Scale model experiments of fire whirls over the non-fuel zone around an L-shaped fire source

The Hifukusho-ato fire whirl (HAFW) is a catastrophic fire accident in Tokyo in 1923 and a representa-tive fire whirl phenomenon that occurs over the non-fuel zone around an L-shaped fire source. Previ-ous studies have mainly focused on fire whirls above fire sources, while very limited work reported the HAFW-type fire whirls, which were found to be scale-dependent (more easily to occur in a large-scale wind tunnel test facility than small-scale ones due to the strong viscous effects in the latter) and thus not precisely discussed. In this study, a scale-independent method is proposed by fitting an additional fire source in the inside bend of an L-shaped fire source to mimic the flame-overhang region observed in the large-scale tests; the HAFW-type fire whirl is then successfully reconstructed in a small-scale test model (1/10,0 0 0th of the HAFW prototype). Meanwhile, the results show that the average fire whirl occurrence position in the flow direction in a large-scale test model (1/2,0 0 0th of the HAFW prototype) does not collapse with those in a small-scale test model (1/10,0 0 0th of the HAFW prototype without additional fire sources installed), but with those in the aforesaid scale-independent test model; such collapse can be summarized by a linear fitting correlation between a normalized fire whirl occurrence position and a modified Froude number under different fire source scales and lateral wind velocities. Based on the above experimental facts, updated scaling law to reproduce HAFW-type fire whirls and similar fire whirl occur-rence positions is provided. This work advances a fundamental understanding of fire whirls generated by an L-shaped fire source; thus, helping guide fire-rescue operations, and benefiting future fire whirl model development. (c) 2021 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Automated summary

This study proposes a scale-independent method to reconstruct the HAFW-type fire whirl in a small-scale test model and provides updated scaling law to reproduce similar fire whirl occurrence positions. The results show a linear correlation between normalized fire whirl occurrence position and modified Froude number under different fire source scales and lateral wind velocities. The findings advance the fundamental understanding of fire whirls generated by an L-shaped fire source and could benefit future fire whirl model development.