Turbulent processes at the entrance of a pool using flow visualization

Marquis, G. A.; Roy, Amitesh

doi:10.1201/9781439833865.ch9

Cited by 3 publications

(3 citation statements)

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“…These scaled horizontally with three to seven times the mean flow depth (Franca and Lemmin, 2008). Similar studies (Kirkbride and Ferguson, 1995;Dinehart, 1999;Buffin-Bélanger et al, 2000;Roy et al, 2004;Marquis and Roy, 2006;Lacey and Roy, 2008) were made in gravel-bed rivers with considerably larger relative submergence. The present research was carried out in a river with low relative submergence of 2.9, herein defined as h/D 50 (where h is the mean flow depth and D 50 the bed grain size diameter of which 50% of the grains have smaller diameters), and a wide range of bed roughness element sizes.…”

Section: Introductionsupporting

confidence: 58%

“…The occurrence of large-scale flow structures (LSFS) that are coherently organized throughout the flow depth and coexist with smaller scale turbulent dynamics has been reported in field and laboratory experiments of flows over gravel beds (Kirkbride and Ferguson, 1995;Buffin-Bélanger et al, 2000;Shvidchenko and Pender, 2001;Hofland and Booij, 2004;Roy et al, 2004;Marquis and Roy, 2006). In LSFS, the instantaneous velocity is synchronized over the whole region and it oscillates at a low frequency above or below the timeaveraged mean value (Jackson, 1976;Shen and Lemmin, 1999;Roy et al, 2004).…”

Section: Introductionmentioning

confidence: 97%

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Detection and reconstruction of large‐scale coherent flow structures in gravel‐bed rivers

Franca

Lemmin

2014

Earth Surf Processes Landf

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Large‐scale flow structures (LSFS) in the streamwise direction are important features of gravel‐bed river flows, because they may contribute to sediment transport and gas exchange. In the present study, these structures are detected using Huang's empirical mode decomposition and reconstructed with phase‐averaging techniques based on a Hilbert transform of the velocity signal. The analysis is based on the fluctuating component of 15 quasi‐instantaneous velocity profiles measured with a three‐dimensional (3D) acoustic Doppler velocity profiler (ADVP) in an armoured gravel‐bed river with a low relative submergence of 2.9 (ratio between flow depth and bed grain diameter). LSFS were identified in most of the measured profiles and consistently showed similar features. We were able to characterize the geometry of these large‐scale coherent structures: the front has a vertical linear shift in the time domain and a vertical profile corresponding to a first quarter moon with the apex situated at z/h ≈ 0.4. In the vertical, the front scales with flow depth h, and in the streamwise direction, LSFS scale with three to seven times the mean flow depth. On the bed, the effect of LSFS is a periodic non‐linear variation of the friction velocity on average between 0.90 and 1.10 times the mean value. A model for the friction velocity cycle resulting from LSFS oscillation is presented. Copyright © 2014 John Wiley & Sons, Ltd.

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Section: Introductionsupporting

confidence: 58%

Section: Introductionmentioning

confidence: 97%

Detection and reconstruction of large‐scale coherent flow structures in gravel‐bed rivers

Franca

Lemmin

2014

Earth Surf Processes Landf

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“…These studies have identified large‐scale flow structures formed by interaction with the bed [ MacVicar and Roy , , ; Lacey and Roy , ], which were detected through turbulent wake statistics [ Lacey and Roy , ]. These data confirm flow visualization analyses, showing a spatial scaling of the CFS with flow depth [ Marquis and Roy , ], while time series analysis has shown that these flow structures follow a power function that equates to a bursting cycle [ Paiement‐Paradis et al ., ].…”

Section: Previous Studies To Understand Coherent Flow Structures In Gmentioning

confidence: 63%

On the evolution and form of coherent flow structures over a gravel bed: Insights from whole flow field visualization and measurement

et al. 2016

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The microtopography of a gravel bed river has been shown to generate turbulent flow structures that originate from shear flow generated in the near-bed region. Although field and laboratory measurements have shown that such flows contain a range of coherent flow structures (CFS), the origin, evolution, and characteristics of the turbulent structures are poorly understood. Here we apply a combined experimental methodology using planar laser-induced fluorescence and particle imaging velocimetry (LIF-PIV) to measure simultaneously the geometric, kinematic, and dynamic characteristics of these CFS. The flow structures were analyzed by applying standard Reynolds decomposition and Lagrangian vortex detection methods to understand their evolution, propagation, and growth in the boundary layer and characterize their internal dynamical complexity. The LIF results identify large, individual, fluid packets that are initiated at the bed through shear that generate a bursting mechanism. When these large individual fluid packets are analyzed through direct flow measurement, they are found to contain several smaller scales of fluid motion within the one larger individual fluid parcel. Flow measurements demonstrate that near-bed shear controls the initiation and evolution of these CFS through merging with vortex chains that originate at the bed. The vortex chains show both the coalescence in the formation of the larger structures and also the shedding of vortices from the edges of these packets, which may influence the life span and mixing of CFS in open channels. The life span and geometric characteristics of such CFS are critical in influencing the duration and intensity of near-bed stresses that are responsible for the entrainment of sediment.

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Coherent flow structures in a depth‐limited flow over a gravel surface: The influence of surface roughness

et al. 2010

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1] Turbulent flows moving over a gravel bed develop large-scale, macroturbulent flow structures that are initiated at anchor clasts in the bed and grow and dissipate as they move upward through the flow depth. This paper extends previous research in which we investigated the influence of the Reynolds number on coherent flow structures generated over a gravel bed by assessing the importance of effective bed roughness. Here, we report on flume experiments in which flows over beds of decreasing surface roughness have been 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. These results indicate that as the effective roughness increases (1) the visual distinctiveness of the coherent flow structures becomes more defined throughout the flow depth, (2) the upstream angle of slope of the coherent flow structure increases, and (3) the reduction in streamwise flow velocity and turbulence intensity toward the upstream side of the structure becomes greater. Applying standard scaling laws, these structures appear shear-generated and form through a combination of both wake flapping and the reattachment of localized shear layers associated with flow separation around individual topographic protrusions. As the effective protrusion decreases, the scale of these coherent flow structures also decreases.

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Turbulent processes at the entrance of a pool using flow visualization

Cited by 3 publications

References 0 publications

Detection and reconstruction of large‐scale coherent flow structures in gravel‐bed rivers

Detection and reconstruction of large‐scale coherent flow structures in gravel‐bed rivers

On the evolution and form of coherent flow structures over a gravel bed: Insights from whole flow field visualization and measurement

Coherent flow structures in a depth‐limited flow over a gravel surface: The influence of surface roughness

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