A detailed description is given of double burner fire whirls that are similar in structure to the type of combined whirls seen in nature. The whirls are generated using the fixed frame method, and two burners are placed symmetrically about the center of the fixed frame. The flame from each burner sweeps along the ground until it reaches the point midway between the burners, where the two flames wrap around each other in rotation as they stretch vertically. Stereo Particle Image Velocimetry is used to examine the structure and behavior of the whirls under different burner separation and burning rate conditions. The circulation, Froude number and whirl height for the double burner whirls are found to follow similar scaling relationships to those found for single centered and offset burner whirls, but the velocity profiles display significant differences, including the presence of lobed radial velocity profiles in the core of the combined whirl. The air entrainment contours suggest double whirls may be more effective at entraining, lifting, and ejecting flaming debris.
Hartl, K.A.; Smits, A.J. 2022. The interaction of double burner fire whirls. Combustion and Flame 235:111679. https://doi.org/10.1016/j.combustflame.2021.111679