) flame stretching attributable to the fire entrainment restriction. These two effects are competing.By analysis, the decay of horizontal momentum and fire attachment is mainly attributed to turbulent Reynolds stress. We present an approximate derivation of Reynolds stress term using Prandtl’s mixing length theory, and then by the momentum governing equation, we derive a linear correlation between LE and a modified Fr*is obtained. From that, we can interpret that fire attachment will occur easier when n becomes larger. In terms of the air entrainment limitation extent by facade wall, we divide the flame shape into three types:(1) attached fire;(2) deflected fire with no attachment (2.03<Fr*<4.84);(3) erect fire (4.84<F*<70.4) which means free flame development. When the flame falls into type (2) or type (3), the non-dimensional flame length increases with the increasing modified Fr*.