# Capturing the Swirling Vortex and the Impact of Ventilation Conditions on Small-Scale Fire Whirls
## 5 Conclusions  
In this article, numerical simulations were performed to attempt to thoroughly validate a generic fire field. The generic fire field incorporated all essential physical considerations in fire dynamics, including LES turbulent closure, subgrid-scale combustion with presumed PDF approach, discrete ordinates radiation model, and two-equation soot formation model. To the best of our knowledge, for the first time, the numerical predictions were thoroughly validated against two experimental small-scale fire whirl measurements, where temperature and detailed velocity field were recorded. The predicted temperature profile and velocity field at the vicinity of the vortex core were in good agreement with the experimental results. The presented validation ascertained the capacity and potential of the adopted fire field model in capturing the swirling vortex and dynamic behaviour of fire whirls. Quantitative analyses were carried out based on the validated numerical model. The major findings are summarized as follows:  
1. The centreline temperature variations within the continuous flame are consistent with the empirical correlation by [PERSON] et al. (2018) based on their medium-scale fire whirl measurements.
2. The dimensionless study shows that the tangential velocity within the vortex core follows the fundamental Burgers vortex equation. In the [PERSON] and [PERSON] experiment, the tangential velocities start to increase and deviate from the Burgers equation at approximately three times of the vortex radius, where air entrainment from the ventilation gap is imposed. In the [PERSON] and [PERSON] experiment, the tangential velocities decay rapidly at \(r/r_{c}^{v}\geq 4\) due to the boundary of the two half-cylinders.
3. The development stages of the fire whirls, including the flame rising, fully developed conical fire, and fully developed cylindrical fire stages, are successfully captured by the numerical model.
4. The swirling velocity within the vortex core suppresses the fuel-air mixing and its associated combustion process, causing a noticeable temperature dip at the fire centre. A stronger swirling motion results in a more significant temperature decrease.
5. The air entrainment is crucial in providing imposed circulation for the onset of self-rotating fire whirls. A partially opened ventilation gap significantly weakens the circulation motion, causing insufficient air entrainment within the inflow boundary layer and causing instability to the fire whirl structure. The numerical findings confirm that the strong inflow boundary layer is the key factor affecting the onset of self-rotational motion of fire whirls.  
Data curation, X.F.; Investigation, X.F.; Supervision, A.C.Y.Y., G.H.Y., E.W.M.L. and S.C.P.C.; Writing--original draft, X.F., Writing--review & editing, S.C.P.C. All authors have read and agreed to the published version of the manuscript.  
The financial support provided by the Australian Research Council Industrial Training Transformation Centre (IC170100032) is gratefully acknowledged.  
The authors declare no conflicts of interest.