Numerical modelling of thixotropic and viscoelastoplastic materials in complex flows

Abstract

This study is concerned with the finite element/finite volume (fe/fv) simulation of thixotropic and viscoelastoplastic material systems through two model approaches: (i) a new micellar thixotropic constitutive model for wormlike micellar systems (that introduces viscoelasticity into the network structure construction/destruction kinetic equation) and (ii) adopting a Bingham-Papanastasiou model. The computational approach is based on a hybrid parent/subcell scheme, which is cast about a semi-implicit incremental pressure correction (ipc) scheme. The appearance of plastic behaviour arises through the micellar polymeric viscosity, by increasing the zero-shear viscosity (low solvent fractions), whilst the Bingham-Papanastasiou introduces plastic features through the solvent viscosity. The characteristics of thixotropic wormlike micellar systems are represented through the class of Bautista-Manero models. Correction is incorporated, based on physical arguments for fluidity, in which absolute values of the dissipation function are adopted in complex flow, thereby accessing low-solvent fractions and high-elasticity levels. Considering elastic and plastic influences separately, solutions are compared and contrasted for contraction-expansion flow, identifying such flow field features as vortex dynamics, stress field structure, yield front patterns and enhanced pressure drop. Particular attention is paid to the influence of enhanced strain hardening that is introduced through stronger thixotropic structural features. Vortex activity decreases as either We is increased at a fixed τ 0 or τ 0 is increased at a fixed We. Exaggerated strainhardening properties are observed to have a major impact on vortex activity. Patterns and trends in normal stress difference fields reflect those in re-entrant corner vortex patterns. Yield front patterns are significantly influenced with yield stress τ 0 variation and more so than elevation in elasticity. Findings on excess pressure drop (epd) versus increased yield stress (τ 0 ) follow a linear trend. Consistently, it is evident that any variation that leads to a more solid-like behaviour produces epd enhancement. In addition, relatively more structured fluids display distinctly larger epd values throughout the τ 0 range covered.

Predictions for circular contraction-expansion flows with viscoelastoplastic & thixotropic fluids

“…Moreover, plastic-to-liquid like transition has been considered as a consequence of a dynamic structure-destruction and reformation, hence, introducing a thixotropic ingredient to explain such a response [15,22]. This recent interest in the time-dependent side of the yielding phenomenon is reflected in an increasing number of publications considering thixotropy and viscoelasticity to approximate the response of viscoelastoplastic materials in ideal and complex flows [23], fact that stands as a motivation from the present and previous works [6][7].…”

“…The theme of this predictive study is that of thixotropic-viscoelastoplastic flow in complex deformation. The constitutive equations employed reflect this and are model variants from the classes of Bautista-Manero [1][2][3][4][5][6][7][8] and . The study is conducted under a flow-rate (Q)-increase protocol, and hence, under fixed fluid relaxation-time (Maxwellian averaged, 1).…”

Convoluted models and high-Weissenberg predictions for micellar thixotropic fluids in contraction–expansion flows

“…10 b), there is clear evidence for the ultimate take up of the epd plateau at epd ∼0. 15. This is borne out by the plateaux in material functions of Fig.…”

“…This has consequences on the material properties of viscosity and elasticity. This complex constitution spurns highly complex rheological phenomena [7] , and manifests features associated with thixotropy [1] , pseudo plasticity [1][2][3][4][5] , shear banding [8][9][10][11][12][13] and yield stress [14,15] . These systems have been coined 'smart materials' , as their rheology dynamically adjusts to conform to prevailing environmental conditions.…”

Transient motions of elasto-viscoplastic thixotropic materials subjected to an imposed stress field and to stress-based free-surface boundary conditions

“…Two kinds of boundary conditions were imposed at the top: constant velocity and constant force. Among the few examples of numerical works on elasto-viscoplastic thixotropic materials are the works of Fonseca, Frey, Naccache, and de Souza Mendes (2013) , where a Maxwell based viscoelastic model is used as a basis for the inclusion of viscoplastic and thixotropic effects and ( Link, Frey, Thompson, Naccache, & de Souza Mendes, 2015;López-Aguilar et al, 2015 ) where an Oldroyd-B based viscoelastic model is the original backbone.…”