Influence mechanism of longitudinal ventilation and bifurcation angle on tunnel fire temperature distribution and smoke diffusion.

This article focuses on the experimental and numerical investigation of smoke temperature characteristics and flow behavior in underground bifurcated tunnels under longitudinal ventilation during fire scenarios. Using a 1:20 scale tunnel model with adjustable bifurcation angles (30° to 90°), the study examines how ventilation speed and bifurcation angle affect the maximum ceiling temperature rise and longitudinal temperature decay distribution. The research establishes predictive models that incorporate the effects of longitudinal ventilation and bifurcation angle on temperature rise, showing that airflow partially enters the branch tunnel and that vortices form at smaller angles, influencing smoke spread and evacuation. The models demonstrate good agreement with experimental data, with errors within 20%, providing valuable references for fire safety design and evacuation planning in complex underground tunnel networks.