Numerical investigation on the hydraulic characteristics of curved open channel confluence with different main channel widths

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.