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You are here : eLibrary : IAHR World Congress Proceedings : 36th Congress - The Hague (2015) ALL CONTENT : Water engineering : Integral turbulent length and time scales in hydraulic jumps: an experimental
Integral turbulent length and time scales in hydraulic jumps: an experimental
A hydraulic jump is a rapidly-varied open channel flow characterised by the sudden transition from a supercritical flow
motion to a subcritical regime. The transition is associated with a rapid increase of water depth, a highly turbulent flow
with macro-scale vortices, significant kinetic energy dissipation, a two-phase flow region and some strong turbulence
interactions with the free surface leading to splashes and droplet projection. The phenomenon is not a truly random
turbulent process because of the existence of low-frequency, pseudo-periodic coherent structures and fluctuating motion
in the jump roller. This study presents new measurements of turbulent air-water flow properties in hydraulic jumps,
including turbulence intensity, longitudinal and transverse integral length and time scales, for a range of Froude numbers
(3.8 < Fr1 < 8.5) at large Reynolds numbers (3กม104 < Re < 2กม105). The results showed a combination of both fast and
slow turbulent components. The respective contributions of the fast and slow motions were quantified using a novel triple
decomposition technique. The results highlighted the 'true' turbulent characteristics linked to the fast, microscopic
velocity turbulence of hydraulic jumps, while showing that slow-fluctuation turbulence intensity was a significant
contribution to the total. The high-frequency advection length scale and integral turbulent length scale exhibited some
maxima in the lower shear flow next to the invert. The turbulent length scales decreased along the roller as the fast
turbulence was dissipated. Comparison between the longitudinal advection and integral length scales indicated that the
advection and diffusion were not independent processes in the flow region immediately downstream of the jump toe. The
impact of slow fluctuations was large in the free-surface region and relatively smaller in the lower shear flow.
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Chapter : IAHR World Congress Proceedings
Category : 36th Congress - The Hague (2015) ALL CONTENT
Article : Water engineering
Date Published : 17/08/2015
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