Meander dynamics: A nonlinear model without curvature restrictions for flow in open?channel bends
Meander dynamics: A nonlinear model without curvature restrictions for flow in open?channel bends
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DOI：
10.1029/2009jf001301
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发表时间：
2010-12
影响因子：
--
通讯作者：
K. Blanckaert;H. Vriend
中科院分区：
文献类型：
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作者：
K. Blanckaert;H. Vriend
尽管计算能力快速发展，但通过简化且计算成本较低的模型来模拟曲流动力学仍然与大规模和长期过程的研究、概率预测或快速评估具有实际意义。现有的曲流模型总是基于温和曲率和缓慢曲率变化的假设，并且无法解释高曲率范围内的过程。本文提出了一种无曲率限制的曲流流体动力学非线性模型。它提供了主流的分布、次流的大小、床层剪切应力的方向以及曲率引起的额外能量损失。它包含现有的温和曲率模型，对于直线流仍然有效，并且与在比自然河流急弯更苛刻的条件下进行的实验室实验的实验数据令人满意地一致。所提出的模型揭示了驱动曲流弯中速度重新分布的机制及其对河流粗糙度 Cf、水流深度 H、曲率半径 R、宽度 B 和水深变化的依赖性。它将 Cf?1H/R 确定为一般曲折流体动力学的主要控制参数，并将相对曲率 R/B 确定为锐曲率效应。这两个参数在缓和弯曲的弯管中都很小，但在急剧弯曲的弯管中 O(1)，导致流动动力学存在显着差异。在轻微弯曲的弯道中，流向曲率变化可以忽略不计，但它们是急弯道中速度重新分布的主要机制。主流和次流之间的非线性反馈在急弯中也起着主导作用：它增加了能量损失并减少了次流、横向床坡度和速度重新分布。
Despite the rapid evolution of computational power, simulation of meander dynamics by means of reduced and computationally less expensive models remains practically relevant for investigation of large?scale and long?term processes, probabilistic predictions, or rapid assessments. Existing meander models are invariantly based on the assumptions of mild curvature and slow curvature variations and fail to explain processes in the high?curvature range. This article proposes a nonlinear model for meander hydrodynamics without curvature restrictions. It provides the distribution of the main flow, the magnitude of the secondary flow, the direction of the bed shear stress, and the curvature?induced additional energy losses. It encompasses existing mild curvature models, remains valid for straight flow, and agrees satisfactorily with experimental data from laboratory experiments under conditions that are more demanding than sharp natural river bends. The proposed model reveals the mechanisms that drive the velocity redistribution in meander bends and their dependence on the river's roughness Cf, the flow depth H, the radius of curvature R, the width B, and bathymetric variations. It identifies Cf?1H/R as the major control parameter for meander hydrodynamics in general and the relative curvature R/B for sharp curvature effects. Both parameters are small in mildly curved bends but O(1) in sharply curved bends, resulting in significant differences in the flow dynamics. Streamwise curvature variations are negligible in mildly curved bends, but they are the major mechanisms for velocity redistribution in sharp bends. Nonlinear feedback between the main and secondary flow also plays a dominant role in sharp bends: it increases energy losses and reduces the secondary flow, the transverse bed slope, and the velocity redistribution.