To design a reliable longitudinal ventilation system in a roadway tunnel, it is crucial to know the optimum value of the forced airflow velocity which must be applied to minimize hazards to users trapped in the building during a fire. This optimal value known as the critical longitudinal ventilation velocity, is a crucial criterion for tunnel safety when designing ventilation systems. Analysis of the influence of the fire development location from the tunnel floor on the critical velocity has rarely been studied, although this situation really exists due to the difference in vehicle sizes in practice. CFD simulations were performed in this paper to study this scenario and to estimate the critical velocity for a fire developing in different locations relative to the tunnel floor. The results indicate that as the elevation of the fire location increases from the tunnel floor, the critical velocity decreases. A new model involving the separation distance of the fire location on the tunnel floor and relating the critical velocity to the fire heat release rate is proposed. Furthermore, under critical conditions of ventilation velocity, the results show that the elevation of the fire source location from the floor has a significant effect on the maximum smoke temperature rise below the tunnel ceiling.

为了在巷道隧道中设计可靠的纵向通风系统，了解强制气流速度的最佳值至关重要，必须应用强制气流速度的最佳值，以最大限度地减少火灾期间被困在建筑物中的用户的危险。这个最优值被称为临界纵向通风速度，是设计通风系统时隧道安全的关键标准。分析隧道底板火灾发展位置对临界速度的影响的研究很少，尽管由于实际车辆尺寸的差异，这种情况确实存在。本文进行了 CFD 模拟以研究这种情况并估计在相对于隧道地板的不同位置发生火灾的临界速度。结果表明，随着火灾位置从隧道底板的高度增加，临界速度降低。提出了一种新模型，该模型涉及隧道底板上火灾位置的间隔距离并将临界速度与火灾热释放率相关联。此外，在通风速度临界条件下，结果表明，火源位置距地板的高度对隧道天花板以下的最大烟温升有显着影响。