| 1. |
- Chaparian, Emad, et al.
(författare)
-
An adaptive finite element method for elastoviscoplastic fluid flows
- 2019
-
Ingår i: Journal of Non-Newtonian Fluid Mechanics. - : Elsevier BV. - 0377-0257 .- 1873-2631. ; 271, s. 104148-
-
Tidskriftsartikel (refereegranskat)abstract
- Elastoviscoplastic fluids are a class of yield-stress fluids that behave like neoHookean (or viscoelastic) solids when the imposed stress is less than the yield stress whereas after yielding, their behaviour is described by a viscoplastic fluid with an additional elastic history. This exceptional behaviour has been recently observed by many yield stress fluids in rheometric tests such as waxy crude oil, Carbopol gel, etc. Moreover, interesting phenomena have been evidenced experimentally such as the presence of a negative wake and a loss of fore-aft symmetry about a settling particle which are predominantly related to the elastic behaviour of yield-stress fluids (i.e., coupling of elasticity and plasticity). Here, we present a numerical scheme based on the so-called augmented Lagrangian method for numerical simulation of elastoviscoplastic fluid flows. The method is benchmarked by two rheometric flows: Poiseuille and circular Couette flows for which analytical solutions are derived. Moreover, anisotropic adaptive mesh procedure (which was previously introduced for viscoplastic fluid flows by Saramito and Roquet, Comput. Meth. Appl. Mech. Eng., vol. 190, 2001, pp. 5391-5412) is coupled to obtain a fine resolution of the yield surfaces. Finally, the presented method is applied to study more complex flows: elastoviscoplastic fluid flow in a wavy channel.
|
|
| 2. |
- De Vita, Francesco, et al.
(författare)
-
Elastoviscoplastic flows in porous media
- 2018
-
Ingår i: Journal of Non-Newtonian Fluid Mechanics. - : Elsevier. - 0377-0257 .- 1873-2631. ; 258, s. 10-21
-
Tidskriftsartikel (refereegranskat)abstract
- We investigate the elastoviscoplastic flow through porous media by numerical simulations. We solve the Navier–Stokes equations combined with the elastoviscoplastic model proposed by Saramito for the stress tensor evolution [1]. In this model, the material behaves as a viscoelastic solid when unyielded, and as a viscoelastic Oldroyd-B fluid for stresses higher than the yield stress. The porous media is made of a symmetric array of cylinders, and we solve the flow in one periodic cell. We find that the solution is time-dependent even at low Reynolds numbers as we observe oscillations in time of the unyielded region especially at high Bingham numbers. The volume of the unyielded region slightly decreases with the Reynolds number and strongly increases with the Bingham number; up to 70% of the total volume is unyielded for the highest Bingham numbers considered here. The flow is mainly shear dominated in the yielded region, while shear and elongational flow are equally distributed in the unyielded region. We compute the relation between the pressure drop and the flow rate in the porous medium and present an empirical closure as function of the Bingham and Reynolds numbers. The apparent permeability, normalized with the case of Newtonian fluids, is shown to be greater than 1 at low Bingham numbers, corresponding to lower pressure drops due to the flow elasticity, and smaller than 1 for high Bingham numbers, indicating larger dissipation in the flow owing to the presence of the yielded regions. Finally we investigate the effect of the Weissenberg number on the distribution of the unyielded regions and on the pressure gradient.
|
|
| 3. |
- Pietrzyk, Kyle, et al.
(författare)
-
Flow around a squirmer in a shear-thinning fluid
- 2019
-
Ingår i: Journal of Non-Newtonian Fluid Mechanics. - : Elsevier. - 0377-0257 .- 1873-2631. ; 268, s. 101-110
-
Tidskriftsartikel (refereegranskat)abstract
- Many biological fluids display shear-thinning rheology, where the viscosity decreases with an increasing shear rate. To better understand how this non-Newtonian rheology affects the motion of biological and artificial micro swimmers, recent efforts have begun to seek answers to fundamental questions about active bodies in shear-thinning fluids. Previous analyses based on a squirmer model have revealed non-trivial variations of propulsion characteristics in a shear-thinning fluid via the reciprocal theorem. However, the reciprocal theorem approach does not provide knowledge about the flow surrounding the squirmer. In this work, we fill in this missing information by calculating the non-Newtonian correction to the flow analytically in the asymptotic limit of small Carreau number. In particular, we investigate the local effect due to viscosity reduction and the non-local effect due to induced changes in the flow; we then quantify their relative importance to locomotion in a shear-thinning fluid. Our results demonstrate cases where the non-local effect can be more significant than the local effect. These findings suggest that caution should be exercised when developing physical intuition from the local viscosity distribution alone around a swimmer in a shear-thinning fluid.
|
|
| 4. |
- Rosti, Marco E., et al.
(författare)
-
Suspensions of deformable particles in a Couette flow
- 2018
-
Ingår i: Journal of Non-Newtonian Fluid Mechanics. - : ELSEVIER SCIENCE BV. - 0377-0257 .- 1873-2631. ; 262, s. 3-11
-
Tidskriftsartikel (refereegranskat)abstract
- We consider suspensions of deformable particles in a Newtonian fluid by means of fully Eulerian numerical simulations with a one-continuum formulation. We study the rheology of the visco-elastic suspension in plane Couette flow in the limit of vanishing inertia and examine the dependency of the effective viscosity mu on the solid volume-fraction Phi, the capillary number Ca, and the solid to fluid viscosity ratio K. The suspension viscosity decreases with deformation and applied shear (shear-thinning) while still increasing with volume fraction. We show that mu collapses to an universal function, mu(Phi(e)), with an effective volume fraction Phi(e), lower than the nominal one owing to the particle deformation. This universal function is well described by the Eilers fit, which well approximate the rheology of suspension of rigid spheres at all O. We provide a closure for the effective volume fraction Phi(e) as function of volume fraction Phi and capillary number Ca and demonstrate it also applies to data in literature for suspensions of capsules and red-blood cells. In addition, we show that the normal stress differences exhibit a non-linear behavior, with a similar trend as in polymer and filament suspensions. The total stress budgets reveals that the particle-induced stress contribution increases with the volume fraction Phi and decreases with deformability.
|
|
| 5. |
- Wang, Yuli, et al.
(författare)
-
Impact of viscoelastic droplets
- 2017
-
Ingår i: Journal of Non-Newtonian Fluid Mechanics. - : Elsevier. - 0377-0257 .- 1873-2631. ; 243, s. 38-46
-
Tidskriftsartikel (refereegranskat)abstract
- We conduct numerical experiments on viscoelastic droplets hitting a flat solid surface. The results present time-resolved non-Newtonian stresses acting in the droplet. Comparing with the simulation of the impact of a Newtonian droplet, the effects of viscoelasticity on droplet behaviors such as splashing, the maximum spreading diameter and deformation are analyzed. With detailed information on the contact line region, we demonstrate how the contact line behaves according to the transition of the fluid property from elasticity dominated to shear-thinning dominated when a droplet expands and contracts on the substrate. The propose of this work is to discuss whether and how the elasticity in an impinging droplet takes effect.
|
|
| 6. |
- Ingelsten, Simon, 1990, et al.
(författare)
-
A Lagrangian-Eulerian framework for simulation of transient viscoelastic fluid flow
- 2019
-
Ingår i: Journal of Non-Newtonian Fluid Mechanics. - : Elsevier BV. - 0377-0257. ; 266, s. 20-32
-
Tidskriftsartikel (refereegranskat)abstract
- A novel framework for simulation of transient viscoelastic fluid flow is proposed. The viscoelastic stresses are calculated at Lagrangian nodes which are distributed in the computational domain and convected by the fluid. The coupling between the constitutive equation and the fluid momentum equations is established through robust interpolation with radial basis functions. The framework is implemented in a finite volume based flow solver that combines an octree background grid with immersed boundary techniques. Since the distribution of the Lagrangian node set is performed entirely based on spatial information from the fluid solver, the ability to simulate flows in complex geometries is therefore as general as for the fluid solver itself. In the Lagrangian formulation the discretization of the convective terms in the constitutive equations is avoided. No re-formulation of the constitutive equation is required for stable solutions. Numerical experiments are performed of UCM and Oldroyd-B fluids in a channel flow and of a four mode PTT fluid in a confined cylinder flow. The computed flow quantities consistently converge and agree excellently with analytical and numerical data for fully developed and transient flow.
|
|
| 7. |
- Johnson, Tomas, 1979, et al.
(författare)
-
Simulation of the spherical orientation probability distribution of paper fibers in an entire suspension using immersed boundary methods
- 2016
-
Ingår i: Journal of Non-Newtonian Fluid Mechanics. - : Elsevier BV. - 0377-0257. ; 229, s. 1-7
-
Tidskriftsartikel (refereegranskat)abstract
- A numerical model based on the Fokker–Planck equation for studying the orientation of paper fibers in a suspension is presented. The model is implemented in a finite volume framework. The rotational operators are discretized on a triangulated half sphere and the spatial operators are discretized on a Cartesian octree grid, where internal walls are handled with immersed boundary methods. Transient solutions of the two dimensional fiber orientation distribution are computed in the entire fluid domain. This is in contrast to earlier approaches that either only compute along streamlines or one dimensional projected orientations. The fibers are assumed to have negligible inertia and thus to follow the fluid perfectly and to be evenly distributed. A head-box geometry relevant for paper forming is used to exemplify the usefulness of the method. The influence of translational and rotational diffusion is included in the presented method.
|
|
| 8. |
- Zhong, Lijie, et al.
(författare)
-
Determination of free and esterified carotenoid composition in rose hip fruit by HPLC-DAD-APCI+-MS
- 2016
-
Ingår i: Food Chemistry. - : Elsevier BV. - 0308-8146 .- 1873-7072. ; 210, s. 541-550
-
Tidskriftsartikel (refereegranskat)abstract
- Rose hip fruit, which contains high concentration of carotenoids is commonly used for different food products in Europe and it is considered to have medical properties. In this study, a simple, rapid and efficient HPLC-DAD-APCI+-MS method was developed and applied to identify and quantify the carotenoids in rose hip fruit of four rose species, including both unsaponified and saponified extract. In the unsaponified extract 23 carotenoid esters were detected, in which either rubixanthin ester or violaxanthin ester was the dominant component of the ester composition. In the saponified extract 21 carotenoids, including 11 xanthophylls and 10 carotenes were detected. This is the first time the total carotenoid composition, including the carotenoid esters in rose hip fruit were identified and quantified. This work reveals the potential of rose hip fruit to be utilized as a healthy dietary material and give chemical information for the possible future development in the pharmacology field.
|
|
| 9. |
- Mandova, H., et al.
(författare)
-
Possibilities for CO2 emission reduction using biomass in European integrated steel plants
- 2018
-
Ingår i: Biomass and Bioenergy. - : Elsevier BV. - 0961-9534 .- 1873-2909. ; 115, s. 231-243
-
Tidskriftsartikel (refereegranskat)abstract
- Iron and steel plants producing steel via the blast furnace-basic oxygen furnace (BF-BOF) route constitute among the largest single point CO2 emitters within the European Union (EU). As the iron ore reduction process in the blast furnace is fully dependent on carbon mainly supplied by coal and coke, bioenergy is the only renewable that presents a possibility for their partial substitution. Using the BeWhere model, this work optimised the mobilization and use of biomass resources within the EU in order to identify the opportunities that bioenergy can bring to the 30 operating BF-BOF plants. The results demonstrate competition for the available biomass resources within existing industries and economically unappealing prices of the bio-based fuels. A carbon dioxide price of 60 € t−1 is required to substitute 20% of the CO2 emissions from the fossil fuels use, while a price of 140 € t−1 is needed to reach the maximum potential of 42%. The possibility to use organic wastes to produce hydrochar would not enhance the maximum emission reduction potential, but it would broaden the available feedstock during the low levels of substitution. The scope for bioenergy integration is different for each plant and so consideration of its deployment should be treated individually. Therefore, the EU-ETS (Emission Trading System) may not be the best policy tool for bioenergy as an emission reduction strategy for the iron and steel industry, as it does not differentiate between the opportunities across the different steel plants and creates additional costs for the already struggling European steel industry. © 2018 The Authors
|
|
