Flow under vertical sluice gates: Flow stability at large gate opening and disambiguation of partial dam-break multiple solutions

The present paper deals with two open issues concerning the free orifice flow under vertical sluice gates, namely, the flow stability at large gate openings and the disambiguation of multiple solutions in the case of partial dam-break. The study of these problems, which are mutually connected, is based on ad hoc laboratory experiments and numerical simulations with a computational fluid dynamics model tracking the free surface with the two-phase volume of fluid method. A series of quasi-steady states is used to assess the threshold of relative gate openings that determines the passage from orifice flow to non-interacting flow; in addition, a set of dam-break experiments with partial gate opening (i.e., lower than the initial upstream water level) is performed to find reliable criteria to disambiguate multiple exact solutions supplied by the one-dimensional shallow water theory. It is found that the dependence of contraction and discharge coefficients on the relative gate opening has a dramatic impact on the stability of orifice flow at large gate openings.