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Air entrainment onset in skimming flows on steep stepped spillways: an analysis

ABSTRACT We discuss, apply and validate several physics-based criteria for air entrainment into flows on steep stepped spillways, using laboratory observations and numerical results published elsewhere. To the best of our knowledge, this is the first time a validation of these criteria is undertaken for any chute flow in general, and for the skimming flow in steep stepped spillways in particular. To undertake the validation, we employed experimental and numerical data covering a considerable range of volume flow rates and step heights. We observed an overall good performance of most of the criteria, especially taking into account the intrinsic difficulties in defining the time-averaged location and depth of the inception point of air entrainment experimentally. Finally, we present two novel non-dimensional numbers designed to facilitate the physical interpretation of the location of the inception point of air entrainment.