## 3 Results
### Impact of Opening Sizes
#### 3.1.2 Results for Building Models with Varying Leeward Opening Sizes  
Figures 15 and 16 illustrated the velocity and pressure contour distributions for gable roof buildings with fixed inlet opening and variable outlet opening sizes. According to the results obtained, the increase in the exit opening size directly affected the air velocity inside the building; in other words, as the exit opening size enlarged, the air velocity within the building increased. In the LO5 building model, which had a larger outlet opening size than the other models, the airflow entering the interior travelled at a higher velocity and left the building model without any sudden drop in velocity. This demonstrated that the airflow can be more easily discharged through the larger outlet opening, resulting in a smoother and faster flow profile within the building model. Besides, a rapid drop in air velocity occurred in building model LO1 with a smaller outlet opening. This sudden drop in air velocity limited the volume of air passing through the opening and caused the airflow to collect within the building. The accumulation of air inside caused a pressure increase directly inside the building and around the opening. The increased pressure affected the ventilation process by forcing the air out through the outlet opening. This explained why model LO1, which had a smaller opening size, had the maximum velocity at the exit point and the minimum velocity at the entry point. Consequently, in the LO1 model, the internal pressure reaches its highest value while the lowest velocity values are achieved. In contrast, the LO5 model exhibits the lowest pressure and the highest velocity values. These findings demonstrate that the size of outlet opening plays a decisive role in the airflow velocity and pressure distribution inside the building and that wider openings increase the indoor air velocity while decreasing the pressure. Figure 15: Dimensionless velocity distributions of buildings with different leeward opening configurations. (**a**) LO1, (**b**) LO2, (**c**) LO3, (**d**) LO4, (**e**) LO5. Figure 17 presents the distribution of streamlines for building models with different outlet opening sizes. Upon examining the results, it is evident that a horseshoe vortex forms in the front lower part of all building models, regardless of changes in outlet opening dimensions. In each model, a counterclockwise flow motion occurs above the incoming jet, whereas in the LO5 model, an opposite flow direction is observed. This reverse flow direction may be interpreted as the large outlet opening makes the flow inside the building freer and reduces turbulence in the interior. Additionally, the center of the recirculation region formed behind the building moves farther from the building as the outlet opening size increases. This effect is particularly noticeable in the LO5 model; in this model with a larger opening size, the recirculation region forms farther from the building. This finding indicates that the outlet opening size exerts a direct influence on the flow structure at the rear of the building. Figure 16: Pressure coefficient distributions of buildings with different leeward opening configurations. (**a**) LO1, (**b**) LO2, (**c**) LO3, (**d**) LO4, (**e**) LO5. Figure 17: Streamline distributions of buildings with different leeward opening configurations. (**a**) LO1, (**b**) LO2, (**c**) LO3, (**d**) LO4, (**e**) LO5. Figure 18 shows the change in U/U\({}_{\text{ref}}\) along the horizontal line for five different models with a fixed inlet opening. Although the inlet opening was kept constant for all models, the normalized velocity values differ significantly. At x/D = 0, the U/U\({}_{\text{ref}}\) value for LO1 is 0.202524, while for LO5 it reaches 0.833925. This indicates that an increase in the outlet opening not only affects the outlet performance but also influences the inlet flow through the pressure distribution within the internal space.