Numerical study on flow pattern in meandering channels: The effect of hydraulic conditions and meander geometry

Natural rivers are one of the main sources of water and energy for humans. The design and management of exploitation of natural rivers systems will require a complete understanding of flow and sediment transport mechanics. Meanders are one of the most common types of rivers in nature, which have a very complex flow. The three-dimensional (3D) and complex characteristics of flow in meanderings bring up the necessity of investigating the flow pattern in this channel with 3D numerical models. This study aimed to investigate the flow pattern and predict the erosion and sedimentation site in the meandering. Also, the effect of the Froude number (Fr), the ratio of width-to-depth (B/h) and meander angle parameters on the flow field are investigated. In this study, the turbulent flow pattern in a sine-generated channel and the angle of 50∘ with a rectangular section with width = 40 cm and the rigid bed is studied using the 3D mathematical model SSIIM1.1. The primary and secondary flow patterns were studied using the turbulence models of k-ε and SST k-ω. Comparison of numerical models and experimental results showed that the flow pattern is predicted well by both turbulence models of turbulence. But in some cases, the SST k-ω model has provided closer results to the experimental results. The results show that the shear stress pattern depends on the changes in the Fr. But, the secondary flow pattern does not change much by changing the Fr. Also, changes in the B/h ratio affect the secondary flow pattern and shear stress pattern, so that for B/h<8, a small rotary cell is made in addition to the main rotary cell near the outer coast. The results also show that the flow pattern and shear stress depend on the channel angle.