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Velocity Distribution Along a Waterfall

Author(s): Yvan Bercovitz; Lebert Franck

Linked Author(s): Yvan BERCOVITZ

Keywords: Velocity; Jet; Waterfall; LDV; Energy dissipation

Abstract: Knowing the impact force of a waterfall helps us to understand the processes of scouring at the foot of the fall. Energy at the foot is usually estimated according to Bernoulli’s theorem. However, Castillo et al. (2014), followed by Bercovitz et al. (2016), observed energy dissipation within the jet. Ervine et al. (1997) and Castillo et al. (2006) considered the dissipation to be related to jet length exceeding break-up length, but Bercovitz et al. (2016) observed no jet break-up. Using a test waterfall, about 10 m high and caused by overflow on a thin crest weir about 1 m long, we confirme the observations reported by Bercovitz et al. (2016). The present study focuses on a flowrate of 200 l/s, with 2 types of measurement. Firstly, the jet was filmed over a fall of about 9 m, at an acquisition rate of 1,000 fps, confirming the absence of any jet break-up despite an unstable interface liable to disperse the jet. Secondly, and more importantly, we measured the vertical component of velocity, along the waterfall and within the thickness of the jet, using the Laser Doppler Velocimetry (LDV) technique. We confirmed a dissipative process within the jet, but to a lesser degree. Before presenting results for the vertical distribution of mean velocity, we focus on the method of measurement data-processing.

DOI: https://doi.org/10.3850/IAHR-39WC252171192022736

Year: 2022

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