Hydrodynamics of meandering river confluence under different junction angles and flow ratio: A numerical investigation

As an important node of the river network, the confluence plays a crucial role in river morphology, transporting sediment and the ecological processes. In the present work, the numerical simulation is conducted to explore the effects of the junction angle (α) and flow ratio (q*) on the hydrodynamic characteristics in a curved confluent channel by analyzing water surface elevation (WSE), longitudinal velocity (u), bed shear stress (τb̃), the Darcy–Weisbach friction coefficient (f), and the separation zone and secondary flow. The results reveal that the WSE increases with the increase in q* in the upstream of the confluence, while it decreases in the downstream. Both the u, τb̃, and f increase as the q* increases. Furthermore, the scale and aspect ratio (W*/L*) of the separation zone increase as the q* increases, and initially and then decrease as the α increases. However, the relative dimensions are independent of the q* and α. The secondary flow intensity (Sw¯) reaches its peak at the downstream of the confluence and increases with the increase in q*, and initially increases and then decreases as the α increases. It is worth noting that f increases as α increases, while the WSE, u, τb̃, scale of separation zone, and Sw¯ increase initially and then decrease, with the peak value occurring as α is 90°. By utilizing the velocity characteristics of the flow, a secondary flow coefficient (M) is introduced to describe the intensity and direction of the secondary flow. The findings of this study have further deepened the understanding of the hydrodynamic characteristics of curved confluent channels, providing valuable insights for river management and ecological restoration.