# CFD Assessment of Car Park Ventilation System in Case of Fire Event
## 3 Results  
This section is dedicated to presenting the study's outcomes. It should be mentioned that the parameter governing convergence is established through the \"residualControl,\" a constituent of the solver settings enabling specification of convergence criteria for various variables (or fields) within the simulation. This mechanism defines the tolerable extent of disparity (residual) between discretized equations and their resolved counterparts. The solver deems the simulation converged and concludes its iterations when residuals for all designated fields dip below stipulated convergence criteria. For this study, the convergence criterion for all parameters (\(p\), \(U\), \(k\), and \(\varepsilon\)) is uniformly set at \(1\times 10^{-6}\), while a consistent time interval of one second is implemented across all simulations. Figure 4 (left) showcases the results of simulations for the base case placement of jet fans. These jet fans are assumed to operate in high-speed mode, generating an outlet air velocity of 22.3 m/s. As illustrated in Figure 4 (right), this design yields satisfactory airflow from the supply to the exhaust points. However, certain areas in zones 1, 3, and 4 experience stagnation points where the airflow nearly ceases, posing a risk of smoke concentration in those regions. It is important to note that all subsequent visualizations represent slices taken at a height of 1.7 m, which is considered the average human height. In order to examine the impact of fire source location, a total of 17 distinct scenarios were investigated. The fire scenarios were determined by starting from the initial location and extending 30 m in all directions. However, due to computational constraints, certain  
Figure 4: Base case jet fan positioning (**left**) and resulting velocity field (**right**). \begin{table}
\begin{tabular}{c c c} \hline \hline  & **Phase 01** & **Phase 02** \\ \hline \multirow{2}{*}{Linear solver} & \(p\): GAMG & \multirow{2}{*}{\(T\): PBiCGStab} \\  & \(U\), \(\varepsilon\), and \(k\): smoothSolver & \\ \multirow{2}{*}{Preconditioner} & \(p\): DIC & \multirow{2}{*}{\(T\): DILU} \\  & \(U\), \(\varepsilon\), and \(k\): DILU & \\ \multirow{2}{*}{Smoother} & GaussSeidel & - \\ \multirow{2}{*}{Application solver} & porousSimpleFoam & scalarTransportFoam \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Configuration of linear solvers, preconditioners, smoothers, and application solvers for Phase 01 and Phase 02.  
fire locations had to be omitted from the study. Figure 5 depicts the 17 selected fire source location scenarios, providing a visual representation of the varied positions considered. To analyze the propagation of smoke and determine the visibility distribution within the car park, the calculator provided in Paraview is utilized to convert the rate of smoke concentration \(\dot{m}_{s}\) to visibility \(S\)[34] using the following formula:  
\[S=K/\alpha_{m}\dot{m}_{s} \tag{9}\]  
where \(K\) is proportionally constant for the visibility for different illumination scenarios as shown in Table 6, and \(\alpha_{m}\) is the specific extinction coefficient for different modes of combustion, as shown in Table 7. Given the presence of illuminated signs in the car park to aid in the evacuation process, a proportional constant of \(K=8\) is applied. Considering the initial stages of a car fire, which primarily involve flaming combustion, it is justifiable to assign an extinction coefficient of \(\alpha_{m}=7875.2\). This post-processing analysis using Paraview's calculator provides a quantitative understanding of how the smoke propagates and affects visibility within the car park. It enables the assessment of potential visibility hazards in different areas, aiding in the identification of high-risk zones and informing appropriate safety measures and evacuation protocols. Figure 6 illustrates the distribution of visibility for the eight worst-case scenarios (i.e., scenarios 2, 4, 7, 9, 11, 13, 14, and 15), presenting a visual representation of how visibility is affected in each scenario.