Processes governing the flow redistribution in sharp river bends
Processes governing the flow redistribution in sharp river bends
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DOI：
10.1016/j.geomorph.2011.04.049
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发表时间：
2012-08
期刊：
影响因子：
3.9
通讯作者：
W. Ottevanger;K. Blanckaert;W. Uijttewaal
中科院分区：
文献类型：
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作者：
W. Ottevanger;K. Blanckaert;W. Uijttewaal
基于Blanckaert和de Vriend（2003，2010）的无曲率限制的降阶非线性模型对最近三个实验的模拟结果，对控制急弯河道流速重分布的水动力过程进行了深入研究。该模型成功地模拟了三个实验中的流量再分配和二次流。结果表明，流量再分布主要取决于地形转向，曲率变化和二次流，在广泛的不同配置，包括轻度到急剧弯曲的弯曲，窄浅弯曲，光滑粗糙弯曲，弯曲与额外的复杂性，如水平回流区或河床植被斑块。这三个主要过程的相对重要性取决于具体情况，并受参数Cf− 1 H/B、R/B和流向曲率变化的控制。第一个参数表征河段，而第二个和第三个参数是各个弯道的特征。缓弯和急弯的水动力过程有很大的不同。首先，曲率变化引起的速度重分布在轻度弯曲的弯道中可以忽略不计，但在急弯中占主导地位。这个结果是相关的，因为大多数曲流模型是基于弱曲率变化的假设。第二，非线性水动力相互作用在急弯中起主导作用，在急弯中，轻度曲率模型过度预测二次流，在某些情况下甚至错误地将其识别为控制速度再分布的主导过程，这导致不满意的流量预测。由非线性水动力相互作用引起的二次流强度的减小伴随着横向床面坡度的减小，这减小了地形转向的影响
Insight is provided in hydrodynamic processes governing the velocity redistribution in sharp river bends based on simulations of three recent experiments by means of Blanckaert and de Vriend's (2003, 2010) reduced-order nonlinear model without curvature restrictions. This model successfully simulated the flow redistribution and the secondary flow in all three experiments. The results indicate that the flow redistribution is primarily governed by topographic steering, curvature variations and secondary flow, in a broad range of different configurations, including mildly to sharply curved bends, narrow to shallow bends, smooth to rough bends, bends with additional complexities such as horizontal recirculation zones or patches of riverbed vegetation. The relative importance of these three dominant processes is case dependent, and controlled by the parameters Cf− 1H/B, R/B and streamwise curvature variations. The first parameter characterizes a river reach, whereas the second and third parameters are characteristics of individual bends. Major differences exist between the hydrodynamic processes in mildly and sharply curved bends. First, velocity redistribution induced by curvature variations is negligible in mildly curved bends, but the dominant process in sharp bends. This result is relevant, because most meander models are based on the assumption of weak-curvature variations. Second, nonlinear hydrodynamic interactions play a dominant role in sharp bends, where mild-curvature models overpredict the secondary flow and in some cases even falsely identify it as the dominant process governing the velocity redistribution, which leads to unsatisfactory flow predictions. The reduction in secondary flow strength provoked by the nonlinear hydrodynamic interactions is accompanied by a reduction in the transverse bed slope, which reduces the effect of topographic steering