Numerical simulation of fire-induced smoke spread characteristics in a one-way downhill multiramp urban tunnel

A full-scale three-dimensional numerical study of fire-induced smoke spread characteristics in a one-way downhill multiramp urban tunnel in Chongqing is proposed. The effects of the tunnel slope and the fire location on the behavior of smoke spread are analyzed. For all six simulated cases, longitudinal ventilation can efficiently preclude smoke from propagating to the mainline tunnel and upstream of Ramp III. The chimney effect caused by the tunnel slope significantly affects the smoke flow in Ramp I and Ramp II. For Case A and Case D, the smoke spreads upstream of Ramp I, and the visibility in Ramp I decreases. The chimney effect reduces the velocity in the entrance of Ramp I by 74.39% and 144.27%, respectively. For Case B and Case E, the smoke spreads upstream of Ramp II, and the visibility in Ramp II decreases. For Case E, the chimney effect reduces the velocity in the entrance of Ramp II from 0.63 m/s to −0.13 m/s.