| 1. |
- Abdulrazaq, Muhammed, et al.
(författare)
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Numerical modelling of the extensional dynamics in elastoviscoplastic fluids
- 2023
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Ingår i: Journal of Non-Newtonian Fluid Mechanics. - : Elsevier BV. - 0377-0257 .- 1873-2631. ; 318
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Tidskriftsartikel (refereegranskat)abstract
- The extensional dynamics of an elasto-viscoplastic (EVP) fluid is studied by means of numerical simulations modelling an experimental configuration. Specifically, we track the interface between the EVP material and the Newtonian medium using an algebraic volume of fluid method (MTHINC-VOF) and employ a fully Eulerian immersed boundary method (IBM) to model the motion of the piston responsible for the extension of the material. We investigate the role of different values of the yield stress, surface tension at the interface between the EVP material and the surrounding fluid, polymer viscosity ratio, and extension rates on the necking thickness of the material, extensional viscosity, and yielding of the material for two sets of parameter with low and high elasticity. The results of the simulations reveal that when the yield stress of the EVP material is much larger than the viscous stresses, the material undergoes an elastic deformation, regardless of the selected values of the extension rate, interfacial forces, and viscosity ratio. Moreover, by increasing the ratio of the polymeric viscosity to the total viscosity of the system, the EVP material produces stronger strain hardening and reaches the minimum resolvable width sooner. Specific and novel to our study, we show that interfacial forces cannot be ignored when the surface tension coefficient is such that a Capillary number based on the extensional rate is of order 1. For large values of the surface tension coefficient, the EVP material fails sooner, with a clear deviation from the exponential reduction in the neck thickness. Moreover, our results suggest that the role of the yield stress value on the dynamics of the material is more pronounced at lower elasticity.
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| 2. |
- Bazesefidpar, Kazem, et al.
(författare)
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Numerical simulation of the coalescence-induced polymeric droplet jumping on superhydrophobic surfaces
- 2022
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Ingår i: Journal of Non-Newtonian Fluid Mechanics. - : Elsevier BV. - 0377-0257 .- 1873-2631. ; 307
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Tidskriftsartikel (refereegranskat)abstract
- Self-propelled jumping of two polymeric droplets on superhydrophobic surfaces is investigated by three-dimensional direct numerical simulations. Two identical droplets of a viscoelastic fluid slide, meet and coalesce on a surface with contact angle 180 degrees. The droplets are modelled by the Giesekus constitutive equation, introducing both viscoelasticity and a shear-thinning effects. The Cahn-Hilliard Phase-Field method is used to capture the droplet interface. The simulations capture the spontaneous coalescence and jumping of the droplets. The effect of elasticity and shear-thinning on the coalescence and jumping is investigated at capillary-inertial and viscous regimes. The results reveal that the elasticity of the droplet changes the known capillary-inertial velocity scaling of the Newtonian drops at large Ohnesorge numbers; the resulting viscoelastic droplet jumps from the surface at larger Ohnesorge numbers than a Newtonian drop, when elasticity amplifies visible shape oscillations of the merged droplet. The numerical results show that polymer chains are stretched during the coalescence and prior to the departure of two drops, and the resulting elastic stresses at the interface induce the jumping of the liquid out of the surface. This study shows that viscoelasticity, typical of many biological and industrial applications, affects the droplet behaviour on superhydrophobic and self-cleaning surfaces.
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| 3. |
- Chaparian, Emad, et al.
(författare)
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Particle migration in channel flow of an elastoviscoplastic fluid
- 2020
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Ingår i: Journal of Non-Newtonian Fluid Mechanics. - : Elsevier B.V.. - 0377-0257 .- 1873-2631. ; 284
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Tidskriftsartikel (refereegranskat)abstract
- We study the dynamics of a neutrally buoyant rigid sphere carried by an elastoviscoplastic fluid in a pressure-driven channel flow numerically. The yielding to flow is marked by the yield stress which splits the flow into two main regions: the core unyielded region and two sheared yielded regions close to the walls. The particles which are initially in the plug region are observed to translate with the same velocity as the plug without any rotation/migration. Keeping the Reynolds number fixed, we study the effect of elasticity (Weissenberg number) and plasticity (Bingham number) of the fluid on the particle migration inside the sheared regions. In the viscoelastic limit, in the range of studied parameters (low elasticity), inertia is dominant and the particle finds its equilibrium position between the centreline and the wall. The same happens in the viscoplastic limit, yet the yield surface plays the role of centreline. However, the combination of elasticity and plasticity of the suspending fluid (elastoviscoplasticity) trigger particle-focusing: in the elastoviscoplastic flow, for a certain range of Weissenberg numbers (≈0.5), isolated particles migrate all the way to the centreline by entering into the core plug region. This behaviour suggests a particle-focusing process for inertial regimes which was not previously found in a viscoelastic or viscoplastic carrying fluid.
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| 4. |
- Fallahjoybari, Nima, et al.
(författare)
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Large eddy simulation of turbulent pulp flow in a channel
- 2020
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Ingår i: Journal of Non-Newtonian Fluid Mechanics. - : Elsevier BV. - 0377-0257 .- 1873-2631. ; 285
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Tidskriftsartikel (refereegranskat)abstract
- Large eddy simulation (LES) of turbulent flow of concentrated fiber suspension or pulp is carried out to investigate the flow and turbulence structures in a channel. The simulations are carried out for the turbulent flow of Eucalyptus pulp suspension using OpenFOAM for three fiber concentrations (c = 1.5, 2.0 and 2.5) and six different Reynolds numbers (6 <= Re-s <= 16,600). It is observed that the variation in flow regime is similar in the two lower fiber concentrations while the flow regime is highly affected by fiber concentration for c = 2.5. Visualizations of vortical structures for different Reynolds numbers and fiber concentrations are used to investigate different flow regimes. Variation of apparent viscosity with Reynolds number and fiber concentration is also presented to show its effect on the turbulent properties of fiber suspension flow. It is shown that the deviation of turbulent velocity profile from that of a Newtonian flow increases with an increase in Reynolds number and fiber concentration. Also, the extend of buffer layer increases at higher Re. Using the calculated turbulent velocity profile, the values of constant in logarithmic velocity profile is proposed for fiber suspension. Finally, a discussion is presented on the variation of turbulent intensities and Reynolds stress with Reynolds number and fiber concentration.
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| 5. |
- Ingelsten, Simon, 1990, et al.
(författare)
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Computationally efficient viscoelastic flow simulation using a Lagrangian-Eulerian method and GPU-acceleration
- 2020
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Ingår i: Journal of Non-Newtonian Fluid Mechanics. - : Elsevier BV. - 0377-0257. ; 279
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Tidskriftsartikel (refereegranskat)abstract
- A recently proposed Lagrangian-Eulerian method for viscoelastic flow simulation is extended to high performance calculations on the Graphics Processing Unit (GPU). The two most computationally intensive parts of the algorithm are implemented for GPU calculation, namely the integration of the viscoelastic constitutive equation at the Lagrangian nodes and the interpolation of the resulting stresses to the cell centers of the Eulerian grid. In the original CPU method, the constitutive equations are integrated with a second order backward differentiation formula, while with the proposed GPU method the implicit Euler method is used. To allow fair comparison, the latter is also implemented for the CPU. The methods are validated for two flows, a planar Poiseuille flow of an upper-convected Maxwell fluid and flow past a confined cylinder of a four-mode Phan Thien Tanner fluid, with identical results. The calculation times for the methods are compared for a range of grid resolutions and numbers of CPU threads, revealing a significant reduction of the calculation time for the proposed GPU method. As an example, the total simulation time is roughly halved compared to the original CPU method. The integration of the constitutive equation itself is reduced by a factor 50 to 250 and the unstructured stress interpolation by a factor 15 to 60, depending on the number of CPU threads used.
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| 6. |
- Ingelsten, Simon, 1990, et al.
(författare)
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Simulation of viscoelastic squeeze flows for adhesive joining applications
- 2022
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Ingår i: Journal of Non-Newtonian Fluid Mechanics. - : Elsevier BV. - 0377-0257. ; 300
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Tidskriftsartikel (refereegranskat)abstract
- A backwards-tracking Lagrangian–Eulerian method is used to simulate planar viscoelastic squeeze flow. The momentum and continuity equations are discretized with the finite volume method and implicit immersed boundary conditions are used to describe objects in the domain. The viscoelastic squeeze flow, which involves moving solid geometry as well as free surface flow, is chosen for its relevance in industrial applications, such as adhesive parts assembly and hemming. The main objectives are to validate the numerical method for such flows and to outline the grid resolution dependence of important flow quantities. The main part of the study is performed with the Oldroyd-B model, for which the grid dependence is assessed over a wide range of Weissenberg numbers. An important conclusion is that the load exerted on the solids can be predicted with reasonable accuracy using a relatively coarse grid. Furthermore, the results are found to be in excellent agreement with theoretical predictions as well as in qualitative resemblance with numerical results from the literature. The effects of different viscoelastic properties are further investigated using the PTT model, revealing a strong influence of shear-thinning for moderate Weissenberg numbers. Finally, a reverse squeeze flow is simulated, highlighting important aspects in the context of adhesive joining applications.
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| 7. |
- Sarabian, Mohammad, et al.
(författare)
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Interface-resolved simulations of the confinement effect on the sedimentation of a sphere in yield-stress fluids
- 2022
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Ingår i: Journal of Non-Newtonian Fluid Mechanics. - : Elsevier BV. - 0377-0257 .- 1873-2631. ; 303, s. 104787-
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Tidskriftsartikel (refereegranskat)abstract
- We perform three-dimensional numerical simulations to investigate the confinement effect on the sedimen-tation of a single sphere in an otherwise quiescent yield stress fluid, in the presence of finite elasticity and weak inertia. The carrier fluid is modeled using the elastoviscoplastic constitutive laws proposed by Saramito (2009). The additional elastic stress tensor is fully coupled with the flow equation, while the rigid particle is represented by an immersed boundary method. The simulations show the faster relaxation of the fluid velocity and the progressive translation of the location of the negative wake downstream of the sphere as the bounding walls are brought closer to the particle. Moreover, the sphere drag decreases by increasing the particle-wall distance. We show that the confinement ratio (ratio of the gap between rigid confining walls and the sphere radius) reaches a critical value beyond which the wall-effect on the particle and flow dynamics becomes negligible. The key finding here is that the critical confinement ratio and the maximum variation of the Stokes drag with confinement ratio are weakly dependent on the level of material elasticity and plasticity for a certain range of material parameters. Finally, we propose an expression for the Stokes drag coefficient, as a function of material plasticity and confinement ratio.
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| 8. |
- Sedaghat, M. H., et al.
(författare)
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Three-dimensional simulation of mucociliary clearance under the ciliary abnormalities
- 2023
-
Ingår i: Journal of Non-Newtonian Fluid Mechanics. - : Elsevier B.V.. - 0377-0257 .- 1873-2631. ; 316
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Tidskriftsartikel (refereegranskat)abstract
- In this study three-dimensional computational model of a segment of bronchial airway surface liquid has been investigated to study the effect of various cilia abnormalities on mucociliary clearance (MCC), which was reported in common respiratory diseases. Numerical simulations have been devoted to studying a two-layer fluid model of the airway surface liquid (ASL) consisting of a Newtonian lower periciliary liquid (PCL) layer and a nonlinear viscoelastic upper mucus layer. The time-dependent governing and constitutive equations have been discretized and solved by a finite difference projection method on a staggered grid. The immersed boundary method has also been employed to study the effect of cilia propulsive effect on ASL. Numerical results have been devoted to investigating the influence of various cilia abnormalities, such as phase difference between cilia, cilia beat pattern, cilia beat frequency, cilia lattice geometry, missing cilia regions, and cilia density on MCC. The mucus was modeled as a nonlinear viscoelastic fluid in 3D geometry. Numerical results show that some cilia abnormalities such as cilia density, cilia beat pattern, and cilia beat frequency have a dominant effect on MCC and some abnormalities such as missing cilia regions and phase differences between cilia have a moderate influence on that. Results also show the negligible impact of cilia lattice geometry on mucus flow.
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