Prediction of Air Entrainment in Skimming Flow over Stepped Spillways using Numerical Methods

This study presents a numerical investigation into skimming flow over a large scale experimental stepped spillway. High levels of aeration generally occur during skimming flow over stepped spillways, however, this aeration has not previously been predicted well using multiphase numerical modelling techniques. The Volume of Fluid (VOF) and Eulerian multiphase models, in conjunction with the Realisable k-ε and SST k-ω­ turbulence models, are evaluated. In this study certain aspects of the flow are well predicted by both the VOF and Eulerian models, however, only the Eulerian approach is able to model air being entrained into the flow. In the study the Eulerian model, in conjunction with the SST k-ω model, makes accurate prediction of the velocities and flow depths throughout the spillway as well as the air concentrations in the aerated region. The Eulerian model with the SST k-ω model has been shown to provide a simple, potentially accurate method for predicting the location of the inception point of air entrainment by inspection of the air concentration contours.