The dynamics of streaky structures in a viscoelastic pipe flow of FENE-P fluids is studied numerically. The values of Weissenberg number (Wi, polymer relaxation time over flow turn-over time) and viscosity ratios are varied to evaluate the effects of viscoelasticity in the pipe. For Reynolds numbers 3000∼3500 (based on pipe radius and maximum laminar velocity) near the transition boundary,we select

We analyse the influence of fluid yield stress on propagation of a radial (penny-shaped) hydraulic fracture in a permeable reservoir. In particular, the Herschel-Bulkley rheological model is adopted that includes yield stress and non-linearity of the shear stress. The rock is assumed to be linear elastic, and the fracture is driven by the point source fluid injection with a constant volumetric rate

Two-dimensional unsteady inertial flows of a yield stress fluid around a cylinder were studied experimentally. Carbopol aqueous gels, well-known model yield stress fluids, are used. The influence of interface conditions on vortex shedding was studied in particular by modifying the roughness of the cylinder. When wall adherence was guaranteed, it was possible to observe alternate vortex shedding similar

We investigate the entrapment condition of initially spherical and ellipsoidal Newtonian bubbles in viscoplastic materials using direct numerical simulations. For a spherical bubble, the entrapment condition depends on the balance between the buoyancy force and the force exerted by the yield stress of the viscoplastic material. For non-spherical bubbles, surface tension may yield the surrounding material

Large Eddy Simulation (LES) of turbulent non-Newtonian flows involves two additional closures, namely the Non-Newtonian SubGrid-Scale (NNSGS) stress tensor and filtered viscosity. Here, dynamic closures are proposed for NNSGS, eliminating the need for model calibration. In addition, for the primary evaluation of LES closures, two canonical case studies are designed by the extension of Newtonian forced

Co-extrusion has become the state-of-the-art process technology in nearly all application areas of polymer processing. By combining different types of polymeric materials within multilayer structures, products with a broad range of property profiles can be obtained for advanced applications. Design of co-extrusion dies and feedblock systems requires extensive knowledge of process and material behavior

The media have been reporting natural disasters frequently associated with climate change. When it comes to mudflows, the impact is substantial, especially on highly vulnerable communities. Under appropriate conditions (inclination, discharge and rheology), waves with constant amplitude, length and celerity can occur on the free surface of the flow. Such phenomenon is called roll wave, and it generally

The economic and engineering importance of additive drag reduction (DR) has provided motivation and wealth of data on the phenomena in straight conduit flows. Study into the effect of drag-reducing additives (DRAs) on complex and under-developed flows in and after bends is very limited. Novel results of DR in and around U-bends is presented in this work. Three polymer types were tested and the radii

We present a reformulation of the ‘reactive rod model’ (RRM) of Dutta and Graham (2018), a constitutive model for describing the behavior of dilute wormlike micelle solutions. The RRM treats wormlike micelle solutions as dilute suspensions of rigid Brownian rods undergoing reversible scission and growth in flow. Evolution equations for micelle orientation and stress contribution are coupled to a kinetic

Oldroyd's 1946 formulation of the constitutive equation of yield stress fluids laid the foundation of modern rheology of yield stress fluids, by considering not just the simple shear behavior of yield-stress fluids in the plastic regime, but also by prescribing a simple expression for how they behave prior to yielding and a 3D expression for how they behave beyond yielding. We discuss the implications

Oblique stretching is a special approach for the fabrication of polymer film whose product is mainly used in the optical display field, such as compensation films, retardation films, et al. Nonetheless, the previous research reports on oblique stretching processing are still lacking, and the related numerical research is almost blank. This contribution uses the FEM (finite element method) to simulate

Large eddy simulation (LES) is expected to be an efficient and accurate numerical method for predicting the behavior of non-Newtonian fluids. However, it has been reported that the LES results obtained using eddy viscosity subgrid-scale (SGS) models have a high dependency on the grid resolution for wall turbulence. In order to resolve this problem, in the present study, a mixed SGS model combining

A general framework for Maxwell-Oldroyd type differential constitutive models is examined, in which an unspecified nonlinear function of the stress tensor and rate-of-deformation tensor is incorporated into the well-known corotational version of the Jeffreys model discussed by Oldroyd. For medium amplitude simple shear deformations, the recently developed mathematical framework of medium amplitude

An extensive numerical investigation of the flow and heat transfer phenomena of a solid sphere translating in a cylindrical tube filled with FENE-P viscoelastic fluids is reported herein. The governing equations, namely, mass, momentum, energy, and viscoelastic constitutive equations, have been solved over the following ranges of conditions: Reynolds number, 1≤Re≤100, Weissenberg number, 0≤Wi≤10, polymer

A clogged waxy crude oil pipeline, entails a high pressure to de-structure the gelled oil and resume its normal operation. Our earlier work, which utilized generalized Newtonian fluid based model, demonstrated that the presence of a gas pocket in-between the gel plugs, delays pressure propagation in the downstream gel plug [L. Tikariha, L. Kumar, Pressure propagation and flow restart in the multi-plug

A new brittle-elastoviscoplastic (BEVP) fluid model is presented in this paper. This model is relatively simple to use, as it contains few material parameters and a simple fixed-point algorithm is effective for solving the coupled system of equations. The model combines some existing fundamental features such as elasticity, plasticity and brittle damage. The combination of them is based on thermodynamics

The decade following the second world war heralded the publication of a collection of important papers on non-Newtonian fluid mechanics; Oldroyd’s work featured heavily in this collection. Not only did these articles establish important results, but Oldroyd’s style and methods set the scene for subsequent work in the area, exploiting mathematical analysis to formulate problems, establish results and

This study numerically examines vortex shedding of two-dimensional viscoelastic flow over a circular cylinder at a Reynolds number of 100. The Giesekus model is selected to describe the viscoelastic constitutive relationship and investigate the combined effects of shear-thinning and elasticity. Log-conformation reformulation is employed to stabilize our numerical simulations. The parameters of the

In this paper, the intricate gas entrapment phenomenon in the non-isothermal polymer filling process is investigated via a combined finite element and discontinuous Galerkin numerical algorithm. The evolving melt interface is captured via level set method and the eXtended Pom-Pom (XPP) constitutive model is employed to describe the viscoelastic fluid. The governing equations of flow field are solved

This paper investigates the settling of a single spherical particle immersed in an initially unstructured thixo-viscoplastic fluid. The phenomenon was numerically solved using the lattice Boltzmann method (LBM) for the mass and momentum transport equations, the immersed boundary method (IBM) for the particle dynamics, and the advection-diffusion LBM for the structural parameter transport equation.

We present the study of viscous fingering in the radial hele shaw cell, using the shear-dependent rheological fluid which transitions from the Newtonian to shear thinning behaviour, at low shear rates. The experimental observations show that the characteristic features of the fingering phenomena in the case of shear-thinning flow (such as side branching, growth of second generation fingers, inhibition

LDL concentration is believed to be responsible for plaque formation that leads to atherosclerotic cardiovascular disease. We conducted this study to investigate the effects of hematocrits and LDL diameters on LDL concentration on the wall of an abdominal aortic aneurysm (AAA). The blood flow was considered to be a pulsatile and non-Newtonian flow whose viscosity was a function of hematocrits and strain

This work studies the dynamics of linear non-modal waves in viscoelastic pipe flows of FENE-P fluids using transient growth and resolvent analyses. We particularly focus on the time evolution of the amplification of the disturbance energy (using the 4th-order Runge–Kutta method) and discuss the dynamical traits of the Orr and the critical-layer mechanisms in the conformation tensor field when the transient

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

Turbulent flows of viscoplastic fluids at high Reynolds numbers have been investigated recently with direct numerical simulations (DNS) but experimental results have been limited. For this reason, we carry out an experimental study of fully turbulent flows of a yield stress fluid in a rectangular duct with a high-resolution laser doppler anemometry (LDA) setup. We employ aqueous Carbopol solutions

We review progress and open challenges for a number of problems related to the Oldroyd B model which are of current interest to the mathematical community. We discuss existence results for initial value problems and steady flows, flow stability, and the problem of understanding the asymptotics of the high Weissenberg number limit. We also discuss efforts and challenges in numerical simulation, exemplified

In this paper J.G. Oldroyd's ideas leading to the modern understanding of wall slip phenomena are discussed. The procedure proposed by Oldroyd to analyze experimental data that imply the presence of slip is illustrated to (i) determine the slip velocity as a function of wall shear stress and (ii) to recover the true rheological parameters of the material in the absence of slip. The Oldroyd method is

In this paper, we carried out an investigation of the dynamics of an air bubble rising in viscoelastic liquids with increasing volumes via volume-of-fluid based direct numerical simulations (DNS) with local adaptive mesh refinement techniques. The exponential Phan-Thien Tanner (EPTT) model is adopted for describing the rheological behaviours of the shear-thinning viscoelastic fluid. The well-known

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

The pressure to drive a Boger fluid through a long converging channel was measured as a function of flow rate. The channel geometry and flow rates were designed to avoid an upstream vortex and to maximize extensional effects, specifically, to achieve Deborah numbers up to 3 along with a minimum strain of 3. The first measurements of pressure drop were made with two Newtonian fluids, and predictions

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

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

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.