Turbulent flow mechanisms in meandering channels with sediment transport

Abstract

This research aims to investigate the near-bed turbulent flow characteristics in a meandering channel with both mobile bed and immobile bed conditions. Experiments were performed in a prismatic rectangular meandering channel with a non-uniform sand bed of size d50 = 0.523mm. The three-dimensional instantaneous fluid velocity was collected using the Acoustic Doppler velocimeter which will provide important results related to the flow turbulence such as mean flow velocity, turbulence intensity, Reynolds shear stress, turbulent kinetic energy, skewness, kurtosis and turbulent anisotropy. The secondary current flow and the exchange of momentum in the form of turbulence kinetic energy, Reynolds shear stress and turbulent intensity at the inner layer of the flow are identified more in a mobile bed condition as compared to an immobile condition, which causes sediment transport. For the inner layer of the flow, turbulence intensity and turbulent kinetic energy are decreased in magnitude and gradually increase in the outer layer of flow for both the bed conditions. Higher turbulence anisotropy is noticed in the mobile bed condition than in the immobile bed condition, which shows more nonuniformities near the bed level for the mobile bed condition. This study may help in understanding the effect of sediment transport due to a turbulent flow structure in a sinuous alluvial channel. HIGHLIGHTS Comparison of turbulence between mobile and immobile bed conditions.; The near-bed longitudinal velocity profile increases with an increase in distance from the bed surface.; Negative values of Reynolds shear stress due to a narrow channel.; At the bend portion, the mobile bed has higher TKE than the immobile bed and vice versa at the cross-over section.; Turbulent anisotropy shows more nonuniformities of flow in the case of mobile beds.;

Keywords

• adv
• flow velocity
• immobile bed
• meandering channel
• mobile bed