  Numerical modelling of flow in stepped spillways is considered, focusing on a
highly economical approach combining interface capturing with explicit
modelling of air entrainment. Simulations are performed on spillways at four
different Froude numbers, with flow parameters selected to match available
experimental data. First, experiments using the model developed by Lopes et al.
(Int. J. Nonlin. Sci. Num., 2017) are conducted. An extensive simulation
campaign is used to carefully evaluate the predictive accuracy of the model,
the influence of various model parameters, and sensitivity to grid resolution.
Results reveal that, at least for the case of stepped spillways, the number of
parameters governing the model can be reduced. A crucial identified deficiency
of the model is its sensitivity to grid resolution. To improve the performance
of the model in this respect, modifications are proposed for the interface
detection algorithm and the transport equation for the volume fraction of
entrained air. Simulations using the improved model formulation demonstrate
better agreement with reference data for all considered flow conditions. A
parameter-free criterion for predicting the inception point of air entrainment
is also tested. Unfortunately, the accuracy of the considered conventional
turbulence models proved to be insufficient for the criterion to work reliably.
