# Influence of Eddy-Generation Mechanism on the Characteristic of On-Source Fire Whirl
## 4 Conclusions  
A numerical simulation of a unique combustion process occurring in an enclosed configuration with one or two side entrainment slit(s) was performed to assess the character of a fire whirl formulated by means of various eddy-generation mechanisms. The numerical framework of the proposed model consists of the WALE large eddy simulation turbulence model coupled with reduced detailed chemistry to describe the intricate whirling flaming flow behaviour. The numerical model adopts a uniformed \begin{table}
\begin{tabular}{c c c} \hline \hline \multirow{2}{*}{**HAB (m)**} & \multicolumn{2}{c}{**Mean Vortex Core Radius (cm)**} \\ \cline{2-3}  & **01 Slit** & **02 Slit** \\ \hline
0.1 & 3.13 & 3.01 \\
0.3 & 2.33 & 3.13 \\
0.5 & 5.52 & 2.33 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Mean vortex core radius at three monitoring HABs: 01 slit case and 02 slit case. Figure 16: Plot of tangential velocity along with the radial direction at three monitoring HABs: 01 slit case (**a**), and 02 slit case (**b**). structured discretisation scheme, a fixed fuel injection rate, and a soot-free alcohol-based parent fuel, to isolate and constrain the complicated coupling effect between the combustion process and the flow dynamics. The numerical simulation of the baseline model consists of one flow channelling slit, replicating the test rig layout in the literature. This was firstly validated against experimental data and achieved satisfactory agreement. A modified model built with the introduction of an additional slit was subsequently constructed, and the results generated were compared with the baseline for assessment. The analysis concluded that, with the intensified eddy-generation mechanism,  
* The peak flame temperature of the formulated fire whirl increased by 9.42%, from 1380 K to 1510 K;
* The visible flame height increased by 84.38%, from 0.32 m to 0.59 m;
* The axial velocity and the axial velocity dominant region increased by 6.81% and by 46.14%, respectively;
* The flame structure was well-maintained as the temperature core radius remained relatively unchanged at all monitoring HABs, compared with the increase by 153.33% in the baseline case;
* The circulation core structure was well-sustained, and the mean vortex core radius was observed to be nearly identical at the elevated height of up to 0.5 m, whereas there was an increase of 136.91% in the baseline case. In summary, the results generated from this numerical study demonstrate that the addition of an introduced slit intensifies the circulation, enhances the mixing of the oxidiser with the reactants, and hence facilitates the ensuing combustion process. As a result, the numerical model with stronger eddy-generation mechanisms, i.e., featuring two flow channelling slits, formulates and sustains a fire whirl possessing an elongated, constrained and swirling combustion region, compared with those generated from the single-slit configuration. In addition, this numerical study showcases the capability of the proposed numerical framework to capture various features of the whirling reacting flow, which are often difficult to acquire and assess by experimental means. The model also provides visualised information on the combustion process and flow field, thus delivering theoretical insight. The numerical model presented in this study, is therefore proved to be a feasible tool for assisting the understanding of the fundamentals of the formation and evolution of this intriguing combustion phenomenon. Conceptualization, A.C.Y.Y., Q.N.C., S.K. and G.H.Y. ; Data curation, C.W. and H.L.Y. ; Formal analysis, C.W., T.B.Y.C., R.C. and H.L.Y. ; Funding acquisition, A.C.Y.Y. and G.H.Y. ; Methodology, A.C.Y.Y., Q.N.C., S.K. and G.H.Y. ; Resources, S.K. ; Supervision, A.C.Y.Y., Q.N.C., S.K. and G.H.Y. ; Validation, Q.C. ; Visualization, Q.C. ; Writing--original draft, C.W. ; Writing--review & editing, T.B.Y.C. and R.C.