Experimental study on buoyant flow stratification induced by a fire in a horizontal channel

Experiments were carried out in a reduced-scale horizontal channel to investigate the fire-induced buoyant flow stratification behavior, with the effect of the velocity shear between the hot buoyant flow and the cool air flow considered. This shear intensity was controlled and varied by changing the exhaust rate at the ceiling with one of the end of the channel opened. The flow pattern was visualized by the aid of a laser sheet. The horizontal traveling velocity, vertical temperature profile and stratification interface height of the buoyant flow were measured. The stratification pattern was found to fall into three regimes. Buoyancy force and inertia force, as the two factors that dominate the buoyant flow stratification, were correlated through the Froude number and the Richardson number. At Region I (Ri > 0.9 or Fr < 1.2), the buoyant flow stratification was stable, where a distinct interface existed between the upper smoke layer and the lower air layer. At Region II (0.3 < Ri < 0.9 or 1.2 < Fr < 2.4), the buoyant flow stratification was stable but with interfacial instability. At Range III (Ri < 0.3 or Fr > 2.4), the buoyant flow stratification becomes unstable, with a strong mixing between the buoyant flow and the air flow and then a thickened smoke layer.