Numerical studies on fire whirls in a vertical shaft

Fire whirls commonly generated in urban and wildland fires might be found in vertical shafts for tall buildings. Internal fire whirls have to be studied in the ventilation duct of green buildings. It is very dangerous for fire fighters nearby them and will cause extensive damage. An external source of angular momentum is required to produce buoyant whirls with large swirl velocity components while entraining air to the fire. To understand the generation mechanism and structure of a plume-driven fire whirl, a room-scale vertical square channel was constructed in a large room. Numerical studies of buoyant fire whirls will be presented in this study with Computational Fluid Dynamics (CFD). Numerical results predicted by CFD indicated that no obvious rotation as in experiment was observed in the vertical square channel. Fire whirl can be induced easily in two symmetric corner gaps. The analysis results indicated that angular velocity component distributions predicted by CFD were similar to that of the Burgers vortex, and axial velocity component distributions were similar to that of the Sullivan vortex. Both experimental and numerical results indicated that rotation and rotation intensity were affected by width of corner gap.