Determination of Scale Effects for a Scaled Physical Model of a Labyrinth Weir Using CFD

In the present study the three dimensional (3D) Computational Fluid Dynamics (CFD) Volume of Fluid (VOF) model is employed to reproduce the complex hydraulic flows over a labyrinth weir and a spillway for two flow rates, 40 m3/s and the PMF event of the scheme, 159.5 m3/s. The VOF model is implemented in two solvers: the open source platform OpenFOAM and the commercial CFD package ANSYS Fluent. Validation is undertaken by modelling the scaled physical model of the scheme. Prototype scale simulations of the two flow rates are undertaken, with comparisons between predictions at the two scales being used to establish discrepancies between the two scales. Overall the two solvers predict the prototype flows to be shallower and with higher velocities than those at model scale, but with these scale effects becoming less prominent for increasing flow rates. In the 40 m3/s case the wave structures in the prototype present elongation compared to those at model scale. In the PMF case, in addition to elongation, the wave structures also change in position. Work is currently underway with the modelling of further flow rates in order to investigate the discrepancies between scale and prototype simulations with increased detail and determine limits to minimise impact of scaling.