A method for reducing mean flow in oscillating-grid turbulence

McCorquodale, Mark W.; Munro, R. G.

doi:10.1007/s00348-018-2636-7

Cited by 15 publications

(29 citation statements)

References 33 publications

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“…Compared to central jets, they should spread at higher grid distances in the walltangential, grid-normal direction, and consequently be less likely to merge with their neighbours. They are thus more likely to reach the outside of the grid swept zone and to give rise to a persistent flow on the sides of the tanks, resulting in the mean recirculation structures observed in several studies (Drayton 1993;Lacassagne et al 2019;McCorquodale and Munro 2018b;McKenna and McGillis 2004a).…”

Section: About Mean Flow Generationmentioning

confidence: 94%

“…Since the ultimate interest is to achieve turbulence homogeneity, many studies of OGT use this Z h parameter as a critical minimal distance at which the grid has to be placed from the item one wants to study the interaction with turbulence. Only recently, McCorquodale and Munro (2018b) evidenced the spatial homogenization of turbulence from the grid's swept zone to the Z h region. Once the far-grid, homogeneity region is reached, turbulence properties can be described by various evolution laws, first derived by Thompson and Turner (1975) and Hopfinger and Toly (1976) and later completed by other studies (Mcdougall 1979;Nokes 1988;Shy et al 1997;Silva and Fernando 1994;Wan Mohtar 2016).…”

Section: Oscillating Grid Turbulence In Watermentioning

confidence: 99%

“…A method for reducing mean flows in OGT is to use an inner box placed inside the stirred tank to separate the wall-induced vortices from the rest of the flow (Dickinson and Long 1983;Hopfinger and Toly 1976;McCorquodale and Munro 2018b). The complementary work previously referred to (Lacassagne et al 2019) also suggests that the mean flow may be enhanced by the presence of polymer in the dilute entanglement regime.…”

Section: Oscillating Grid Turbulence In Watermentioning

confidence: 99%

“…However, the mechanisms of turbulence production by the oscillating grid itself have never been studied. It is commonly said that turbulence arises from the interaction of jets and wakes (Thompson and Turner 1975) behind grid holes and bars, but the exact interactions of these jets and wake, and the way they merge to generate homogeneous turbulence remained unobserved, even in water, until recently (McCorquodale and Munro 2018b).…”

Section: Introductionmentioning

confidence: 99%

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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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Section: About Mean Flow Generationmentioning

confidence: 94%

Section: Oscillating Grid Turbulence In Watermentioning

confidence: 99%

Section: Oscillating Grid Turbulence In Watermentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

et al. 2019

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“…In order to study thoroughly the part turbulence plays in the erosion process, we used a well-known experimental device that is the oscillating grid 7,8 . The flow produced by this device has been widely studied 1,7,[9][10][11][12] . All different studies agree in that far enough from the grid, the mean flow becomes weak enough to be negligible while turbulence appears to be almost isotropic.…”

Section: Introductionmentioning

confidence: 99%

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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PTV measurements of oscillating grid turbulence in water and polymer solutions

et al. 2020

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Particle Tracking Velocimetry (PTV) is applied to measure the flow in an oscillating grid stirred tank filled with either water or shear thinning dilute polymer solutions (DPS) of Xanthan Gum (XG). There are many interests of studying turbulence in such complex non-Newtonian fluids (e.g. in the pharmaceutical, cosmetic, or food industry), and grid stirred tanks are commonly used for fundamental studies of turbulence in Newtonian fluids. Yet the case of oscillating grid flows in shear thinning solutions has been addressed recently by Lacassagne et al. (Exp Fluids 61(1):15, Phys Fluids 31(8):083102, 2019a, b), with only a single two dimensional (2D) Particle Image Velocimetry (PIV) characterization of mean flow and turbulence properties in the central vertical plane of the tank. Here, PTV data processed by the Shake The Box algorithm allows for the time resolved, three dimensional (3D) 3 components (3C) measurement of Lagrangian velocities for a large number of tracked particles in a central volume of interest of the tank. The possibility of projecting this Lagrangian information on an Eulerian grid is explored, and projected Eulerian results are compared with 2D PIV data from the previous work. Even if the mean flow is difficult to reproduce at the lowest polymer concentrations, a good agreement is found between measured turbulent decay laws, thus endorsing the use of this 3D-PTV metrology for the study of oscillating grid turbulence in DPS. The many possibilities of further analysis offered by the 3D3C nature of the data, either in the original Lagrangian form or in the projected Eulerian one, are finally discussed. Graphic Abstract

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A method for reducing mean flow in oscillating-grid turbulence

Cited by 15 publications

References 33 publications

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

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

Sediment erosion in zero-mean-shear turbulence

PTV measurements of oscillating grid turbulence in water and polymer solutions

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