## 3 Results and Discussions
### Optimization of the Smoke Control System  
The above study showed that the external wind had an impact on the characteristics of smoke concentration distribution under the TSE system. The smoke in the station hall diffused longitudinally to the B-end due to the SSE wind. The smoke spread to passageway D due to the SW wind's rapid speed, while the N wind had less of an impact. To solve the problem of the TSE system not being able to effectively control the smoke caused by the external wind, an OSC system with smoke barriers was proposed to implement the zoning control scheme in this study.  
As shown in Figure 14, smoke barriers (0.5 m) were added to the passageways [24]. A central smoke barrier with a height of 1 m was installed on the middle ceiling of the station hall to divide the station hall into two smoke-control zones. To imitate the smoke control effect with the optimization measures, the least favorable conditions (Cases 5, 10, and 15) for each wind direction were selected as the control group. As shown in Table 6, the optimized working conditions were set as Cases 16, 17, and 18.  
Figure 15 demonstrates how the three wind directions in Zone II effectively controlled the smoke. Figure 16 displays the characteristics of the CO\({}_{2}\) concentration distribution for the TSE and OSC systems under the three wind directions. Figure 16a illustrates how the smoke diffusion degree in Case 16 was significantly lower than that in Case 5. Compared to Case 10, the smoke diffusion degree in Case 16 decreased slightly, as shown in Figure 16b. This was mostly owing to the sudden change in smoke concentration caused by the intervention of the central smoke barrier, which effectively prevented smoke from spreading to Zone I. However, the peak value of the CO\({}_{2}\) concentration increased in the cases of the OSC system, owing to the accumulation of smoke above the fire source.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Case**} & **External Wind** & **External Wind Speed** & **Optimization Measure** \\  & **Direction** & **(m/s)** & **Simoke barriers were installed in all \\ \hline
16 & SSE & 5 & Smoke barriers were installed in all \\
17 & N & 5 & passageways and in the middle of the \\
18 & SW & 5 & station hall \\ \hline \hline \end{tabular}
\end{table}
Table 6: Optimized simulation conditions.  
Figure 14: Schematic of the station hall with smoke barriers.  
Figure 16: _Cont._  
Figure 15: Smoke concentration distribution contours in the station hall under the OSC system.  
were decreased by 21.74 m, 5.22 m, and 0.87 m, which correspond to differences of 35.45%, 13.64%, and 2.35%, respectively.  
Adding smoke barriers to further divide the smoke control zones could effectively cope with the adverse impact of external wind on the TSE system in the station hall. The results showed that the smoke barrier in the passageways could prevent smoke from spreading to the passageways and outside air from flowing into the station hall, which lessened the impact of external wind on the smoke extraction in the station hall. The central smoke barriers had a specific impact on longitudinal diffusion, which effectively prevented the spread of smoke to the non-fire region and made it possible to evacuate safely.