Numerical Study of Smoke Distribution in Inclined Tunnel Fire Ventilation Modes Considering Traffic Conditions

Japan and Europe have adopted significantly different ventilation modes with regard to traffic conditions (with or without congestion). This study focuses on the smoke behavior of different ventilation modes by conducting a 3D CFD analysis of smoke distribution and CO concentration variation and then comparing these modes based on two groups (relatively low target velocity: 0 and 1 m/s; relatively high target velocity: 2 and 3 m/s). The considered fire size is 30 MW for four longitudinal gradients (0, 2, 4, and 6%). In the simulation results, velocities of both 0 and 1 m/s reveal good performance in maintaining the stratification of smoke and ensuring the safety of the environment in 10 min in the occurrence of traffic jams. However, in 15 min, the smoke conditions change. Thus, it is difficult to distinguish which ventilation mode (0 and 1 m/s) shows relatively better performance during traffic congestion. When traffic is uncongested, the comparison of Um = 2 and 3 m/s reveals that a target velocity of Um = 2 m/s (lower than critical velocity) can also prevent the risk of smoke on the upstream side because no descending phenomenon is observed. Moreover, Um = 2 m/s causes the relatively slow propagation of descending smoke, increasing the possibility of evacuation once a second traffic incident occurs on the downstream side of the fire source.

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