A numerical study of the low-temperature zone in tunnel fires with strong longitudinal ventilation

In this paper, a numerical study was conducted to study the low-temperature zone induced by the strong longitudinal ventilation in tunnel fires by using Fire Dynamics Simulator (FDS). Six different longitudinal ventilation velocities at a range of 2m/s to 6m/s, two different heat release rates (5MW and 8MW) and two tunnel widths (5m and 10m) were considered in the simulations. Results showed that the bifurcation flow formed with the increasing of longitudinal velocity, and there would be a low-temperature zone. The low-temperature zone, results from comprehensive effect of inertia force and thermal buoyancy, expands with the enhancement of longitudinal ventilation. A prediction model was proposed and it revealed that the length of low-temperature zone is in proportion to the -0.44 power of Q*/V*³. (paper)