Small scale dynamics of isotropic viscoelastic turbulence

Nguyen, M. Quan; Delache, Alexandre; Simoëns, Serge; Bos, Wouter J. T.; Hajem, Mahmoud El

doi:10.1103/physrevfluids.1.083301

Cited by 19 publications

(19 citation statements)

References 52 publications

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“…In DPS, the pattern of the T ot field is more elaborated and both positive and negative regions exist, which means that energy transfer is a two-way process. This is con-sistent with the two-way flow-polymer interaction process evidenced by Nguyen et al (2016) in viscoelastic turbulence. Figure 13 summarizes Figs.…”

Section: Energy Transferssupporting

confidence: 65%

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: Energy Transferssupporting

confidence: 65%

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

et al. 2019

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“…Despite the broadband spectral behavior, EIT is here found at relatively low Re values for which no turbulence would exist in a Newtonian fluid. The structure of EIT is thus likely to be different from that of so-called viscoelastic turbulence, in which inertial turbulent scaling laws are modified by the presence of polymers [22]. Further investigation using time-resolved quantitative flow velocity measurements in the gap, such as particle image velocimetry [17], could allow characterization of the structure of transitional EIT.…”

Section: Space and Time Spectramentioning

confidence: 99%

Vortex merging and splitting: A route to elastoinertial turbulence in Taylor-Couette flow

et al. 2020

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We report experimental evidence of a new merge-split transition (MST) to elastoinertial turbulence (EIT) in Taylor-Couette flows of viscoelastic polymer solutions, caused by merging and splitting of base Taylor vortices when crossed by elastic axial waves (rotating standing waves, RSW). These vortex merging and splitting events are not due to transient behavior, finite aspect ratio, or shear-thinning behavior. They are random in nature and increase in frequency with Re; when superimposed on a RSW flow state they cause abrupt changes in the axial spatial wavelength, leading to the transition from a RSW to the EIT state. We thus identify MST as an inertial feature solely triggered by elasticity and independent of any shear-thinning behavior.

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“…Polymer chains' structures give them the ability to deform elastically and store energy at small scales, 46 which tends to truncate or modify the flow energy cascade before reaching the Kolmogorov scale. [51][52][53][54][55] Such interactions should also impact turbulence in the homogeneous isotropic case, without high shear and boundary layers effects. It has been shown from direct numerical simulations 56,57 and experiments 53,[58][59][60] that the Eulerian quantities of the bulk turbulence (strain, enstrophy, Reynolds stress, and velocity gradients fields) are strongly reduced at small scales in viscoelastic solutions.…”

Section: B Drag Reduction and Turbulence In Polymer Solutionsmentioning

confidence: 99%

Oscillating grid turbulence in shear-thinning polymer solutions

et al. 2019

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Oscillating grid apparatuses are well known and convenient tools for the fundamental study of turbulence and its interaction with other phenomena since they allow to generate turbulence supposedly homogeneous, isotropic, and free of mean shear. They could, in particular, be used to study turbulence and mass transfer near the interface between non-Newtonian liquids and a gas, as already done in air-water situations. Although frequently used in water and Newtonian fluids, oscillating grid turbulence (OGT) generation has yet been rarely applied and never characterized in non-Newtonian media. The present work consists of a first experimental characterization of the flow properties of shear-thinning polymer (Xanthan Gum, XG) solutions stirred by an oscillating grid. Various polymer concentrations are tested for a single grid stirring condition. The dilute and semidilute entanglement concentration regimes are considered. Liquid phase velocities are measured by Particle Image Velocimetry. The existing mean flow established in the tank is described and characterized, as well as turbulence properties (intensity, decay rate, length scales, isotropy, etc.). OGT in dilute polymer solutions induces an enhanced mean flow compared to water, a similar decay behavior with yet different decay rates, and enhanced turbulence large scales and anisotropy. In the semidilute regime of XG, turbulence and mean flows are essentially damped by viscosity. The evolution of mean flow and turbulence indicators leads to the definition of several polymer concentration subregimes, within the dilute one. Critical concentrations around 20 ppm and 50 ppm are found, comparable to drag reduction characteristic concentrations.

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Small scale dynamics of isotropic viscoelastic turbulence

Cited by 19 publications

References 52 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

Vortex merging and splitting: A route to elastoinertial turbulence in Taylor-Couette flow

Oscillating grid turbulence in shear-thinning polymer solutions

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