Elastic instabilities in pressure-driven channel flow of thixotropic-viscoelasto-plastic fluids

Castillo, Hugo A.; Wilson, Helen J.

doi:10.1016/j.jnnfm.2018.07.009

Cited by 12 publications

(32 citation statements)

References 27 publications

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“…An earlier stability analysis performed within the shear thinning White-Metzner model predicted an initially 1D base state to be linearly unstable to the growth of 2D perturbations with wavevector in the flow direction, for fluids that shear thin strongly enough, at large enough imposed pressure drops [11][12][13]. Instability has also been predicted in the shear thinning Giesekus and Phan-Thien Tanner models [14] and also, very recently, in a model of thixoelastoviscoplastic flow [15]. Instability of shear thinning polymeric solutions in pressure driven flow has recently been confirmed experimentally [16][17][18][19].…”

Section: Introductionmentioning

confidence: 85%

“…The slope of the logarithm of the amplitude of the perturbations as a function of time then gives the real part of the eigenvalue ω q . (The imaginary part of the eigenvalue instead merely represents the advection rate of the perturbations [15] and is not reported here.) The flow pattern that emerges then gives the associated eigenfunction.…”

Section: Calculation Methodsmentioning

confidence: 99%

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Linear instability of shear thinning pressure driven channel flow

Barlow

Hemingway

Clarke

et al. 2019

Journal of Non-Newtonian Fluid Mechanics

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We study theoretically pressure driven planar channel flow of shear thinning viscoelastic fluids. Combining linear stability analysis and full nonlinear simulation, we study the instability of an initially one-dimensional base state to the growth of two-dimensional perturbations with wavevector in the flow direction. We do so within three widely used constitutive models: the microscopically motivated Rolie-Poly model, and the phenomenological Johnson-Segalman and White-Metzner models. In each model, we find instability when the degree of shear thinning exceeds some level characterised by the logarithmic slope of the flow curve at its shallowest point, n = d log Σ/d logγ|min. Specifically, we find instability for n < n * , with n * ≈ 0.21, 0.11 and 0.30 in the Rolie-Poly, Johnson-Segalman and White-Metzner models respectively. Within each model, we show that the critical pressure drop for the onset of instability obeys a criterion expressed in terms of this degree of shear thinning, n, together with the derivative of the first normal stress with respect to shear stress. Both shear thinning and rapid variations in first normal stress across the channel are therefore key ingredients driving the instability. In the Rolie-Poly and Johnson-Segalman models, the underlying mechanism appears to involve the destabilisation of a quasi-interface that exists in each half of the channel, across which the normal stress varies rapidly. (The flow is not however shear banded in any parameter regime that we consider.) In the White-Metzner model, no such quasi-interface exists, but the criterion for instability nonetheless appears to follow the same form as in the Rolie-Poly and Johnson-Segalman models. This presents an outstanding puzzle concerning any possibly generic nature of the instability mechanism. We finally make some brief comments on the Giesekus model, which is rather different in its predictions from the other three. arXiv:1903.01910v3 [cond-mat.soft]

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Section: Introductionmentioning

confidence: 85%

Section: Calculation Methodsmentioning

confidence: 99%

Linear instability of shear thinning pressure driven channel flow

Barlow

Hemingway

Clarke

et al. 2019

Journal of Non-Newtonian Fluid Mechanics

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“…22 Thanks to Equation (12), eff can be assessed from suspension viscosity value provided that the other parameters are known, Equation ( 13). ( 10) A nondimensional microstructure parameter is introduced, s, which describes the relative variation of eff , Equation (14). A simple evolution law is assumed for s as a function of strain rate, Equation (15), which includes a build-up, t bu , and breakdown, t bd , characteristic time for microstructure change mechanisms.…”

Section: Thixotropic Behaviormentioning

confidence: 99%

Rheology evolution of a geopolymer precursor aqueous suspension during aging

Dusserre

Farrugia

Cutard

2020

Int J Applied Ceramic Tech

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Geopolymer‐based glass‐ceramic matrix composites can be processed at room temperature and a heat treatment below 100°C leads to matrix hardening thanks to the geopolymerization mechanisms. The stabilization of the matrix into glass‐ceramics is achieved via a post‐curing at high temperature. This paves the way of the utilization of cost‐effective liquid composite molding processes, for which all the necessary equipment is already available for processing temperature ranges related to polymer matrix composites, provided that the rheological behavior of the precursor is suitable to conveniently permeate the fibrous preform. The paper describes the thixotropic rheological behavior of a reference suspension at processing temperature (10°C‐20°C) and its evolution along aging at −18°C. The changes are interpreted in terms of geopolymerization mechanisms (dissolution and polycondensation) and suspension rheology (predominance of hydrodynamic effects at high shear rate). On this basis, a phenomenological modeling framework, combining two Krieger‐Dougherty equations, is proposed to build a relationship between the effective viscosity of the suspension and the phenomena involved during aging (dissolution of aluminosilicate particles) and shearing (microstructure scalar variable).

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“…In our previous theoretical work [9], we studied elastic instabilities in planar Poiseuille flow of thixotropic-viscoelasto-plastic fluids, and we found that insta-bility is seen when viscoelastic effects dominate. On the other hand, thixotropy has a stabilising effect.…”

Section: Introductionmentioning

confidence: 97%

“…In the present work, we use a much more realistic constitutive model, which is an extension of the model used in our previous work [9]: the generalised BMP model, which is able to predict the shear-banding phenomenon of micellar solutions, along with thixotropic, viscoelastic and plastic behaviours. We introduce this model in section 2 and show the behaviour in simple shear flow, where we illustrate the characteristic flow curve of shear-banded fluids predicted by the model in section 2.2.…”

Section: Introductionmentioning

confidence: 99%

Bulk and interfacial modes of instability in channel flow of thixotropic-viscoelasto-plastic fluids with shear-banding

Castillo

Wilson

2020

Journal of Non-Newtonian Fluid Mechanics

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We carry out a linear stability analysis of the generalised BMP model, which incorporates the shear-banding phenomenon into flows of thixotropicviscoelasto-plastic fluids: common behaviours observed in wormlike micellar solutions. We introduce a new dimensionless parameter governing shear-banding, and find that when a flow is unstable in the absence of shear-banding, this parameter has a stabilising effect. Above a critical value of the shear-banding parameter, shear bands appear in the flow gradient direction. Here two different modes of instability are observed: a bulk mode (which is the same as that seen in the absence of shear banding) and an interfacial mode. We found that the former dominates over the latter at low values of the shear-banding parameter, but the interfacial instability becomes dominant at very high values of the parameter. In particular, the interfacial modes are more unstable in flows where the low shear band has almost constant viscosity. The two modes of instability depend on different material timescales: interfacial modes become more dangerous if the interface location is near the channel wall, which is seen when the structural relaxation time is much larger than that of plasticity, while bulk modes (as seen in previous work) are highly unstable if the timescale of viscoelasticity is much longer than both those of plasticity and thixotropy.

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Elastic instabilities in pressure-driven channel flow of thixotropic-viscoelasto-plastic fluids

Cited by 12 publications

References 27 publications

Linear instability of shear thinning pressure driven channel flow

Linear instability of shear thinning pressure driven channel flow

Rheology evolution of a geopolymer precursor aqueous suspension during aging

Bulk and interfacial modes of instability in channel flow of thixotropic-viscoelasto-plastic fluids with shear-banding

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