Combustion Dynamics of Fire Whirls

Fire whirls are intense, self-sustaining vortices of flame that arise when buoyant hot gases converge and impart rotation to the fire plume. The interplay of vorticity, circulation and buoyant ascent yields a tightly confined column of rapidly burning fuel, characterised by elevated flame temperatures, enhanced mixing rates and extended flame heights. These phenomena range from small laboratory‐scale whirls to vast vortices that accompany urban conflagrations or wildland infernos. The core dynamics involve a balance between axial momentum driven by thermal buoyancy and azimuthal momentum supplied by ambient or induced swirl. Under sufficient rotational strength, vortex breakdown may occur, giving rise to distinct regimes such as the soot-free, laminar blue whirl. Numerical and experimental studies reveal that fire whirls amplify heat‐release rates and modify pollutant formation pathways, making them of both practical interest for efficient burner design and critical concern in fire safety. In wildland contexts, whirls can form suddenly at fire fronts or within canyons, posing a heightened risk to firefighters and infrastructure. Advances in large-eddy simulation and high-speed diagnostics have begun to resolve the multi-scale coupling of turbulence, chemical kinetics and radiative heat transfer that governs inception, stability and transition between regimes. These insights not only inform hazard mitigation strategies but also inspire novel combustion technologies that harness vortex‐stabilised flames for cleaner, more controllable energy release.

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Combustion Dynamics of Fire Whirls publication trend

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Technical terms

Fire whirl: A self-sustaining vertical vortex of flame driven by the convergence of hot gases and ambient air.

Vorticity: A vector measure of the local rotation within a fluid flow.

Circulation: The line integral of velocity around a closed contour, indicating overall rotational strength.

Swirl number: A dimensionless ratio comparing the magnitude of rotational (azimuthal) momentum to axial (buoyant) momentum.

Blue whirl: A soot-free, laminar whirling flame regime arising after vortex breakdown under certain circulation and heat‐release conditions.

Damköhler number: A dimensionless quantity expressing the ratio of chemical reaction timescale to flow (mixing) timescale.

References

1. Review of Vortices in Wildland Fire. Journal of Combustion (2011).
2. Effects of circulation and buoyancy on the transition from a fire whirl to a blue whirl. Physical Review Fluids (2020).
3. Experimental and Numerical Analysis of Formation and Flame Precession of Fire Whirls: A Review. Fire (2021).
4. Large-scale fire whirl and forest fire disasters: Awareness, implications, and the need for developing preventative methods. Frontiers in Mechanical Engineering (2023).
5. Effect of Slope on the Frequency and Height of Fire Whirls. Fire (2023).