Application of Three-Dimensional CFD VOF to Characterize Free-Surface Flow over Trapezoidal Labyrinth Weir and Spillway

The current literature for labyrinth weirs suggests that little attention has been paid to the complex free-surface flows generated downstream of these structures. In particular, there is no available guidance on the most appropriate model implementations to reproduce these flows numerically. This study presents new insights into the three-dimensional (3D) computational fluid dynamics (CFD) modeling of the free-surface flow over a labyrinth weir and spillway. The volume of fluid (VOF) model is implemented in both the OpenFOAM and ANSYS Fluent version 17.2 solvers to simulate four flow rates over a 1∶25 scale Froude number physical model. The results reveal the VOF method with the k-ε standard turbulence model and the piecewise linear interface construction algorithm is capable of well characterizing the complex flow behavior and features and provides appropriate predictions of velocities and depths. The model is also able to adequately estimate the labyrinth weir rating curve and the flow situation for various levels of tailwater in the spillway channel. The numerical predictions from the two solvers present greater consistency for the low flow rates. The increased discrepancies occurring for the largest flow rates are attributed to the different sensitivity to the mesh cell size as well as to the interface capturing schemes utilized.