An Experimental Analysis of Flame Deflection Angles Under Sidewall Smoke Extraction in Immersed Tunnel Fires

This study systematically investigates the variation in the ceiling flame tilt angle in an immersed tube tunnel under the combined effect of longitudinal ventilation and sidewall smoke extraction. The experimental program considers different longitudinal velocities, various sidewall smoke exhaust rates and multiple relative distances between the fire source and the sidewall exhaust outlet, aiming to comprehensively reveal the flame tilt angle under multi-factor coupling conditions. Experiments were carried out in a reduced-scale tunnel model (6.64 m long, 0.96 m wide and 0.5 m high). A porous gas burner supplied a steady heat release, with its distance from the sidewall exhaust outlet systematically varied. Results indicate that the flame tilt angle decreases as the distance between the fire source and the sidewall exhaust outlet increases. A theoretical model was developed to predict the flame tilt angle by incorporating both the sidewall smoke exhaust rate and the relative fire source–exhaust distance. The model accounts for mass loss due to smoke extraction, estimated from the local longitudinal velocity distribution. Predictions from the proposed model agree well with the experimental data.