Plunge pool dynamic pressures: a temporal analysis in the nappe flow case

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.