Topographic steering, flow recirculation, velocity redistribution, and bed topography in sharp meander bends
Topographic steering, flow recirculation, velocity redistribution, and bed topography in sharp meander bends
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DOI：
10.1029/2009wr008303
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发表时间：
2010-09
影响因子：
5.4
通讯作者：
K. Blanckaert
中科院分区：
文献类型：
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作者：
K. Blanckaert
床的地形和相关的流场进行了研究，在实验室配置的参数是代表尖锐的自然曲流弯曲。向内的质量输运区的特征在于准线性横向河床剖面，而向外的质量输运区，由明显的曲率变化引起，其特征在于弯曲内侧的准水平浅点沙坝，外侧的深水池，以及总横截面积的增加。这些准双线性河床剖面可归因于局限于池内的曲率诱导二次流。地形转向，主要是由于质量守恒，将大部分流量集中在弯曲的最深区域。但是，深度平均速度的模式（与河床地形的发展有关）在最深区域没有显示最大值。对深度平均流向动量方程的逐项分析表明，水面梯度是流速再分布的主要机制，尽管惯性和二次流也是占主导地位的过程。由于平面形状曲率的变化，逆压梯度和流动再循环的发生所需的条件建立。由于水流和河床地形之间的微妙反馈，一种不同类型的水流再循环发生在点坝上。泥沙输移模型中忽略垂向流速对床面的影响是弯曲河道形态动力学模型中的一个主要缺点。
The bed topography and associated flow field are investigated in a laboratory configuration with parameters that are representative for sharp natural meander bends. Zones of inward mass transport are characterized by a quasi‐linear transverse bed profile, whereas zones of outward mass transport, induced by pronounced curvature variations, are characterized by a quasi‐horizontal shallow point bar at the inside of the bend, a deep pool at the outside, and an increase in overall cross‐sectional area. These quasi‐bilinear bed profiles can be attributed to the curvature‐induced secondary flow that is confined to the pool. Topographic steering, mainly due to mass conservation, concentrates the major part of the discharge over the deepest zones of the bend. But the pattern of depth‐averaged velocities, which is relevant with respect to the development of the bed topography, does not show maximum values over the deepest zones. A term‐by‐term analysis of the depth‐averaged streamwise momentum equation reveals that the water surface gradient is the principal mechanism with respect to flow velocity redistribution, although inertia and secondary flow are also processes of dominant order of magnitude. A required condition for the occurrence of adverse pressure gradients and flow recirculation due to planform curvature variations is established. A different type of flow recirculation, due to a subtle feedback between the flow and the bed topography, occurs over the point bar. The neglect of the influence of vertical velocities impinging on the bed in models for sediment transport is identified as a major shortcoming in the modeling of the morphodynamics of meandering river channels.