It remains an open question whether the state of knowledge on bend hydrodynamics applies to sharp bends in the largest river systems on Earth. This paper reports a field investigation into the hydrodynamics in two consecutive sharp bends of the Middle Yangtze River (MYR), and demonstrates that the reduced-order model of Blanckaert and de Vriend is able to resolve the secondary flow strength and continuous flow redistribution in rivers of this size to high accuracy. Consequently, the model has been validated over the entire range of scales. These two bends show similarities to those of smaller size in terms of bathymetry, flow redistribution, and secondary flow evolution. The transverse location of the core of maximum velocity along the bends lags behind the thalweg by approximately half a width. A center-region cell of secondary flow develops over the outer bank near the apex, and gradually decays downstream until it completely vanishes at the bend exit. Both bends are mildly curved from the perspective of hydrodynamic modeling, with a weak interaction between the secondary flow and primary flow, although they are sharply curved from the perspective of geomorphology (width/radius > 0.5). A term-by-term analysis of the model indicates that the flow redistribution is primarily controlled by planimetric changes in curvature and by topographic steering, and is slightly influenced by the secondary flow. However, the secondary flow may indirectly affect the flow redistribution by conditioning the bed topography. Important knowledge gaps remain with respect to the coupling between the hydrodynamic and morphological processes.

中文翻译：

---

长江中游两个急弯的二次流与流量再分配

关于弯曲流体动力学的知识状态是否适用于地球上最大河流系统中的急转弯仍然是一个悬而未决的问题。本文报道了对长江中游 (MYR) 两个连续急转弯处的流体动力学的实地调查，并证明了 Blanckaert 和 de Vriend 的降阶模型能够解决河流中的二次流强度和连续流重新分布问题。这种尺寸的高精度。因此，该模型已在整个尺度范围内得到验证。这两个弯道在水深测量、流量重新分布和二次流演变方面与较小尺寸的弯道相似。沿弯道的最大速度核心的横向位置落后于 thalweg 大约一半的宽度。二次流的中心区域单元在顶点附近的外岸上发展，并逐渐向下游衰减，直到它在弯道出口处完全消失。从流体动力学建模的角度来看，这两个弯道都是轻微弯曲的，二次流和一次流之间的相互作用很弱，尽管从地貌学的角度来看它们是急剧弯曲的（宽度/半径 > 0.5）。模型的逐项分析表明，流重新分布主要受曲率的平面变化和地形转向控制，并受二次流的轻微影响。然而，二次流可能会通过调节床的地形间接影响流量的重新分布。在流体动力学和形态过程之间的耦合方面仍然存在重要的知识差距。