Experimental characterization of the cold boundary layer surrounding fire whirls

Particle-image velocimetry was employed to investigate the structure of the cold boundary layer surrounding a fire whirl generated in an experimental setup consisting of a pool fire enclosed by distant, inclined vertical vanes that deflect the entraining air. Results obtained for two different vane inclinations were compared with theoretical predictions previously derived using high-Reynolds-number asymptotics. The experiments confirmed the presence of a near-wall region characterized by pronounced inward radial flow, with its magnitude increasing with decreasing radial distance. Under the specific conditions examined, boundary-layer separation and reattachment were observed, giving rise to a long bubble of slow, recirculating flow along the wall. This feature has potential implications for future numerical modeling of fire-whirl structure and dynamics. Novelty and significance An accurate understanding of the flow surrounding fire whirls is necessary to support numerical investigations of their structure and dynamics. Particle-Image Velocimetry (PIV) is applied, for the first time, to obtain an experimental characterization of the cold boundary layer that develops around fire whirls. These novel measurements provide new insights into the structure and morphology of the boundary layer that are not captured by existing theories.