Numerical investigation of the oscillatory free surface profiles of overfalls

This paper applies the two-phase least-squares finite element method (LSFEM) to investigate the free overfall. The flow patterns of various dropping flows were investigated for subcritical approach flow passing a vertical drop pool. It was discovered that, under certain conditions, the dropping flow forms a switching jet that oscillates up and down periodically and impinges on the bed and the downstream pool wall alternately. In this simulation, the flow is assumed steady and incompressible, the volume of fluid (VOF) method and continuous stress force (CSF) models with association of color function are incorporated for the determination of the interface between water and air. The formation of the model is carefully examined and the quantitative comparisons of the numerical simulations with previous numerical results and experimental measurements are shown to be in good agreement. For numerical simulations with different flow rates, the reattached length, water height after the fall, are investigated in both qualitative and quantitative ways.