Prediction of the transition nappe/skimming flow on a stepped channel

Abstract

On a stepped channel, two distinct flow regimes may occur : nappe flow for low discharges and flat slopes, andskimming flow for larger flow rates. A simple analytical method to predict the onset of skimming flow is presented.The method is based upon the change of momentum direction at the impact of the jet on the downstreamstep. The results of the analysis are compared with existing experimental data. The onset of skimmingflow is expressed in terms of the initial Froude number and jet angle. The generalisation of the study resultsenables to predict the onset of skimming flow and hence the risk of jet deflection at the first upstream step.