Investigation of smoke bifurcation flow has been receiving more attentions, however, delicate quantitative analyses on different regions of the bifurcation flow have rarely been addressed. In this study, a series of small‐scale experiments were conducted to investigate smoke bifurcation flow in longitudinal ventilated tunnels. Results show that when longitudinal ventilation velocity increases to a certain value, the smoke bifurcation phenomenon emerges, and a low‐temperature region forms in the center of the tunnel. Similar to the natural conditions, smoke development under relatively strong ventilation can also be subdivided into four regions. With the increase of ventilation velocity, the ceiling impact region, side wall impact region, and convergence region of two smoke streams move further downstream, indicating that the bifurcation phenomenon becomes more evident. A simple model is proposed based on theoretical analysis and experimental phenomenon to predict two characteristic lengths of smoke bifurcation flow: the offset distance of ceiling impact region and the length of low‐temperature region. Both characteristic lengths increase with ventilation velocity and can be well correlated with the dimensionless ventilation velocity defined in Equation (2) ( V^′). The results of this work could provide references for both tunnel ventilation designers and fire science researchers.

中文翻译：

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纵向通风隧道火灾烟气分叉流的实验研究

烟气分叉流的研究已受到越来越多的关注，但是，很少对分叉流的不同区域进行精细的定量分析。在这项研究中，进行了一系列的小规模实验，以研究纵向通风隧道中的烟气分叉流。结果表明，当纵向通风速度增加到一定值时，会出现烟气分叉现象，并在隧道中心形成低温区域。与自然条件类似，在相对较强的通风条件下产生的烟雾也可以分为四个区域。随着通风速度的增加，两条烟流的天花板冲击区域，侧壁冲击区域和会聚区域向下游移动，这表明分叉现象变得更加明显。在理论分析和实验现象的基础上，提出了一个简单的模型来预测烟支流的两个特征长度：顶棚冲击区的偏移距离和低温区的长度。两种特征长度都随通风速度而增加，并且可以与公式（2）中定义的无量纲通风速度很好地相关（ V ^′）。这项工作的结果可以为隧道通风设计人员和消防科学研究人员提供参考。