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首页> 外文期刊>Earth Surface Processes and Landforms: The journal of the British Geomorphological Research Group >Flow structures at an idealized bifurcation: A numerical experiment
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Flow structures at an idealized bifurcation: A numerical experiment

机译：理想分叉处的流动结构：数值实验

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River bifurcations are key nodes within braided river systems controlling the flow and sediment partitioning and therefore the dynamics of the river braiding process. Recent research has shown that certain geometrical configurations induce instabilities that lead to downstream mid-channel bar formation and the formation of bifurcations. However, we currently have a poor understanding of the flow division process within bifurcations and the flow dynamics in the downstream bifurcates, both of which are needed to understand bifurcation stability. This paper presents results of a numerical sensitivity experiment undertaken using computational fluid dynamics (CFD) with the purpose of understanding the flow dynamics of a series of idealized bifurcations. A geometric sensitivity analysis is undertaken for a range of channel slopes (0.005 to 0.03), bifurcation angles (22° to 42°) and a restricted set of inflow conditions based upon simulating flow through meander bends with different curvature on the flow field dynamics through the bifurcation. The results demonstrate that the overall slope of the bifurcation affects the velocity of flow through the bifurcation and when slope asymmetry is introduced, the flow structures in the bifurcation are modified. In terms of bifurcation evolution the most important observation appears to be that once slope asymmetry is greater than 0.2 the flow within the steep bifurcate shows potential instability and the potential for alternate channel bar formation. Bifurcation angle also defines the flow structures within the bifurcation with an increase in bifurcation angle increasing the flow velocity down both bifurcates. However, redistributive effects of secondary circulation caused by upstream curvature can very easily counter the effects of local bifurcation characteristics.
机译：河流分叉是辫状河流系统中的关键节点，它控制着水流和沉积物的分配，从而控制了河流辫状过程的动力学。最近的研究表明，某些几何构型会引起不稳定性，从而导致下游中间通道钢筋的形成和分叉的形成。但是，我们目前对分叉内的分流过程和下游分叉内的流动动力学知之甚少，这两者都是了解分叉稳定性所必需的。本文介绍了使用计算流体动力学（CFD）进行的数值敏感性实验的结果，目的是理解一系列理想化分叉的流动动力学。通过模拟流经曲率不同的曲折弯流的流场动力学，对一系列的通道斜率（0.005至0.03），分叉角（22°至42°）和一组受限的流入条件进行了几何灵敏度分析。分叉。结果表明，分叉的总坡度会影响通过分叉的流速，当引入坡度不对称性时，分叉处的流动结构会发生变化。在分叉演化方面，最重要的观察结果似乎是，一旦坡度不对称度大于0.2，陡峭的分叉内的流动就会显示出潜在的不稳定性和形成交替通道条的可能性。分叉角还定义了分叉内的流动结构，分叉角的增加增加了两个分叉处的流速。但是，由上游曲率引起的二次循环的再分配作用可以很容易地抵消局部分叉特征的影响。

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