Author(s): Guanghui Yan; Saiyu Yuan

Linked Author(s): Saiyu Yuan

Keywords: River confluence; Compound channel; Hydrodynamic characteristics; Coherent structures

Abstract: The confluence of rivers is a critical node for controlling the water and sediment transport as well as the river ecology changes. At the confluence of the Yangtze River and Poyang Lake, the floodplain on one side of Poyang Lake occupies about half of the river width, forming a typical compound channel. The flow of the tributary floodplain must have a significant impact on the confluence process, but there is no research on the hydrodynamic characteristics. Through detailed laboratory experiments and numerical simulations, the threedimensional velocity field, turbulence kinetic energy, and Reynolds shear stress distribution, shear layer, separation zone, and secondary flow under the effects of the floodplain were analyzed. The experimental results show that under the influence of the floodplain, larger scale and stronger secondary flow motion, and tilted shear layers were observed, which were related to flow separation at the floodplain step and high-momentum water flow in the tributaries. In addition, the numerical method based on the Reynolds stress turbulence model (RSM) was used to study the influence of eight different characteristics on the flow structure. It was found that the tributary floodplain significantly increased the strength and size of the secondary flow, and the position of the secondary flow depended on the height and width of the floodplain. The width of the separation zone increased with the increase in the width and height of the tributary floodplain, which was due to the limitation of the floodplain on the overbank flow area and the enhancement of the momentum of the tributary flow. However, when the width of the floodplain exceeded half of the width of the tributary, the width of the separation zone increased but the length decreased, and the large-scale secondary flow would destroy the downstream separation zone and cause a local rise in the water surface. The research results enrich the understanding of the water flow structure under the compound confluence and also contribute to the understanding of the hydrodynamic processes at the confluence of the Yangtze River and Poyang Lake.

DOI: https://doi.org/10.3850/978-90-833476-1-5_iahr40wc-p0107-cd

Year: 2023