关键词: 隧道顶部, 障碍物, 烟气密度跃变, 质量卷吸比, 盐水试验

Abstract:

In order to investigate the variation in smoke flow parameters caused by the ceiling barriers and its effects on human evacuation and smoke control system design, brine water experiments were employed to investigate the condition for the occurrence of density jump for the smoke flow downstream of the ceiling barriers and the resulting mass entrainment and smoke layer thickness variation. Results show that the Froude number exceeds one and then drops to be lower than one immediately in the downstream region of the barrier, representing a transition from super-critical to sub-critical flow state, which could be the reason for the occurrence of the density jump of smoke. The smoke density jump leads to the entrainment of fresh air and the smoke layer thickness increase. The height of the ceiling barrier is a crucial parameter influencing the intensity of smoke flow density jump. The ratio of the smoke layer thickness after the density jump and the one before the density jump, the ratio of Froude number before the density jump and one after the density jump and the mass entrainment ratio increase with the increase of dimensionless height of the barrier. When the dimensionless height of the barrier exceeds 0.267, the above three parameters decrease with the increase of the dimensionless height of the barrier. The density jump of smoke flow downstream of the barrier can exceed 0.3, which is larger than the prediction result of the theoretical model.

Key words: tunnel ceiling, barrier, smoke density jump, smoke mass entrainment ratio, brine water experiment