Investigation on the width-to-depth ratio effect on turbulent flows in a sharp meandering channel with periodic boundaries using large eddy simulations

As one of the most common river patterns in nature, meandering river has very complex flow structures in its curved channel bends, including secondary flow structure and primary flow velocity redistributions. To date, most of the studies have been carried out on the flow structures in channel bends with unavoidable influences from inlet and outlet boundaries, while a streamwise periodic boundary can overcome this shortcoming elegantly. In this paper, large eddy simulations (LES) are employed to investigate the complex flow structures in periodically continuous sharp sine-generated bends. The influence of width-to-depth ratios and dimensionless curvature radiuses are studied. The results highlight two additional vortex structures beyond the commonly known secondary currents: The recirculation zone (RZ) and the inner bank cell (IBC). The width-to-depth ratio shows the determining effect on the recirculation zone. The size of recirculation zone is usually bigger in sine-generated-curve (SGC) channel with large width-to-depth ratios. The biggest recirculation zones appear between the zero-curvature section and the apex section. The inner bank cell only forms in SGC channels with small width-to-depth ratios and low curvature. For SGC channel with large width-to-depth ratios, only one circulation cell is observed near the inner bank. The spatial variations of turbulent features are also revealed by statistical analysis based on the LES sampling data. Results highlight remarkable effect of width-to-depth ratio and dimensionless curvature radius on the turbulent kinetic energy (TKE) and bed shear stress in SGC channels.