Effect of longitudinal slope on the smoke propagation and ceiling temperature characterization in sloping tunnel fires under natural ventilation

In order to reduce risk and increase resilience of transportation tunnels, the early-phase detection and protection of fire are of great significance for the safety assessment of tunnel. In this work, numerical simulations are conducted to characterize the thermal plume propagation and ceiling temperature profile in a tunnel with longitudinal slope increasing from 0% to 15%. For the sloping tunnel, as there exists elevation difference between the tunnel ends, the longitudinal air flow will be induced from the lower end. Under such circumstances, the stack effect occurs and it becomes the primary driving force for the smoke movement in tunnel. Results show that the thermal plume behaviors in the sloping tunnel, including the thermal flow field and the temperature profile, show apparently different from those in the horizontal one. The induced air flow rate that directly related to the strength of stack effect is quantified, and on this basis, the predictive correlation of the temperature profile under the ceiling is proposed by considering the influence of the stack effect for different tunnel slopes. Besides, the accuracy and applicability of the obtained correlation are further verified by comparing to a total of four series of previous experimental data with a wider range of tunnel slopes, dimensions, and heat release rates.

Automated summary

This study investigates the influence of stack effect on smoke movement in sloping tunnels. Numerical simulations reveal that the thermal plume characteristics in sloping tunnels are different from those in horizontal tunnels. The strength of the stack effect is quantified by the induced air flow rate, and a predictive model for the temperature profile is proposed.