A Study of the Critical Velocity of Smoke Bifurcation Flow in Tunnel with Longitudinal Ventilation

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• 作者：Wei Zhong ; Weike Duanmu ; Tao Wang ; Tianshui Liang
• 关键词：Tunnel fire ; Longitudinal ventilation ; Bifurcation flow ; Critical velocity
• 刊名：Fire Technology
• 出版年：2017
• 出版时间：March 2017
• 年：2017
• 卷：53
• 期：2
• 页码：873-891
• 全文大小：
• 刊物类别：Engineering
• 刊物主题：Civil Engineering; Classical Mechanics; Characterization and Evaluation of Materials; Physics, general;
• 出版者：Springer US
• ISSN：1572-8099
• 卷排序：53

文摘

Small longitudinal velocity cannot prevent backlayering in tunnel fire, while excessive longitudinal velocity will destroy stratification of smoke layer and lead to bifurcation flow. As smoke bifurcation flow proceeds, the longitudinal flow is divided into two streams and flow along both sidewalls of the tunnel ceiling. The critical velocity of bifurcation flow is the minimum value at which bifurcation flow starts to occur. To investigate the critical velocity of bifurcation flow, experiments and CFD simulations were conducted. Experiment was carried out in a reduced-scale tunnel, which is 8 m long, 1 m wide and 0.5 m high. The numerical research was performed using FDS. In simulation, the computational region of a tunnel is 200 m long, 10 m wide. The heat release rate (1 MW to 6 MW) and the height (4 m to 8 m) is changed in the 30 simulation scenarios. Theoretical analysis showed that the dimensionless critical velocity of bifurcation flow only depends on the dimensionless heat release rates, and a mathematical equation is proposed. The reduced-scale experiments indicated that the critical velocity of bifurcation flow is 1.48 times that of critical velocity for preventing backlayering, and the coefficient is in agreement with CFD simulation.