Numerical simulation on the maximum temperature and smoke back-layering length in a tilted tunnel under natural ventilation

Abstract

The present study investigates the maximum temperature and smoke back-layering length S in the downhill direction from the fire source in a tilted tunnel under natural ventilation. Numerical simulations were conducted using FDS to study the smoke flow behaviors for a fire in a tunnel with nine tunnel slopes of 0, 1%, 2%, 3%, 4%, 5%, 6%, 7% and 8%. It was found that, due to the stack effect, the smoke stagnated at a distance from the fire source in the downhill direction. The effects of tunnel slope,  , fire source heat release rate, Q , source-ceiling height H and tunnel width W on the maximum temperature and smoke back-layering length were studied. Results showed that the maximum temperature under the ceiling decreased with the increasing of tunnel slope or the decreasing of tunnel width. However, it increased with the increasing of heat release rate or the decreasing of source-ceiling height. A model was proposed for the maximum temperature rise. The smoke back-layering length S decreased with the increasing of the tunnel slope. Fire source heat release rate and tunnel width had no significant effect on the smoke back-layering length. And the smoke back-layering length decreased with the decreasing of source-ceiling height. Based on dimensional analysis, a simple model including the effects of both the tunnel slope and source-ceiling height H, was proposed to predict the smoke back-layering length.

A simplified calculation method on the smoke back-layering length and inlet air velocity in a tilted tunnel fire without shaft

“…Zhang et al 23 carried out the numerical simulation under natural smoke exhaust system without the vertical shaft in a tilted tunnel and proposed an expression of the smoke back-layering length as equation (2)where S is the smoke back-layering length (m). α is the tunnel slope (%).…”

“…Wan et al 22 proposed a model of the inlet air velocity of fires in an inclined tunnel under natural ventilation with a vertical shaft by dimensional analysis and numerical study. Zhang et al 23 conducted numerical simulation and dimensional analysis to establish a model of the smoke back-layering length that is independent of the heat release rate. Kong et al 24 carried out numerical simulations and theoretical analysis to analyze the effect of the different longitudinal fire locations on smoke behaviour characteristics caused by fires in inclined tunnels.…”

A study on the temperature profile of bifurcation tunnel fire under natural ventilation

“…For example, Alpert [ 8 ] and Kurioka et al [ 9 ] developed maximum temperature prediction models for a tunnel fire. Moreover, researchers have carried out studies on the factors affecting the maximum temperature, such as the location and number of fire sources [ 10 – 12 ], the shape of tunnel cross-section [ 13 , 14 ], velocity of longitudinal ventilation [ 15 ], vehicle blockage in a tunnel [ 16 , 17 ], ambient pressure [ 18 , 19 ], and the slope of the vertical shaft [ 20 ]. In addition to the maximum temperature, researchers have also investigated temperature decay.…”

Investigation of the Temperature Beneath Curved Tunnel Ceilings Induced by Fires with Natural Ventilation

“…In addition, it has been shown in previous studies that the temperature in a tunnel fire can be affected by various aspects, such as the tunnel geometry, inclination, location of fires, ventilation conditions, vehicle blockage, etc. [11][12][13][14][15][16].…”

“…Zhang et al [13] revealed that the maximum temperature below the tunnel ceiling varies with the tunnel slope. Their results showed that an increase in the tunnel slope decreases the maximum temperature.…”