Study of air supplement velocity by thermal stack effect and critical velocity under longitudinal ventilation in the uniclinal V-shaped tunnel

Abstract

This research focuses on the specific uniclinal V-shaped tunnel during a fire, studying the air supplement triggered by the thermal stack effect and further examining the control mechanism of upstream smoke. It revealed how the air supplement velocity generated by the thermal stack effect, influenced by longitudinal ventilation, varied in the tunnel. It also established a prediction model for the critical velocity based on different geometric tunnel parameters. Results indicate that internal longitudinal velocity enhances air entrainment, lowers the temperature field, and significantly reduces the stack effect. As longitudinal velocity increases, the air supplement velocity exhibits an exponential decay, with a decay coefficient identified as 3.22. Higher heat release rates and slope heights increase the internal temperature and height differences, promoting air supplementation. Combining air supplement velocity with the critical velocity prediction for horizontal tunnels, the study quantifies the critical velocity in uniclinal V-shaped tunnels under varying conditions. It introduces a P parameter to decide on the necessity of external mechanical ventilation for smoke control. P ≥ 1 indicates that mechanical ventilation is unnecessary; P < 1 suggests the opposite. These findings offer significant insights into the dynamics of smoke and air in tunnels, providing valuable guidance for tunnel fire smoke management.

Keywords

• Uniclinal V-shaped tunnel fire
• Thermal stack effect
• Air supplement velocity
• Critical velocity