Impact pressures of turbulent high-velocity jets plunging in pools with flat bottom

Abstract

Dynamic pressures created by the impact of high-velocity turbulent jets plunging in a water pool with flat bottom were investigated. Pressure fluctuations were sampled at 1 kHz at the jet outlet and at the pool bottom using piezo-resistive pressure transducers, jet velocities of up to 30 m/s and pool depth to jet diameter ratios from 2.8 to 11.4. The high-velocity jets entrain air in the pool in conditions similar to prototype applications at water release structures of dams. The intermittent character of plunge pool flows was investigated for shallow and deep pools, based on high order moments and time correlations. Maximum intermittency was observed for pool depths at 5.6 jet diameters, which approximate the core development length. Wall pressure skewness was shown to allow identifying the zone of influence of downward and upward moving currents. List of symbols

Effect of pool confinement on pressures around a block impacted by plunging aerated jets

“…In the confinedbottom case, the deeper the pool, the more the pressure fluctuations were reduced. For the flat-bottom case, C' p values were higher for the deep pool (Y/d j = 11.1), in agreement with Bollaert and Schleiss (2005) and Manso et al (2007), who found that a developed jet impact on the bottom produces higher pressure fluctuations than a core jet.…”

“…To evaluate the dynamic pressures acting on a rock mass, a solid but fissured media has to be considered instead of loose sediments. Systematic experiments using high-velocity jets in a large facility were performed by Bollaert and Schleiss (2003b), Manso et al (2007), Federspiel (2011), and Duarte et al (2015 for pools with a flat bottom and by Manso (2006) and Manso et al (2009) for confined pool bottoms. These researches conducted in the Laboratory of Hydraulic Constructions (LCH) of the Ecole Polytechnique Fédérale de Lausanne (EPFL) developed a physically-based description of rock scour.…”

Measures to reduce dynamic plunge pool pressures generated by a free jet

“…Ervine et al (1997) mention that jet diffusion in the plunge pool is furthermore relevant for limited pressure fluctuations on the pool bottom, and that air entrained by the jet reduces bottom pressure amplitudes. Manso et al (2007) show that dynamic pressures at the bottom of shallow and deep pools often follow a Gaussian distribution.…”

Analysis of scour characteristics in presence of aerated crossing jets

“…Ervine and Falvey (1997) studied the behavior of water jets plunging through the atmosphere, analyzing the physical properties of the jets and their spreading. Furthermore, Manso et al (2007) conducted a comprehensive analysis on the dynamic pressures at the issuance and at the bottom of the pool investigating velocities and aeration conditions similar to those occurring in prototypes.…”