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

ABSTRACT

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.

Keywords:

• Energy dissipation
• free-falling jet
• jet break-up length
• nappe flow
• plunge pool

Acknowledgements

This paper is dedicated to Professor Alan Ervine – excellent engineer, educator, and outstanding person. Those who were privileged to know him will always remember this outstanding hydraulician. Professors Puertas (Universidad La Coruña) and Dolz (Universidad Politécnica de Cataluña) provided data on the nappe flow case. The authors are also grateful to the Editor Professor Nikora, the Associate Editor and the two anonymous reviewers for their constructive comments that helped to improve the quality and clarity of the paper.

Funding

This work was supported by the Ministerio de Economía y Competitividad (Spain) and the FEDER (grant no. BIA2011-28756-C03-02).