Impact of location of jet fan on airflow structure in tunnel fire

► Upstream airflow structure inside tunnel varies with the nature of fuel. ► Orientation of the fire site affects the temperature distribution. ► Airflow structure at downstream is insensitive to magnitude of upstream velocity. ► The expected longitudinal airflow may fail to prevent backlayering. Airflow structure and its magnitude are important for smoke management in longitudinally ventilated tunnels. This paper presents a sensitivity study by Computational Fluid Dynamics technique, which considers different dimensions, orientations and the natures of fire source. Its impact on the airflow velocity and temperature distribution is investigated with various locations of fan group activated. A theoretical correlation between the distance of active fan group from the fire source and the upstream velocity is proposed individually for pool fire and solid fire. It reveals that the nature of the fire source imposes adverse effect on the upstream air velocity and the airstream pattern over the entire tunnel. The upstream velocity remains fairly constant when the active fan group is located 200 m or beyond from a vehicle fire that occupies a significant cross-sectional area of tunnel.