The fluid dynamics of channel confluences are highly complex due to flow separation and secondary currents. Although numerous studies in the past few decades have focused on the numerical simulation of confluence flow, deformed beds were rarely used. This study attempts to address this issue through numerical simulation of the flow behavior in an open-channel confluence flume with an equilibrium degraded bed in OpenFOAM (version 6.0) to compare the results with a flatbed. In the present study, different turbulence models, including Reynolds-Averaged Navier–Stokes (RANS), large-eddy simulation (LES), and detached eddy simulation (DES) models were performed using rigid-lid and volume-of-fluid (VoF) methods. The accuracy of the models was statistically analyzed by comparing them with observation data. The results demonstrated that the LES model had the best performance, with a minimum average normalized root-mean-square error (NRMSE) of 3% under the VoF assumption. The investigation also further illuminated the intricate interplay of vortical structures within the confluence zone. Notably, the number and behavior of vortices were found to be influenced by channel geometry and size, as well as interactions between separated shear layers. Circulation within the separation zone near the inner bank differed in rotation between the degraded and flatbed cases.

The fluid dynamics of open channel confluences are highly complex due to the flow separation, mixing and secondary currents. Although numerous studies in the past few decades have focused on the numerical simulation of confluence flow, deformed beds were rarely used. This study attempts to address this issue through numerical simulation of the flow behavior in an open channel confluence flume with an equilibrium degraded bed in OpenFOAM. In the present study, six turbulence models, including Reynolds-Averaged Navier-Stokes (RANS) (standard k–ε, realizable k–ε, k–ω SST, V2-f), large-eddy simulation (LES) and detached eddy simulation (DES) models were performed using rigid lid and volume of fluid (VoF) methods. The accuracy of the models was statistically analyzed by comparing with the observation data, and their performance was prioritized accordingly. The results of this study demonstrated that the LES model had the best performance, with a minimum average normalized mean square error (NRMSE) of 9% under the VoF assumption and 27% under the rigid lid method.

1. Water quality standards have imposed restrictions on the release of pollutants generated by various industrial processes. Examples include discharge from desalination units, sewage, and waste he...