## 3 Results and Discussions  
### Effect of Exhaust Vent Position  
The position of the exhaust vent may influence the ventilation performance. Figure 4 shows the four different arrangements of the exhaust vent. The six holes in the model represent the chimneys. The arrangement effect on the ventilation efficiency was analyzed by the density of the high-temperature streamlines in the cabin. When the number of streamlines in the cabin is constant, more red-yellow traces in streamline density indicate a larger proportion of high-temperature components in the cabin, longer vortex time in the nacelle, and more unreasonable airflow organization. Figure 5 manifests the analysis results of the streamline density.  
As can be seen in Figure 5, the high-temperature traces of the arrangements in Figure 4a,c are significantly less than those of the arrangements in Figure 4b,d. In Figure 4a, the side-setting of the exhaust vents is not conducive to the smooth discharge of the cooling airflow; the airflow stays in the cabin for a long time, resulting in significant accumulation of heated gas. It should be emphasized that Figure 5 only provides the cloud and streamline maps of high temperature (>55 \({}^{\circ}\)C), i.e., the cloud map only displays the temperature volumes above 55 \({}^{\circ}\)C, while the streamline map only displays the temperature streamlines above 55 \({}^{\circ}\)C.  
Figure 4: Four different arrangements of the exhaust vent: (**a**) left side arrangement, (**b**) left-right sides arrangement, (**c**) left-side and left-roof arrangement, and (**d**) left-side and right-roof arrangement.  
Figure 5: _Cont_.  
The cloud map (temperature volume \(>\) 55 \({}^{\circ}\)C) in each arrangement is compared in Figure 6. The temperature volumes above 55 \({}^{\circ}\)C in arrangements in Figure 4a,c are significantly smaller than those in arrangements in Figure 4b,d, which indicates that if the distance between the exhaust vent and the air inlet increases, the venting time of high-temperature airflow may increase. In arrangement (a), there were two exhaust vents arranged on the two sides of the cabin. The exhaust went through two sides of the cabin, so that the high-temperature volumes were slightly smaller than that in arrangement (c); however, compared with arrangement (c), the venting time in arrangement (a) was longer.  
In addition, Figure 6 shows the pressure ratio between the air outlet and the exhaust vent. The pressure ratios in arrangements in Figure 4c,d increase by more than 3% when comparing with those in arrangements in Figure 4a,b, which shows that the arrangement of the exhaust vent on the cabin roof is more effective than that at the two sides with respect to ventilation performance [16]. This is because the airflow resistance [19] is significantly reduced during the cooling process if placing the exhaust vent on the cabin roof so that the high-temperature gas can be discharged effectively. As a result, arrangement (c) is more reasonable than the others.  
Figure 5: Cloud and streamline maps of the high-temperature distributions (\(>\)55 \({}^{\circ}\)C). Volume sizes of the four arrangements are: (**a**) 589.1 m\({}^{3}\), (**b**) 645.3 m\({}^{3}\), (**c**) 418.7 m\({}^{3}\), and (**d**) 593.9 m\({}^{3}\).