## 3 Results
### Comparison of the Smoke Distribution in Different Sides of the Tunnel
#### 3.2.1 Temperature  
In previous studies, the fire source location has predominantly been assumed to be at the centerline of the tunnel, resulting in symmetrical horizontal and longitudinal temperature distributions. However, considering real scenarios, when a vehicle catches fire in a tunnel, it is more likely that the fire source vehicle will be positioned on one side of the tunnel.  
Figure 5 shows the longitudinal temperature distribution at the characteristic height for the critical velocity group at 360 s. In this scenario, the rapid rise in temperature within the fire source area is attributed to the generation of high-temperature flames and smoke. This phenomenon is represented by the initial peak on the temperature distribution figure at the inner side of the tunnel. Subsequently, propelled by longitudinal ventilation, the high-temperature smoke propagates forward. However, because of the bending of the tunnel, it collides with and rebounds off the outer wall, resulting in a distinct peak region on its surface. The variation in the curvature of the tunnel leads to the difference in the location of the outer side temperature peak. Consequently, multiple peaks are observed as the high-temperature smoke repeatedly interacts between the inner and outer sides. As one moves away from the fire source, the fluctuations in temperature in the centerline of the tunnel become smaller and gradually downward. The location and height of the temperature peak of Group A (tests 4, 6, 8, and 10) significantly differ from those observed in the straight tunnel (test 2). This discrepancy can be attributed to the influence of the curved tunnel on the initial impact position of high-temperature smoke flow under longitudinal ventilation conditions, resulting in variations in the subsequent temperature distributions.  
Figure 5: Variation in longitudinal temperature at the characteristic height of the critical velocity group. (**a**) Comparison of temperature on different sides of the tunnel for Group A. (**b**) Comparison of temperature on different sides of the tunnel for Group B.  
For Group B (tests 12, 14, 16, and 18), the longitudinal temperature distribution on the tunnel's inner side, outer side, and centerline closely resembles that of the straight tunnel (test 2). However, notable disparities arise in terms of peak temperature values between the inner side and outer side of the tunnel at the corresponding distance from the fire source. The numerical comparisons reveal significant differences in both the temperature distribution and peak temperatures between the tunnel curvature radius of 1000 m and 1200 m with a straight tunnel. Conversely, when the tunnel curvature radius is set as 1500 m and 2000 m, the temperature distribution and peak temperatures are relatively the same as those observed in the straight tunnel.  
However, when the tunnel ventilation velocity is below the critical velocity, the longitudinal temperature distribution exhibits distinct variations, as shown in Figure 6. Under such circumstances, the driving force of longitudinal ventilation for high-temperature smoke within the tunnel becomes insufficient, resulting in its predominant distribution along the longitudinal ventilation of the tunnel. Nevertheless, the curved wall still exerts a certain inhibitory effect on smoke spread. This is primarily manifested by a consistent temperature distribution along the centerline of the tunnel in different simulations without significant differences observed. The primary distinction between the inner and outer sides of the tunnel lies in the maximum temperature within the core area of the fire source. However, beyond this core area, the smoke enters a one-dimensional longitudinal propagation stage.