Study of Temperature Distribution in U-Shaped Underwater Tunnel Fires Under the Influence of Induced Airflow

Compared to a single horizontal or inclined tunnel, a U-shaped underwater tunnel combines both types. If such tunnels catch fire, the resulting scenarios will lead to varying intensities of induced airflow, which significantly impact the internal heat transfer mechanisms. This study numerically simulated the effects of varying induced airflow strengths on the heat transfer proportion and temperature distribution within the tunnel. Key variables including the inclination angle of tunnel sections, the heat release rate (HRR) of the fire source, and its distance to the tunnel opening were systematically investigated. The results indicate that when the fire is in the horizontal tunnel section, the primary factor affecting the temperature field distribution is the HRR of the fire. As the fire source moves toward the inclined tunnel section, a transition to strong induced airflow occurs above the corner at low angles of inclination. As the slope increases, the transition position shifts downstream, toward the lower side of the corner. At this point, the tunnel is affected by strong induced airflow. Using dimensionless analysis, models were developed for temperature field distribution under strong and weak induced airflow, guiding underwater tunnel spray activation temperature and firefighting and rescue efforts.