Exploring Temperature Variation Patterns at the Apex of Asymmetric V-Slope Tunnels: Unraveling Synergistic Influences of Side Smoke Exhaust and Air Curtain Mechanisms

With the continuous advancement of China's transportation infrastructure, numerous tunnels have been constructed through mountainous regions and across rivers and streams, predominantly exhibiting a V-shaped profile. These tunnels, while addressing practical needs, present substantial risks in the event of a fire, compounded by factors such as the chimney effect. This study utilizes the FDS model to examine the impacts of lateral smoke extraction air velocity, air curtain flow rate, and air supply angle on both the maximum temperature at the apex of V-shaped tunnels and the behavior of smoke propagation. The findings indicate that lateral smoke extraction systems effectively mitigate smoke spread on the non-fire slope and reduce the maximum temperature at the tunnel's summit. However, it was observed that at a slope of 1/3%, smoke consistently spreads across varying slopes towards the non-fire side, irrespective of side exhaust velocity or fire intensity. Conversely, at slopes exceeding 1%, smoke remains confined to the fire side and does not cross the slope point to the non-fire side. Based on the results, a predictive model for the maximum temperature at the tunnel's apex under the influence of side smoke exhaust is proposed, thereby advancing theoretical understanding of V-shaped tunnels. To address the challenge of long-distance smoke spread on low gradients, this study introduces the concept of air curtains within V-shaped slope tunnels. Results demonstrate that air curtains not only effectively limit smoke propagation on the non-fire slope but also lower temperatures at the apex on the fire side. Optimal conditions are identified with a lateral smoke extraction velocity of 6 m/s, an air curtain supply velocity of 3 m/s, and an air supply angle of 30°, which collectively enhance safety for evacuation, facilitate fire rescue operations, and protect tunnel structural integrity.