Performance evaluation of longitudinal and transverse ventilation for thermal and smoke control in a looped urban traffic link tunnel

The complex structure of the urban traffic link tunnel (UTLT) exacerbates fire accident risk and increases the difficulty of smoke control, especially for a UTLT with looped tunnel systems. The applicability of the traditional tunnel smoke control methods, e.g., transverse ventilation and longitudinal ventilation, needs further investigation for UTLTs. Experiments were conducted in a small-scale model to investigate the effectiveness of both two ventilation modes for a looped UTLT. In a longitudinally ventilated UTLT, the critical velocities, as the minimal air velocities for preventing smoke infiltrating into the regions upstream of the fire and entering the downstream tunnel branches that are adjacent to the smoke discharge route, should be guaranteed. Multiple operational modes of longitudinal ventilation could be feasible for achieving the desired performance of smoke control. For transverse ventilation, both the effects of the exhaust flow rate and the air supply rate are investigated. To confine the smoke in the tunnel branch where fire occurs, an effective exhaust flow rate could be twice the smoke production rate. Forced air supply could be unnecessary for a UTLT due to the abundance of natural air supply routes. Longitudinal ventilation leads to lower smoke flow temperatures than transverse ventilation does in UTLTs.