Numerical study on smoke temperature characteristics in T-shaped bifurcated tunnel fires

Due to the swift progress of subterranean urban transportation, various branching structures emerged one after another. When it brought significant convenience to people’s travel, the fire hazard associated with it could not be overlooked. This paper analyzed the impact of the T-shaped bifurcated structure on the temperature characteristics of fire smoke through fire dynamics simulator (FDS) numerical simulation. The findings revealed that the temperature decrease trend of each section below the ceiling in a T-shaped bifurcated tunnel could be accurately described by a double exponential model. Notably, the attenuation coefficient of each section basically remained unchanged under natural ventilation. However, the coefficient varied distinctly and directly related to the dimensionless ventilation velocities (V') in each section under longitudinal ventilation. The maximum fire smoke temperature below the tunnel ceiling of the T-shaped bifurcated tunnel was higher than that below the single tunnel ceiling at lower ventilation velocities (V' ≤ 0.19), while lower than that below the single tunnel ceiling at higher ventilation velocities (V' > 0.19). On the basis of the numerical simulation data, a predictive model to estimate the maximum fire smoke temperature rise below the tunnel ceiling of a T-shaped bifurcated tunnel was proposed.