Author(s): Subhojit Kadia; Nils Ruther; Elena Pummer
Linked Author(s): Elena Pummer, Nils Rüther
Keywords: Hydrodynamics channel bend nonuniform abrasion sediment movement supercritical flows
Abstract: A novel experimental investigation was performed in a mildly curved narrow channel under supercritical flow conditions to comprehend the hydrodynamics behind the nonuniform invert abrasion observed at sediment bypass tunnel bends, i. e., deeper abrasion toward the outer wall than near the inner wall, by inspecting the effects of channel curvature on the longitudinal velocity, secondary currents, turbulence characteristics, bed shear stress, and bed load movements. The physical model with a scale of 1:22 is a 0.2 m wide, 0.3 m deep, and about 16.8 m long channel with a plexiglass bend section representing the downstream bend part of the Solis sediment bypass tunnel from Switzerland. Results for the discharge of 0.07 m3/s, which generated a decelerating approach flow conditions with channel aspect ratio = 1.32 and Froude number = 1.9, are presented here. Turbulent flow characteristics were measured along the channel using a volumetric particle tracking velocimeter and the shake-the-box method. Furthermore, spherical sediment particle movements (sizing from 3.9 mm – 12.1 mm) were recorded using high-speed camera. The results show that the longitudinal velocity, turbulence parameters, and bed shear stress redistribute across the channel as the curvature-induced secondary currents develop in the flow direction, and that although experiencing a lower bed shear stress, the sediment particles always move toward the inner wall caused by the secondary currents. Therefore, such sediment shifting toward the inner wall causes the deeper abrasion observed at sediment bypass tunnel bends and downstream straight sections. These findings are crucial for future sediment bypass tunnel designs and for validating numerical models in the future.
Year: 2025