Author(s): S. Kadia; N. Rüther; E. Pummer

Linked Author(s):

Keywords: RSM; secondary currents; sediment bypass tunnel; supercritical flow; velocity dip

Abstract: One of the most effective techniques to combat reservoir sedimentation, especially for small to medium-sized reservoirs, is the installation of Sediment Bypass Tunnels (SBTs). SBTs are designed for supercritical narrow open channel flow conditions. In such narrow channels, the walls and the free surface boundaries can influence the flow characteristics and form secondary currents. These vortex structures can alter the longitudinal velocity distribution and form velocity dip. Besides, they can also alter the bed shear stress distribution and influence the sediment transport. Such complex phenomenon can be modelled using Reynolds Stress Models (RSMs). In this study, the full Launder Reece and Rodi (LRR) pressure-strain model was implemented in OpenFOAM® and the simulated results were compared with former experimental results for flow depth = 0.16 m, Reynolds number = 5.7×105, Froude number = 1.84, and channel aspect ratio = 1.25. In addition, the dissipation rate of turbulent kinetic energy at the free surface was modelled following literature. The simpleFoam solver, which is based on the SIMPLE algorithm, was used for the steady state simulation. The predicted velocity distributions, secondary currents, velocity dip, turbulence intensity distributions, and lateral variation in bed shear stress are consistent with literature. The results show that the simulated maximum longitudinal velocity and the cross-sectional average bed shear stress are 0.34% and 0.74% lower than the observed values. An intermediate vortex was developing between the free surface vortex and the bottom vortex for the tested case. However, it remained as a part of the free surface vortex.

DOI: https://doi.org/10.26077/5e0b-783d

Year: 2022