Curved confluent channels are widespread in the Yangtze River basin, and seasonal variation of the main channel width (W1) affects hydrodynamics, sediment deposition, and pollutant dispersal at the confluence zone. To explore the effect of main channel width and flow ratio (q*) on the hydraulic characteristics in the curved confluent channel, the Renormalization Group k–ε turbulence model is employed to conduct a detailed analysis of water surface elevation (WSE), longitudinal velocity distribution, separation zone, and secondary flow. The results indicate that the confluent tributary lowers WSE of the main channel compared to the case without tributary; additionally, the WSE decreases with increasing W1 and increases with increasing q*. As W1 increases, the longitudinal velocity on the inner bank increases, while that on the outer bank decreases in the downstream region of the confluence zone. The scale of the separation zone increases with increase in W1 or q*. The variation of outer bank circulation in the downstream channel of the confluence zone is the most obvious, which decreases with increase in W1 and increases with increase in q*. A formula for solving the secondary flow intensity applicable to confluence channel has been proposed, and the mean secondary flow intensity increases with increase in W1 or q*. The findings of this study not only enhance our understanding of the hydrodynamic characteristics of curved confluence channels but also offer a theoretical foundation for riverbank stabilization and channel management.

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.

Confluent channels are ubiquitous in nature, with tributary morphology exhibiting diverse forms. To explore the influence mechanism of tributary morphology in a confluent channel on the hydrodynamic characteristics of the main channel, the validated renormalization group k–ε turbulence model is employed in this work to investigate the effect of tributary morphology of the upstream bend (UB), straight channel (SC), and downstream bend (DB) with varying flow ratio (q*) on the hydrodynamic characteristics of a 90° equal-width confluent channel. Results reveal that the tributary morphology has a significant impact on the flow structure, separation zone, and secondary flow of the main channel. Mean vortex structures form within the tributary before it flows into the main channel when the tributary morphology is UB, resulting in a larger area of horizontal vortices near the water surface in the downstream of the confluence zone. Compared with SC and DB, the dimensionless length of the separation zone and secondary flow intensity are the largest when the tributary morphology is UB. In addition, the variation range of dimensionless length and width as well as secondary flow intensity with various tributary morphologies decreases with increasing q*. The findings of this study will contribute to a better understanding of the hydrodynamic characteristics of the 90° equal-width confluence, providing valuable insights for river management and ecological restoration.

Curved confluent channels are widely distributed in natural river networks, where tributaries enter the main channel at different confluence locations. To investigate the effects of the tributary confluence location on the flow structure in the confluence, a numerical model based on the validated renormalization group k–ε turbulence model is established. The effects of tributary confluence locations (θ) and flow ratios (q*) on the water surface elevation (WSE), longitudinal velocity distribution (u), separation zone, and secondary flow were systematically examined. The results show that the WSE increases with increasing q* in the upstream of the confluence, while it decreases in the downstream. Regarding the velocity distribution, θ alters the direction of the transverse velocity (v) in the confluence and the position of the maximum velocity zone. In contrast, increasing q* enhances the longitudinal velocity (u) and enlarges the maximum velocity zone. In addition, the scale of the separation zone increases with increasing q*. As θ increases, the separation zone scale initially increases and then decreases, reaching relatively large values near θ = 90°–120°. The secondary flow primarily consists of the inner bank circulation and the outer bank circulation. The mean secondary flow intensity (Sw¯) reaches its peak value downstream of the confluence, and the peak value increases with increasing q*. The dimensionless flow recovery distance (Xr*) exhibits a unimodal variation with q* and θ. These findings advance the understanding of momentum redistribution, the three-dimensional structure of the separation zone, and secondary flow evolution in curved confluent channels.

The radius-to-width ratio has an obvious impact on the flow structure within curved channels, which most natural rivers possess, but there are currently few studies on the influence of the radius-to-width ratio of a tributary (R/B) on the hydrodynamic characteristics of a confluent channel. In order to contribute to this field of research, this study employed the RNG k-ε turbulence model, which has good applicability and accuracy for confluence, to investigate the effects of the R/B and flow ratios (q*) on the hydraulic characteristics of confluence. The results reveal that the numerical model can effectively simulate the velocity distribution in the confluence. The values of the key errors are all relatively small (e.g., the value of Mean RMSE is 0.05), and the flow patterns near the bed and water surfaces are different. The maximum velocity zone (MVZ) and the scale of the separation zone (SZ) increase as R/B increases; conversely, the MVZ and the scale of the SZ decrease as the q* increases. Upstream of the confluence, turbulent kinetic energy (TKE) increases and decreases as R/B and q* increase, respectively, while TKE downstream of the confluence hardly changes. Furthermore, the size of the SF decreases as R/B increases. The value of $\overline{S_w}$ peaks downstream of the confluence, increases with the increase in the R/B, and decreases with the increase in the q*. The results of this study will contribute to a better understanding of the hydrodynamic characteristics of confluence and provide valuable insights for the management and ecological restoration of confluent channels.