In this paper we propose a novel approach to solve the inverse problem of three-dimensional die design for extrudate swell, using a real-time active control scheme. To this end, we envisioned a feedback connection between the corner-line finite element method, used to predict the positions of the free surfaces of the extrudate, and the controller. The corner-line method allows for local mesh refinement

Wormlike micelles are self-assemblies of polymer chains that can break and recombine reversibly. In this paper, we derive a thermodynamically consistent two-species micro-macro model of wormlike micellar solutions by employing an energetic variational approach. The model incorporates a breakage and combination process of polymer chains into the classical micro-macro dumbbell model of polymeric fluids

Viscoelastic flows occur widely, and numerical simulations of them are important for a range of industrial applications. Simulations of viscoelastic flows are more challenging than their Newtonian counterparts due to the presence of exponential gradients in polymeric stress fields, which can lead to catastrophic instabilities if not carefully handled. A key development to overcome this issue is the

The purpose of this paper is to demonstrate how the general problem of interconversion between parallel and orthogonal superposition protocols can be treated using the kernels in a Fréchet series expansion about the base viscometric flow. Such series differ from Fréchet series expanded about the rest history which are encountered in the theory of Green-Rivlin materials and the simple fluid theory of

One of the greatest challenges in performing numerical simulations of viscoelastic flow is how to choose the model parameters in order to be able to achieve quantitative agreement with experimental measurements in benchmark geometries. In the present work, we revisit the original concepts of Reynolds (Re) and Weissenberg (Wi) numbers in order to provide means to adequately choose those parameters.

The thixotropic properties of fresh cemented tailing backfill (CTB) pastes applied in underground backfilling are investigated. Reversibility of thixotropy, equilibrium rheology, and stress decay curves of CTB pastes are discussed. A constitutive model that contains an evolution equation of structural parameter and a constitutive equation for shear stress is proposed. Modifications are made to incorporate

Shear flow is ubiquitous. Not only is it arguably the most widely-used deformation type to characterise complex fluids in rheological studies but also, in practice, the deformation most likely to occur in the great majority of flows, e.g. involving fluid transport through pipes or conduits. In steady simple shear flow the rheological properties of a complex fluid are completely characterised in just

Bubbles rising steadily in Carbopol often have an inverted teardrop shape with pointed tail, in contrast to steady bubble rise computations using simple yield stress fluid models. The cause of the pointed tail is suspected to be viscoelasticity, but another possibility is that the tail arises during the bubble formation and the shape is retained via some form of fluid memory effect (elastic, thixotropic

A suspension of elastic chains of small beads in a Newtonian fluid is a common model for a viscoelastic polymer solution. The configuration of these multibead chains is described by a distribution function that evolves according to a Liouville or Fokker–Planck equation. The evolution of these multibead-chain suspensions is described using a double bracket formulation with a Hamiltonian functional.

Lubricants can exhibit significant viscoelastic effects due to the addition of high molecular weight polymers. The overall behavior of the mixture is vastly different from a simpler Newtonian fluid. Therefore, understating the influence of viscoelasticity on the load carrying capacity of the film is essential for lubricated contacts. A new modeling technique based on lubrication theory is proposed

In this paper, the two-degree-of-freedom (2DOF) vortex-induced vibration (VIV) of a circular cylinder in shear-thinning and shear-thickening non-Newtonian power-law fluids are numerically investigated. A virtual spring-damper-mass system is employed to predict the VIV of the cylinder. A comprehensive analysis is conducted to study the influence of dimensionless parameters, including reduced velocity

The dynamic and stationary deformations of a viscoplastic drop in an axisymmetric linear viscous flow is addressed through numerical analyses for a variety of governing parameters. A variation of the integral equation method used by Toose et al. (1996, 1999) is employed. It is demonstrated that a spherical drop embedded in compressional or extensional flow, which provides viscous stresses at the interface

Nonmodal analysis typically uses square-integrated quantities to characterize amplification of disturbances. However, such measures may be misleading in viscoelastic fluids, where polymer stresses can be strongly amplified over a small region. Here, we show that when using a localized measure of disturbance amplification, spanwise-constant polymer-stress fluctuations can be more amplified than streamwise-constant

A rotating cylinder asymmetrically placed across a duct, with its axis perpendicular to the axis of the channel, has long established itself as a simple mechanism for the transport of Newtonian fluids in microfluidic channels. In the present study, the possibility of transporting viscoelastic fluids by this simple mechanism is numerically investigated using finite-volume method (FVM). For ease of analysis

Extrusion-based Additive Manufacturing techniques, such as Robocasting, produce continuous filaments to create layer-wise structures. The material properties of these structures depend on the orientation of suspended particles within the filament. This orientation can be predicted by analytical models, but those models do not exist for the paste specifically regarded in this work: A multicomponent

This work deals with the numerical modeling of spillage and debris floods as Newtonian and viscoplastic Bingham flows with free surface using mixed stabilized finite elements. The main objective is the determination of the location of the free surface of the flow. A mixed stabilized velocity/pressure finite element formulation is used and the Orthogonal Subgrid Scale stabilization (OSS) and the Split

Common viscosity models that do not consider patient-specific viscosity variations have been used in computational fluid dynamics (CFD) analyses of intracranial aneurysms (IAs). However, because blood viscosity varies among patients, these results may be unreliable. Therefore, to perform reliable CFD analyses based on realistic computational conditions, a model that can easily estimate patient-specific

This study reports the verification and first experimental validation of an advanced cut-cell finite volume immersed boundary method (IBM). This novel IBM approach was developed by Jasak at the University of Zagreb and released under the name Immersed Boundary Surface Method (IBS). It is implemented and publicly available within the open-source computational fluid dynamics framework foam-extend. In

Fluid–fluid interfaces, laden with polymers, particles or other surface-active moieties, often show a rheologically complex response to deformations, in particular when strong lateral interactions are present between these moieties. The response of the interface can then no longer be described by an isotropic surface tension alone. These “structured” soft-matter interfaces are found in many industrial

We demonstrate refinements of a simple elastic-viscous-plastic rheological model with the addition of a thixotropic term to better model rheological flow of human blood. The alteration of this model will contribute to better representation of lightly structured complex materials. The simple elastic-viscous-plastic (EVP) framework requires thixotropy for more accuracy in fitting and predicting the

We describe a customized Capillary Breakup Extensional Rheometer (CaBER) with improved dynamic performance and added features for temperature control over the range from room temperature up to 250 °C. The system is aimed at characterizing the extensional rheological behavior of weakly rate-thickening fluids that are widely utilized in the automotive industry. We examine the shear rheology and filament-thinning

In this work we present theoretical and experimental studies on the structure factor in micellar systems. Cetyl trimethyl ammonium tosilate (CTAT) solutions in absence of salts exhibit a flow behavior similar to polymer solutions, while upon an increase in the ionic strength with NaCl, their behavior changes to that of a kinetic-controlled breakage-reformation process. The relaxation mechanism thus

Natural convection in a cavity with non-uniformly heated bottom wall, partly filled with a non-Newtonian nanofluid (Cu-water) layer and partly with air layer is studied numerically in this work. The mixture of water and copper nanoparticles shows a shear-thinning rheological behavior. The nanofluid's rheological parameters, i.e. consistency and flow index, are obtained according to the solid volume

A study is presented of the instabilities that may arise in radial displacement flows of yield-stress fluid in a Hele-Shaw cell. Theoretically, the viscoplastic version of the Saffman–Taylor interfacial instability is predicted to arise when the yield-stress fluid is displaced by a Newtonian one. The interface is expected to remain stable, however, if the yield-stress fluid displaces the Newtonian

Single droplet deformation in pulsatile shear flow is numerically studied by using meso-scopic dissipative particle dynamics method. Numerical model and simulation method are fully validated with three typical cases in which transient flow behaviors are well captured. Cases in quasi-Stokes regime are first investigated with flow Reynolds number to be less than O(10−2). In early stage, droplet deforms

The present comment concerns a wrong comparison made in the above paper.

The response of non-colloidal suspensions to sudden strains and sudden changes of strain rate is explored. The matrix fluids were silicone oil and glycerol/water. A Oldroyd-B model of the suspensions augmented by a friction element gives a description of the shear stresses which agrees with experiment. Friction becomes dominant for volume fractions greater than 0.3.

We report a study on the micro-confined electroosmotic flow of an Oldroyd-B fluid over a surface having asymmetric charge modulation. We have employed a combination of regular and matched asymptotic expansion to obtain the analytical solution. We have also carried out a full numerical simulation of the physicochemical problem in order to assess the full parameter space of the problem. The analytical

Electro-thermo-convection is a typical interdisciplinary problem, that has been widely studied in terms of its physical phenomena in Newtonian fluids. As an essential supplement to the study of electrohydrodynamics, electro-thermo-convection in power-law fluids within rectangular enclosures is investigated in this paper. Two geometrical configurations are considered, namely differentially heated vertical

The sedimentation of a spherical solid particle in viscoelastic fluids was studied using a Giesekus model by development of a direct numerical simulation solver based on fully-resolved and immersed boundary methods to understand the complex non-Newtonian fluid flow and spherical particle dynamics. Two benchmark problems were modeled to evaluate the accuracy of the developed solver and excellent agreement

In recent years, there has been controversy in the literature regarding the role of viscoelasticity in determining the onset of stability for a viscoelastic thread surrounded by another viscoelastic fluid. Whereas a number of authors have found that viscoelasticity serves to destabilize the system, Patrascu and Balan (2018) obtained very different results. They considered a very simple canonical system

The temporal instability behavior of a non-Newtonian liquid jet in a compressible gas is investigated theoretically. A corotational Jeffreys model is used for describing the viscoelastic liquid state. The dispersion relation is solved by Chebyshev collocation method. Besides, the effects of compressibility of gas, Reynolds number, elasticity number, and the ratio of deformation retardation time to

Linear stability analysis is performed to study the electrohydrodynamic instability of viscoelastic jets subjected to axisymmetric (m=0) and first non-axisymmetric (m=1) perturbations in the creeping-flow limit. The viscoelastic liquid jet is under the influence of a radially applied electric field induced by a concentrically placed electrode located at a finite gap width from the jet. The leaky dielectric

We investigate the linear stability of a unidirectional flow of a suspension (blood) modeling the latter as a inhomogeneous non-Newtonian fluid in which viscosity depends on both the red blood cell concentration (RBCs) and the shear rate. We consider small vessels like arteries terminal branches, arterioles or venules, where the RBCs do not distribute uniformly on the cross section. The stability analysis

In this numerical study, an original approach to simulate non-isothermal viscoelastic fluid flows at high Weissenberg numbers is presented. Stable computations over a wide range of Weissenberg numbers are assured by using the root conformation approach in a finite volume framework on general unstructured meshes. The numerical stabilization framework is extended to consider thermo-rheological properties

We present an assessment of viscosity regularization (VR) in predicting transient flows of viscoplastic fluids (VPF). Although VR has been the most popular approach for computational studies of VPF in the last decade, the understanding of its effects on the predicted flow behaviour has remained largely qualitative. To reveal the effects of VR, we present a systematic quantitative comparison of the

We consider forcespinning (FS) of nonlinear three-dimensional rotating viscoelastic jets of Boger fluids and in the presence of gravity effect. In FS process, a fluid jet is forced through an orifice of a rotating spinneret leading to the formation of a curved jet. Applying the upper-convected Maxwell constitutive model for the stress tensor part of the governing non-Newtonian jet system and using

Adopting the form of the dynamic μ(Fr,h) basal friction law and introducing a second-order viscous term into the Saint Venant-type equations, we simulated two-dimensional granular roll waves generated in a rectangular chute applying the second-order-accurate total-variation-diminishing MacCormack scheme. Consistent with previous findings, we found that the amplitude and wavelength of the wave increased

We analyse through numerical simulations, experiments, and scaling laws the dam-break problem for viscoplastic materials. Numerically, both two and three-dimensional (2D and 3D) scenarios are considered thanks to a proposed adaptive stabilized finite element framework able to compute efficiently free surface flows of highly viscoplastic materials. We choose to focus on the Bingham model. Momentum and

We present proof-of-concept experiments to illustrate the application of viscoplastic lubrication in transport of high-concentration suspensions. The proposed transport method appears robust for a wide range of suspension concentrations. We develop a theoretical description of the flow that incorporates the significant density difference between the suspension and the lubricating fluid. We explore

A steady-state laminar flow of a viscoplastic fluid through an axisymmetric sudden pipe contraction under non-isothermal conditions has been studied numerically. Mathematical formulation of the problem is given using stream function – vorticity – temperature variables. Rheological properties of the fluid are described by the Herschel–Bulkley model, which implies an unyielded region formation in the

In this paper, the novel Tensor Diffusion approach for the numerical simulation of viscoelastic fluids is introduced based on the idea, that the extra-stress tensor in the momentum equation of the flow model can be replaced by the product of the strain-rate tensor and a (nonsymmetric) tensor-valued viscosity. As potential advantage (which can be demonstrated for fully developed channel, resp., pipe

Complex fluid–fluid interfaces determine for a large part the macroscopic material properties of foams and emulsions that appear in applications such as food, materials processing and consumer care products. As a step towards predicting these properties, a 2D axisymmetric and a 3D finite element model have been developed for simulating the dynamics of a single Newtonian drop in a Newtonian matrix fluid

Oil recovery processes depend on many factors that can be altered in order to maximize the sweeping efficiency in porous media, and one of these is the rheology behavior of the displacing agent. Furthermore, scales in the recovery process should also be considered: from the macro- to microscale systems, in which capillary forces become predominant. It is also well-known the non-Newtonian behavior of

The fundamental understanding of pore scale flow mechanisms associated with the mobilization of trapped oil ganglia during the injection of polymer solutions in porous media requires detailed analysis of viscoelastic flow through pore throats, which can be modeled as constricted capillaries. Despite the vast literature on macroscale and, more recently, microscale viscoelastic flow through contraction–expansion

In this paper we study the flow of a Bingham fluid on a curved (rectangular) pipe. Flows in this kind of geometries present secondary flows due to presence of centripetal forces in the radial direction. This so called Dean Flow has been extensively studied for Newtonian fluids. In considering a yield stress fluid in similar geometries the picture is less clear. Unfortunately, there is not an analytical

Natural mud usually exhibits non-Newtonian rheological behaviors like viscoelasticity, thixotropy and yield stress. The history of each mud sample is also an important factor influencing the rheological behavior, as the state of the clay fabric – for a same composition – is dependent on the shear stresses experienced previously by the sample. Several rheological tests including stress ramp-up, oscillatory

Rayleigh–Bénard convection (RBC) is studied in an elasto-viscoplastic (EVP) gel, the widely used and studied Carbopol gel. The transition from conductive to convective regime is determined by the Schmidt–Milverton principle which leads to a critical value of the inverse of the Yield number 1∕Yc. However, an oscillatory motion in the gel is observed below 1∕Yc≈60 when smooth and untreated walls are

The flow classification developed by Thompson and Souza Mendes [Int. J. Engng. Sci. 43 (2005) 79-105] is applied to radial and squeeze flows between two parallel disks. Based on the lubrication approximation, explicit expressions of the flow classification parameter, namely ℛ, could be obtained for those flows, and the results for power-law and Bingham fluids are presented. It is shown that 0≤ℛ≤1 in

Analytical solutions involving hypergeometric functions are presented for the fully developed laminar flow of a Non-Newtonian fluid in an annulus with a stationary or a moving inner boundary. The solutions are valid for arbitrary values of the power law index in the Couette–Poiseuille flow under consideration, and consider scenarios with and without extrema in the velocity profile, in addition to flow

Uncured styrene-butadiene rubber (SBR) can be modelled as a viscoelastic material with at least two different relaxation mechanisms. In this paper we compare multi-mode constitutive models combining two viscoelastic modes (linear and/or nonlinear) in three possible ways. Our particular choice of the two modes was inspired by models originally developed to describe the response of asphalt binders. We

We investigate the interactions between a cantilevered flexible beam and cross-flow of a viscoelastic fluid. Unlike Newtonian fluids, viscoelastic fluids exhibit elastic flow instabilities even in the absence of inertia. These elastic flow instabilities drive the oscillations of flexible structures placed in their flow path. In this work, the fluid–structure interactions between the flow of viscoelastic

In the Lattice Boltzmann Method (LBM) the viscosity is inversely proportional to the relaxation frequency. Hence, it should be possible to represent the singularity of some viscoplastic models by setting the relaxation frequency to zero. In the present paper we take full advantage of the LBM capabilities to propose an efficient and stable numerical scheme for viscoplastic fluid flow simulations invoking

The orientation distribution of tiny Brownian oblate spheroidal particles suspended in a turbulent channel flow along with their generated non-Newtonian stresses are studied numerically. The direct numerical simulation of turbulent channel flow is coupled with a direct Monte-Carlo simulator for the particles conformation. The effects of particle shape factor and the intensity of rotary Brownian motion

Motivated by the recent developments in the research of untethered microrobots for performing minimally invasive procedures inside blood vessels, we have devised a novel microfluidic experiment for studying the haemodynamics around different types of cylinders confined inside a straight, long, 270×100μm channel. Two test sections are studied: flow past a confined circular cylinder and past a confined