Application of an acoustic particle flux profiler in particleladen open-channel flow

Shen, Chao; Lemmin, Ulrich

doi:10.1080/00221686.1999.9628256

Cited by 36 publications

(48 citation statements)

References 15 publications

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“…The results obtained in this analysis agree with previous work in which the development of the flow structure has been found to be proportional to the flow velocity (i.e., Reynolds number if flow depth is kept constant [ Shvidchenko and Pender , 2001]), and identifies structures similar to the classical bursting phenomenon in which low‐momentum fluid is ejected from the bed [ Grass , 1971; Talmon et al , 1986; Shen and Lemmin , 1999]. However, the present study shows that these flow structures develop over the large anchor clasts in the bed, potentially by wake flapping.…”

Section: Discussionsupporting

confidence: 89%

“…The downstream scale of these structures has been proposed to be between 4 h and 7 h , with this scale increasing as bed roughness decreases [ Klaven , 1966; Klaven and Kopaliani , 1973; Shvidchenko and Pender , 2001]. It has also been suggested that the origin of these flow structures is closely linked to the bursting phenomena in turbulent boundary layers [ Grishanin , 1990; Yalin , 1992; Smith , 1996; Grass and Mansour‐Tehrani , 1996] where (1) ejected, low‐momentum fluid travels across the entire flow depth irrespective of the bed roughness [ Grass , 1971; Talmon et al , 1986 ; Shen and Lemmin , 1999] and (2) high‐momentum fluid moves from near the water surface toward the bed [ Rashidi and Banerjee , 1988; Grass et al , 1991]. However, in most physical modeling studies, the rough boundaries have been restricted to well‐sorted beds composed of homogenous particles where skimming flow develops [ Grass , 1971; Grass et al , 1991; Krogstad et al , 1992].…”

Section: Introductionmentioning

confidence: 99%

“…Indeed, process information derived from data collected from previous studies provides contradictory evidence. Some studies have been interpreted as showing low‐frequency velocity fluctuations corresponding to a spatial scale of the order of the flow depth [ Komori et al , 1982; Grinvald and Nikora , 1988; Clifford et al , 1992; Lapointe , 1992; Nezu and Nakagawa , 1993; Robert et al , 1993; Roy et al , 1996; Cellino and Graf , 1999; Shen and Lemmin , 1999]. However, other authors do not detect any regular periodicity in the turbulent fluctuations of flow [ Grinvald , 1974; Nikora and Smart , 1997], which suggests the coherent flow structures are randomly distributed in time and space [ Nychas et al , 1973; Smith , 1996; Nikora and Goring , 1999].…”

Section: Introductionmentioning

confidence: 99%

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Coherent flow structures in a depth‐limited flow over a gravel surface: The role of near‐bed turbulence and influence of Reynolds number

Hardy¹,

Best²,

Lane³

et al. 2009

J. Geophys. Res.

111

134

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[1] In gravel bed rivers, the microtopography of the bed exerts a significant effect on the generation of turbulent flow structures. Although field and laboratory measurements have indicated that flows over gravel beds contain coherent macroturbulent flow structures, the origin of these phenomena, and their relationship to the ensemble of individual roughness elements forming the bed, is not quantitatively well understood. Here we report upon a flume experiment in which flow over a gravel surface is quantified through the application of digital particle imaging velocimetry, which allows study of the downstream and vertical components of velocity over the entire flow field. The results indicate that as the Reynolds number increases (1) the visual distinctiveness of the coherent flow structures becomes more defined, (2) the upstream slope of the structures increases, and (3) the turbulence intensity of the structures increases. Analysis of the mean velocity components, the turbulence intensity, and the flow structure using quadrant analysis demonstrates that these large-scale turbulent structures originate from flow interactions with the bed topography. Detection of the dominant temporal length scales through wavelet analysis enables calculation of mean separation zone lengths associated with the gravel roughness through standard scaling laws. The calculated separation zone lengths demonstrate that wake flapping is a dominant mechanism in the production of large-scale coherent flow structures in gravel bed rivers. Thus, we show that coherent flow structures over gravels owe their origin to bed-generated turbulence and that large-scale outer layer structures are the result of flow-topography interactions in the near-bed region associated with wake flapping.

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Section: Discussionsupporting

confidence: 89%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Coherent flow structures in a depth‐limited flow over a gravel surface: The role of near‐bed turbulence and influence of Reynolds number

Hardy¹,

Best²,

Lane³

et al. 2009

J. Geophys. Res.

111

134

View full text Add to dashboard Cite

show abstract

“…In their experiments, they showed that the motion of these particles responded to rather extreme flow ejection events. An acoustic particle flux profiler had been used in a particle‐laden open‐channel flow in Shen and Lemmin []. Correlations between the large‐scale structures of the velocity fluctuation field and the concentration fluctuation field were obtained.…”

Section: Introductionmentioning

confidence: 99%

Quantification of the bed load effects on turbulent open‐channel flows

Liu

et al. 2016

JGR Earth Surface

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With a computational model combining large eddy simulation and a discrete element model, detailed quantification of the bed load effects on turbulent open‐channel flows is presented. The objective is the revelation of bed load particle impact on the mean flow properties and coherent structures. Two comparative numerical experiments with mobile and immobile beds are conducted. Mean properties (e.g., velocity and Reynolds stress profiles) show good agreement with experimental data. Comparing the mobile and immobile cases, the effective bed position is nearly the same, whereas the equivalent sand roughness is changed. The flow experiences higher bottom shear stress over immobile bed. To quantify impact on turbulent structures, a revised quadrant analysis is performed to calculate four key parameters of ejection and sweep events (duration, maximum shear stress, transported momentum, and period). Results show that the ejection and sweep events have comparable importance in the outer region. However, sweep becomes dominant in the near‐wall region. The motion of particles enhances the sweep dominance by breaking up the ejection structures and decreasing their occurrence ratio. The results also suggest that the ejection events are easier to be influenced by the particle motions because they originate from the near‐wall region. The duration, maximum shear stress, and transported momentum decrease close to the bed. The period remains relatively constant in the outer region but decreases near the bed. Visualization of the coherent structure reveals that the instantaneous particle motion has strong correlation with the bursting cycle events.

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“…ADIs can also be used to measure particle flux dynamics (Shen and Lemmin 1999;Cellino and Lemmin 2001;Hurther and Lemmin 2003). Profiles are obtained by gating the backscattered signal according to the time of flight.…”

mentioning

confidence: 99%

Improving the accuracy of four‐receiver acoustic Doppler velocimeter (ADV) measurements in turbulent boundary layer flows

Doroudian

Bagherimiyab

Lemmin

2010

Limnology & Ocean Methods

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Acoustic Doppler instrument measurements suffer from random spikes and Doppler noise. Using a fourreceiver ADV (acoustic Doppler velocimeter; Vectrino manufactured by Nortek) that allows recording beam velocities, we combine a spike-removal procedure on the beam velocities with a noise-reduction method on the flow velocities to improve turbulence measurements. We compare the results with those obtained from ADVP (acoustic Doppler velocity profiler) measurements under the same conditions, i.e., in turbulent open-channel flow over a coarse-grained bed. It is shown that spikes are best removed from ADV beam velocity data before calculating flow velocities, thereby correcting all three flow velocity components at the source. Spikes in beam velocities do not correlate with low correlation values. ADVP data generally have few spikes and do not need spike removal treatment, showing that spikes are instrument related. The noise reduction method is based on the decorrelation of the Doppler noise terms contained in two vertical velocities redundantly sampled in the same volume. The combined ADV data treatment is sufficient to significantly extend the resolved frequency range in the velocity spectra. It reduces RMS values by up to a factor of 2, and the corrected values agree with ADVP results and theoretical predictions, indicating that both treatments are needed. Owing to spatial averaging effects over the ADV sample volume, a sampling frequency limit of close to 50 Hz is determined by the deviation of the spectra from the -5/3 slope.

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Application of an acoustic particle flux profiler in particleladen open-channel flow

Cited by 36 publications

References 15 publications

Coherent flow structures in a depth‐limited flow over a gravel surface: The role of near‐bed turbulence and influence of Reynolds number

Coherent flow structures in a depth‐limited flow over a gravel surface: The role of near‐bed turbulence and influence of Reynolds number

Quantification of the bed load effects on turbulent open‐channel flows

Improving the accuracy of four‐receiver acoustic Doppler velocimeter (ADV) measurements in turbulent boundary layer flows

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