Steady state model and experiment for an oscillating grid turbulent two-layer stratified flow

Verso, Lilly; Reeuwijk, Maarten van; Liberzon, Alex

doi:10.1103/physrevfluids.2.104605

Cited by 10 publications

(19 citation statements)

References 30 publications

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“…µ e α ≈ 1 in (10) which substituted in (11), leads for this onset u d = w s ⇐⇒ u δ = νw s d ≈ 2 mm/s (18) and θ ch ≈ 1 18 (19) In figure 9-a, horizontal motion initiation happens with u δ ≥ 2 mm/s. To know which force balances buoyancy in the initiation of vertical motion, parameter A needs to be estimated.…”

Section: Please Cite This Article As Doi:101063/15141943mentioning

confidence: 96%

“…In figure 10, the particle is ejected with an overall velocity of the order of 3 37 , to be lifted up by the flow, the particle needs to be exposed during a specific duration T to a flow favoring both a horizontal movement and a lift up ("impulse approach"). In other words to have a particle set up in the vertical erosion process, both the horizontal movement and lift up criteria (see (18) and (20)) need to be verified by the flow close by the particle for a duration of at least T .…”

Section: Please Cite This Article As Doi:101063/15141943mentioning

confidence: 99%

“…The number of favorable velocity events at f = 4 Hz (n f e_4Hz ) and f = 6 Hz (n f e_6Hz ) have also been counted. In each case the number of favorable events have been determined as previously: by counting the number of events that fulfilled criteria (18) and (20) with T within [0.3-0.5s] (impulse approach) or the modified criteria (24) with T = 0s (instantaneous approach). The concentrations C 6Hz and C 4Hz associated with the numbers of favorable events determined with the "impulse approach": n f e_4Hz and n f e_6Hz respectively, have been determined from equation (23).…”

Section: Please Cite This Article As Doi:101063/15141943mentioning

confidence: 99%

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Sediment erosion in zero-mean-shear turbulence

2020

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Turbulence plays an evident role in particle erosion that in many practical situations superimposes with the action of a mean flow. In this paper, the turbulence effect on particle erosion is studied under zero-mean flow conditions, by using the turbulence generated by an oscillating grid. The stirring grid is located more than two mesh size away from the particle layer. The zero-mean flow below the grid has been qualified by revisiting Matsunaga et al. 1 k − ε model. The turbulence efficiency on the settling/resuspension of the particles is quantified for various turbulence intensities, varying the size, the nature of the particles, and their buoyancy relative to the fluid. We find that the concentrations C of eroded particles collapse fairly well onto a single trend for C ≤ 5 × 10 −2 , when plotted as a function of the ratio between the flux of turbulent kinetic energy (TKE) at the particle bed location and the particle settling flux. Above, the concentrations saturate thus forming a plateau. Particle erosion mechanisms have been investigated in terms of competing forces within an "impulse approach". Horizontal drag versus friction first leads to a horizontal motion followed by a vertical motion resulting from vertical drag and lift versus buoyancy. Particle erosion occurs when both force balances are in favor of motion for a duration of 0.1 to 0.3 Kolmogorov time scale.

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Section: Please Cite This Article As Doi:101063/15141943mentioning

confidence: 96%

Section: Please Cite This Article As Doi:101063/15141943mentioning

confidence: 99%

Section: Please Cite This Article As Doi:101063/15141943mentioning

confidence: 99%

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Sediment erosion in zero-mean-shear turbulence

2020

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“…Oscillating grid stirred tanks have been used for many purposes in research on turbulence. Among them is the study of interactions between turbulence and solid impermeable boundaries Munro 2017, 2018a), turbulence and gas-liquid mass transfer at a free surface (Brumley and Jirka 1987;Chiapponi et al 2012;Herlina 2005;McKenna and McGillis 2004b), in stratified media (Hopfinger and Toly 1976;Thompson and Turner 1975;Verso et al 2017;Xuequan and Hopfinger 1986), or study the behavior of bubbles, cells, fibres and aggregates suspended in a turbulent liquid phase (Mahamod et al 2017;Nagami and Saito 2013;Rastello et al 2017;San et al 2017). Apart from fundamental turbulence studies, oscillating grids are used as flotation cells (Cuthbertson et al 2018;Massey et al 2012;Safari et al 2017) in tanks with various shapes (tubular, prismatic, etc.…”

Section: Introductionmentioning

confidence: 99%

Flow around an oscillating grid in water and shear-thinning polymer solution at low Reynolds number

et al. 2019

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The study of turbulence in complex fluids is of great interest in many environmental and industrial applications, in which the interactions between liquid phase rheology, turbulence, and other phenomena such as mixing or heat and mass transfer have to be understood. Oscillating grid stirred tanks have been used for many purposes in research involving turbulence. However, the mechanisms of turbulence production by the oscillating grid itself have never been studied, and oscillating grid turbulence (OGT) remained undescribed in non-Newtonian, shear-thinning, dilute polymer solutions until recently (Lacassagne et al., in Phys Fluids 31(8):083,102, 2019). The aim of this paper is to study the influence of the shear-thinning property of dilute polymer solutions (DPS), such as xanthan gum (XG), on mean flow, oscillatory flows, and turbulence around an oscillating grid. Liquid phase velocity is measured by particle image velocimetry (PIV) in a vertical plane above the central grid bar. Mean, oscillatory and turbulent components of the velocity fields are deduced by triple Hussain-Reynolds decomposition based on grid phase-resolved measurements. Outside of the grid swept region, the amplitude of oscillatory fluctuations quickly become negligible compared to that of turbulent fluctuations, and the triple and classical Reynolds decomposition become equivalent. Oscillatory jets and wakes behind the grid and their interactions are visualized. Turbulent (Reynolds) and oscillatory stresses are used to evidence a modification of oscillatory flow and turbulence intensity repartition in and around the grid swept region. Energy transfer terms between mean, oscillatory and turbulent flows are estimated and used to describe turbulence production in the grid swept region. Energy is injected by the grid into the oscillatory component. In water, it is transferred to turbulence mostly inside the grid swept region. In DPS, oscillatory flow persists outside of the grid swept zone. Energy is transferred not only to turbulence , in the grid swept region, and far from the tank's walls, but also to the mean flow, leading to an enhancement of the latter. Mean flow production and enhancement mechanisms are explainable by oscillatory jet variable symmetry and intensity, and by time-and space-variable viscosity. Backward transfer from turbulence to oscillatory flow is also evidenced in DPS. Finally, using phased root mean square (rms) values of turbulent velocity fluctuations, it is shown that in water, the decay of turbulence intensity behind an oscillating grid can be related to the decay of fixed grid turbulence for specific grid positions, a result no longer valid in DPS.

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“…Oscillating grid apparatus have been commonly used in experimental fluid mechanics since the seminal works of 20,21 . Numerous applications can be found in the literature, among which the study of interactions between turbulence and solid impermeable boundaries, 23,24 of turbulence and gas–liquid mass transfer at a free surface, 19,25‐28 in stratified media, 20,21,29,30 or to study the behavior of bubbles, cells, fibers, and flocculation aggregates suspended in a turbulent liquid phase 31‐35 . Oscillating grid stirred tanks are thus tools that allow to generate and study controlled turbulence.…”

Section: Introductionmentioning

confidence: 99%

POD analysis of oscillating grid turbulence in water and shear thinning polymer solution

et al. 2020

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Oscillating grids are frequently used with water and Newtonian fluids to generate controlled turbulence and mixing. Yet, their use with shear thinning fluids still requires experimental characterization. Proper orthogonal decomposition (POD) is applied to PIV measurements of the flow generated by an oscillating grid in water and a shear thinning dilute polymer solution (DPS) of xanthan gum. The aims are to investigate the ability of POD to isolate periodic flow structures, and to use it to describe the effects of the shear thinning property. A dominance of the low order POD modes is evidenced in DPS. The methods applied in blade stirred tanks to identify oscillatory motion fail here. However, a strong mode coupling in the grid swept region is observed, determined by the working fluid and by an underlying chaotic nature of the flow. Possibilities of reconstructing turbulence properties using high order modes are discussed.

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Steady state model and experiment for an oscillating grid turbulent two-layer stratified flow

Cited by 10 publications

References 30 publications

Sediment erosion in zero-mean-shear turbulence

Sediment erosion in zero-mean-shear turbulence

Flow around an oscillating grid in water and shear-thinning polymer solution at low Reynolds number

POD analysis of oscillating grid turbulence in water and shear thinning polymer solution

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