Despite widespread recognition that confluences are characterized by complex hydrodynamic conditions, few studies have mapped in detail spatial patterns of flow at confluences and variation in these patterns over time. Recent developments in large-scale particle image velocimetry (LSPIV) have created novel opportunities to explore the spatial and temporal dynamics of flow patterns at confluences. This study uses LSPIV to map two-dimensional flow structure at the water surface at a confluence and to examine variation in this structure over time. Results show that flow within the confluence is characterized by a large region of flow stagnation at the junction apex, a region of low velocities at the downstream junction corner, and a region of merging of the two flows along a mixing interface within the center of the confluence. Interaction between the incoming flows varies over time in the form of episodic pulsing in which one of the two tributary flows first decelerates and then subsequently accelerates into the confluence. The cause of this pulsing remains uncertain, but it may reflect unsteadiness in the water-surface pressure-gradient field as the two flows compete for space within the confluence. No large-scale vortices are evident within the mixing interface for the particular flow conditions documented in this study, but such vortices do occur along the margins of the stagnation zone where shearing action between fast-moving and slow-moving fluid is strong. The results of the study provide insight into the time-dependent dynamics of the spatial structure of flow at stream confluences.

中文翻译：

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大规模粒子图像测速法揭示了流汇合处流入流的脉动

尽管人们普遍认识到汇合处具有复杂的流体动力学条件，但很少有研究详细绘制汇合处流动的空间模式以及这些模式随时间的变化。大规模粒子图像测速 (LSPIV) 的最新发展为探索汇合处流动模式的空间和时间动态创造了新的机会。本研究使用 LSPIV 绘制汇合处水面的二维流动结构，并检查该结构随时间的变化。结果表明，汇合处流动的特点是在交汇处顶点有一个大的流动停滞区，在下游交汇处拐角处有一个低速区，以及在汇合处中心内沿着混合界面的两个流动的合并区域。合流。传入流之间的相互作用以偶发脉冲的形式随时间变化，其中两个支流之一首先减速，然后加速进入汇合处。这种脉动的原因仍然不确定，但它可能反映了水面压力梯度场的不稳定性，因为两种水流在汇合处争夺空间。对于本研究中记录的特定流动条件，混合界面内没有明显的大规模涡流，但这种涡流确实发生在快速移动和缓慢移动的流体之间的剪切作用很强的停滞区边缘。研究结果提供了对河流汇合处流动空间结构的时间相关动态的洞察。