Hydrodynamic Structure and Turbulent Characteristics of Low-Slope Bedrock Bend Reach with Constant Curvature

Abstract

Recent studies have indicated that low-slope bedrock reaches are more common in nature (the bedrock surface slope is slightly lower than 0.005). This paper focuses on the hydrodynamic structure and turbulent characteristics of low-slope and critically sharp bedrock bends under flood conditions. Three experiments under different flood frequencies were conducted to investigate the influence of the ratio of centerline curvature radius to depth (Rc/H) on the distribution and characteristics of the secondary flow, turbulence, and momentum transport measured by acoustic Doppler velocimeter (ADV). The results were then compared with the flow structure of a sharp bend. Our results indicated that the distribution area and the intensity of the secondary flow decreased with Rc/H, especially in the outer-bank cell and the center-region cell. The lower Rc/H was, the more obvious the flow separation at the inner bank was. The core area of the turbulent kinetic energy moved upstream gradually, and its intensity increased with Rc/H. The friction factor increased in the upstream bend and did not move further upstream when Rc/H was below 13.6. The intensity of the transverse bed shear stress decreased with Rc/H in a critically sharp bend, and the maximum value near the upstream centerline implied the potential erosion in the bedrock bend. These experimental results are conducive to understanding the flow process of erosion and deposition in the bedrock bend reach.