Rectangular jet, or nappe flow, constitutes one of the energy dissipation methods used in the overtopping of dams. This paper reports new laboratory data on pressures, velocities and air entrainment and analyses the degree of break-up of a rectangular jet before entering the basin and the pressure fluctuations on the bottom of the pool. It is found that the maximum mean dynamic pressure coefficient of 0.86, which is valid for circular jets, is reduced to 0.83 for a rectangular jet. The study has also led to a relationship between the fluctuating pressure coefficient and the degree of the jet break-up. The peak pressure coefficient occurred for break-up length ratios (i.e. falling height/length) in the range of 1.00–1.20. The scaling effects are negligible for scales less than 1:10. The new set of characteristics given in the paper fills the current knowledge gap related to rectangular jets.

Paute-Cardenillo (owned by Celec Ep-Hidropaute) is a dam with maximum height 135 m located in the Paute River in Ecuador. Its hydroelectric production will be integrated at the National Electric System of Ecuador with an installed capacity of 600 MW which will produce 3300 GWh per year. To evaluate the stability and safety of the structure, it is necessary to ascertain the shape and dimensions of the scour generated downstream from the dam. We studied the scour, due to the operation of the free surface spillway (700 m³/s) and half-height outlets (1760 m³/s), with three complementary procedures: empirical formulae obtained in models and prototypes, semi-empirical methodology based on pressure fluctuations-erodibility index and computational fluid dynamics simulations. The free surface weir could generate a scour around 21 m, while the intermediate outlet could reach the intact rock, located 34 m below the initial river bed. A pre-excavated basin is proposed and the velocities and pressures are analyzed. The results demonstrated the suitability of combining different methodologies to achieve an adequate resolution of this complex phenomenon.

Rectangular jets constitute one of the energy dissipation methods in the overtopping of dams. The high turbulence and aeration phenomena that appear in falling jets and dissipation basins make it difficult to carry out studies based only on classical methodologies. There are studies modelling spillways with computational fluid dynamics which produces accurate results. However, the study of overflow nappe impingement jets has not been sufficiently examined. Simulations of free air–water overflow weirs are scarce, and require small mesh sizes and a high computational effort. This work seeks to address such simulation. Results obtained with ANSYS CFX are compared with laboratory measurements and empirical formulae. To identify the level of reliability of computed parameters, validation of air entrainment and velocity along free falling jets, thickness and break-up of jets, and pressures on the bottom of the plunge pool, are carried out by using a two-fluid model, turbulence models and mesh-size analysis. Good agreement is obtained with experimental and theoretical data. The results show that air entrainment in the jet is highly sensitive to the mesh size, while the choice of the turbulence model seems to have only a relative effect on the stagnation point.