Numerical Investigation on Energy Dissipation Processes Downstream of Labyrinth Weirs

Replacing existing classical weirs with labyrinth weirs is a proven approach to increase the discharge capacity when rehabilitating existing structures. The three-dimensional (3D) and complex flow field inside and immediately downstream of a labyrinth weir provides energy dissipation characteristics that should be considered for accurate, safe, and economic design. In this study, five labyrinth weirs with magnification ratios from 1 to 4 were placed in a rectangular channel with a horizontal slope. These geometries were investigated by using the FLOW-3D HYDRO software to study energy dissipation by those weirs. The observed results were further validated with available experimental laboratory data considering a set of discharges between 0.25 and 0.75 m3/s as an upstream boundary condition with free outlet downstream conditions. The Reynolds-Averaged Navier-Stokes (RANS) equations with a Re-Normalisation Group (RNG) k-ϵ turbulence scheme were employed in the solver. The results include the resolution of the downstream flow field, the quantification of the kinetic energy correction coefficient, and the momentum correction coefficient and residual energies across the labyrinth weirs in the streamwise direction. Both coefficients converge toward unity with increasing distance to the weir and discharge. Residual energy computational fluid dynamics (CFD) results are compared with prior labyrinth weir experimental data. Those results show an acceptable agreement of less than 10% discrepancy between the literature and the presented data. In addition, energy dissipation potentials of labyrinth and classical linear weirs are compared, quantifying the high amount of energy dissipation at labyrinths for similar flow rates.