Experimental Study of the Flow Structure in Fire-Induced Whirlwinds Downwind of a Fire Using Particle Image Velocimetry

The flow structure of fire-induced whirlwinds that occur downwind of a 90-cm-diameter methanol flame was investigated using particle image velocimetry (PIV) and a flow visualization technique. The PIV images showed that the whirlwinds occurred as counter-rotating vortices on both sides of a reverse flow downwind of the flame that moved toward it near the floor. The whirlwinds started near the floor and extended upwards, with a lower tangential velocity near the floor. The radius of the forced vortex region in the whirlwinds increased above a height of 11 cm. Whirlwinds downwind of the 90-cm-diameter methanol flame behaved the same as whirlwinds downwind of a 3-cm-diameter flame that were investigated in a previous study.