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Banaei, Arash AlizadORCID iD iconorcid.org/0000-0002-5610-2394
Publikasjoner (10 av 14) Visa alla publikasjoner
Khan, M., More, R. V., Banaei, A. A., Brandt, L. & Ardekani, A. M. (2023). Rheology of concentrated fiber suspensions with a load-dependent friction coefficient. Physical Review Fluids, 8(4), Article ID 044301.
Åpne denne publikasjonen i ny fane eller vindu >>Rheology of concentrated fiber suspensions with a load-dependent friction coefficient
Vise andre…
2023 (engelsk)Inngår i: Physical Review Fluids, E-ISSN 2469-990X, Vol. 8, nr 4, artikkel-id 044301Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

We investigate the effects of fiber aspect ratio, roughness, flexibility, and volume fraction on the rheology of concentrated suspensions in a steady shear flow using direct numerical simulations. We model the fibers as inextensible continuous flexible slender bodies with the Euler-Bernoulli beam equation governing their dynamics suspended in an incompressible Newtonian fluid. The fiber dynamics and fluid flow coupling is achieved using the immersed boundary method. In addition, the fiber surface roughness might lead to interfiber contacts, resulting in normal and tangential forces between the fibers, which follow Coulomb's law of friction. The surface roughness is modeled as hemispherical pro-trusions on the fiber surfaces. Their deformation results in a normal load-dependent friction coefficient. Our simulations accurately predict the experimentally observed shear thinning in fiber suspensions. Furthermore, we find that the suspension viscosity eta increases with increasing the volume fraction, roughness, fiber rigidity, and aspect ratio. The increase in eta is the macroscopic manifestation of a similar increase in the microscopic contact contribution to the total stress with these parameters. In addition, we observe positive and negative first N1 and second N2 normal stress differences, respectively, with |N2| < |N1|, in agreement with previous experiments. Last, we propose a modified Maron-Pierce law to quantify the reduction in the jamming volume fraction by increasing the fiber aspect ratio and roughness. Our results and analysis establish the use of fiber surface tribology to tune the suspension flow behavior.

sted, utgiver, år, opplag, sider
American Physical Society (APS), 2023
HSV kategori
Identifikatorer
urn:nbn:se:kth:diva-329864 (URN)10.1103/PhysRevFluids.8.044301 (DOI)000996373400002 ()2-s2.0-85153889564 (Scopus ID)
Merknad

QC 20230626

Tilgjengelig fra: 2023-06-26 Laget: 2023-06-26 Sist oppdatert: 2023-06-26bibliografisk kontrollert
Rahmani, M., Banaei, A. A., Brandt, L. & Martinez, D. M. (2023). Stochastic model for predicting the shape of flexible fibers in suspensions. Physical Review Fluids, 8(2), Article ID 024306.
Åpne denne publikasjonen i ny fane eller vindu >>Stochastic model for predicting the shape of flexible fibers in suspensions
2023 (engelsk)Inngår i: Physical Review Fluids, E-ISSN 2469-990X, Vol. 8, nr 2, artikkel-id 024306Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

We describe the shape of moderately flexible fibers settling under inertial conditions in dilute and semidilute suspension and examine the hydrodynamic forces on the fibers that create different fiber shapes. The analysis is based on numerical simulations, using an immersed boundary method, to couple the motion of the fibers to the fluid dynamics. The direct numerical simulation results show that while fiber curvature can have a nonmonotonic dependence on fiber concentration, fiber torsion monotonically increases with increasing the concentration of fibers. Based on the concept of splitting the total forces into a mean and a stochastic part, we propose a reduced-order, stochastic model that can, with a reasonable accuracy, model the three-dimensional fiber shapes at different fiber concentrations, flexibility, and inertia. This model also helps us understand how random hydrodynamic fluctuations and fluid-mediated forces due to the presence of neighboring fibers contribute to the total forces on the fibers and fiber shapes.

sted, utgiver, år, opplag, sider
American Physical Society (APS), 2023
HSV kategori
Identifikatorer
urn:nbn:se:kth:diva-325190 (URN)10.1103/PhysRevFluids.8.024306 (DOI)000943099400002 ()2-s2.0-85149676909 (Scopus ID)
Merknad

QC 20230411

Tilgjengelig fra: 2023-04-11 Laget: 2023-04-11 Sist oppdatert: 2023-04-11bibliografisk kontrollert
Banaei, A. A., Shahmardi, A. & Brandt, L. (2021). Numerical study of suspensions of nucleated capsules at finite inertia. Physical Review Fluids, 6(4), Article ID 044301.
Åpne denne publikasjonen i ny fane eller vindu >>Numerical study of suspensions of nucleated capsules at finite inertia
2021 (engelsk)Inngår i: Physical Review Fluids, E-ISSN 2469-990X, Vol. 6, nr 4, artikkel-id 044301Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

We study the rheology of suspensions of capsules with a rigid nucleus at negligible and finite flow inertia by means of numerical simulations. The capsule membrane is modeled as a thin Neo-Hookean hyperelastic material and the nucleus as a rigid particle with radius equal to half the radius of the undeformed spherical capsules. The fluid and solid motion are coupled with an immersed boundary method, validated for both the deformable membrane and the rigid nucleus. We examine the effect of the Reynolds number, capillary number, and volume fraction on the macroscopic properties of the suspensions, comparing with the case of capsules without nuclei. To explain the rheological measurables, we examine the mean capsule deformation, the mean orientation with respect to the flow direction, and the stress budget. The results indicate that the relative viscosity decreases with the capillary number, i.e., increasing deformability, and increases with inertia. The presence of a nucleus always reduces the membrane deformation. Capsules align more in the flow direction at higher capillary numbers and at higher volume fractions, where we also see a significant portion of them oriented with their longer deformed axis in the spanwise direction. When increasing inertia, the alignment with the flow decreases while more capsules orient in the spanwise direction. The first normal stress difference increases with the capillary number and it is always less for the nucleated capsules. Finally, the relative viscosity and the first normal stress difference increase with the capsule volume fraction, an effect more pronounced for the first normal stress difference.

sted, utgiver, år, opplag, sider
AMER PHYSICAL SOC, 2021
HSV kategori
Identifikatorer
urn:nbn:se:kth:diva-296429 (URN)10.1103/PhysRevFluids.6.044301 (DOI)000652857800002 ()2-s2.0-85104854002 (Scopus ID)
Merknad

QC 20210614

Tilgjengelig fra: 2021-06-14 Laget: 2021-06-14 Sist oppdatert: 2022-10-25bibliografisk kontrollert
Rosti, M. E., Olivieri, S., Banaei, A. A., Brandt, L. & Mazzino, A. (2020). Flowing fibers as a proxy of turbulence statistics. Meccanica (Milano. Print), 55, 357-370
Åpne denne publikasjonen i ny fane eller vindu >>Flowing fibers as a proxy of turbulence statistics
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2020 (engelsk)Inngår i: Meccanica (Milano. Print), ISSN 0025-6455, E-ISSN 1572-9648, Vol. 55, s. 357-370Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

The flapping states of a flexible fiber fully coupled to a three-dimensional turbulent flow are investigated via state-of-the-art numerical methods. Two distinct flapping regimes are predicted by the phenomenological theory recently proposed by Rosti et al. (Phys. Rev. Lett. 121:044501, 2018) the under-damped regime, where the elasticity strongly affects the fiber dynamics, and the over-damped regime, where the elastic effects are strongly inhibited. In both cases we can identify a critical value of the bending rigidity of the fiber by a resonance condition, which further provides a distinction between different flapping behaviors, especially in the under-damped case. We validate the theory by means of direct numerical simulations and find that, both for the over-damped regime and for the under-damped one, fibers are effectively slaved to the turbulent fluctuations and can therefore be used as a proxy to measure various two-point statistics of turbulence. Finally, we show that this holds true also in the case of a passive fiber, without any feedback force on the fluid.

sted, utgiver, år, opplag, sider
Springer Netherlands, 2020
Emneord
Dispersed flows, Fiber, Multiphase flows, Turbulence, Multiphase flow, Numerical methods, Dispersed flow, Flapping behavior, Phenomenological theory, Resonance condition, Three-dimensional turbulent flow, Turbulence statistics, Turbulent fluctuation, Two point statistics, Fibers
HSV kategori
Identifikatorer
urn:nbn:se:kth:diva-263285 (URN)10.1007/s11012-019-00997-2 (DOI)000512775600006 ()2-s2.0-85068170932 (Scopus ID)
Merknad

QC 20191105

Tilgjengelig fra: 2019-11-05 Laget: 2019-11-05 Sist oppdatert: 2022-06-26bibliografisk kontrollert
Alizad Banaei, A., Rahmani, M., Martinez, D. M. & Brandt, L. (2020). Inertial settling of flexible fiber suspensions. Physical Review Fluids, 5(2), Article ID 024301.
Åpne denne publikasjonen i ny fane eller vindu >>Inertial settling of flexible fiber suspensions
2020 (engelsk)Inngår i: Physical Review Fluids, E-ISSN 2469-990X, Vol. 5, nr 2, artikkel-id 024301Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

We study the inertial settling of suspensions of flexible and rigid fibers using an immersed boundary method. The fibers considered are inextensible and slender, with an aspect ratio of 20. For a single Galileo number of Ga = 160, we examine a range of dimensionless bending rigidities 0.1 < gamma < 20 and fiber concentrations 0.5 < nL(3) < 25, with n being the fiber number density and L the fiber length, that spans dilute and semidilute regimes. The settling fibers form streamers, regions where the fibers are packed and settle faster than the average settling velocity of the suspension, for nL(3) > 10. In the low-concentration regions outside the streamers, the fibers either go upward or have low settling velocities. Flexible fibers exhibit higher packing inside the streamers and smaller streamers compared to the streamers formed by the rigid fibers. Due to this higher packing, the flexible fibers settle faster compared to the rigid fibers. The formation of the streamers counterbalances the hindering of the settling velocity at higher concentrations. At higher nL(3), however, the maximum local concentration of fibers relative to a uniform distribution diminishes for both flexible and rigid fibers as the mobility of the fibers becomes limited due to the presence of other fibers in their vicinity. Due to this limited mobility, the deformation of the fibers and their settling orientation become insensitive to nL(3) for nL(3) > 7. In both the dilute and semidilute regimes, flexible fibers are more aligned with the direction perpendicular to gravity compared to rigid fibers.

sted, utgiver, år, opplag, sider
American Physical Society, 2020
HSV kategori
Identifikatorer
urn:nbn:se:kth:diva-268814 (URN)10.1103/PhysRevFluids.5.024301 (DOI)000511202700003 ()2-s2.0-85080933303 (Scopus ID)
Merknad

QC 20200221

Tilgjengelig fra: 2020-02-21 Laget: 2020-02-21 Sist oppdatert: 2024-03-15bibliografisk kontrollert
Banaei, A. A., Rosti, M. E. & Brandt, L. (2020). Numerical study of filament suspensions at finite inertia. Journal of Fluid Mechanics, 882, Article ID A5.
Åpne denne publikasjonen i ny fane eller vindu >>Numerical study of filament suspensions at finite inertia
2020 (engelsk)Inngår i: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 882, artikkel-id A5Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

We present a numerical study on the rheology of semi-dilute and concentrated filament suspensions of different bending stiffness and Reynolds number, with the immersed boundary method used to couple the fluid and solid. The filaments are considered as one-dimensional inextensible slender bodies with fixed aspect ratio, obeying the Euler-Bernoulli beam equation. To understand the global suspension behaviour we relate it to the filament microstructure, deformation and elastic energy and examine the stress budget to quantify the effect of the elastic contribution. At fixed volume fraction, the viscosity of the suspension reduces when decreasing the bending rigidity and grows when increasing the Reynolds number. The change in the relative viscosity is stronger at finite inertia, although still in the laminar flow regime, as considered here. Moreover, we find the first normal stress difference to be positive as in polymeric fluids, and to increase with the Reynolds number; its value has a peak for an intermediate value of the filament bending stiffness. The peak value is found to be proportional to the Reynolds number, moving towards more rigid suspensions at larger inertia. Moreover, the viscosity increases when increasing the filament volume fraction, and the rate of increase of the filament stress with the bending rigidity is stronger at higher Reynolds numbers and reduces with the volume fraction. We show that this behaviour is associated with the formation of a more ordered structure in the flow, where filaments tend to be more aligned and move as a compact aggregate, thus reducing the filament-filament interactions despite their volume fraction increases.

sted, utgiver, år, opplag, sider
CAMBRIDGE UNIV PRESS, 2020
Emneord
suspensions
HSV kategori
Identifikatorer
urn:nbn:se:kth:diva-266939 (URN)10.1017/jfm.2019.794 (DOI)000506238300005 ()2-s2.0-85079828455 (Scopus ID)
Merknad

QC 20200203

Tilgjengelig fra: 2020-02-03 Laget: 2020-02-03 Sist oppdatert: 2022-06-26bibliografisk kontrollert
Banaei, A. A. (2019). Simulation of deformable objects transported in fluid flow. (Doctoral dissertation). Stockholm: KTH Royal Institute of Technology
Åpne denne publikasjonen i ny fane eller vindu >>Simulation of deformable objects transported in fluid flow
2019 (engelsk)Doktoravhandling, med artikler (Annet vitenskapelig)
Abstract [en]

Deformable particles suspended in a viscous fluid can be found in many industrial and biological applications. In this thesis, two different numerical tools have been developed to simulate suspensions of capsules, thin membranes enclosing a second fluid and a rigid nucleus so to work as model for ”Eukaryotic” cells, and flexible slender bodies known as filaments/fibres. Both tools use a semi-implicit fluid flow solver with different approaches for the deformable structure. The capsule membrane is modelled as a thin hyperelastic material and the elasticity equations are solved with an accurate spectral representation of the capsule shape as a truncated number of spherical harmonics. The filaments are considered as one dimensional inextensible slender bodies obeying Euler-Bernoulli beam equations which is solved by a two-step method using finite difference discretisation. The immersed boundary method is exploited to couple the fluid and solid motion using different versions for the two different objects considered. The nucleus inside the capsules is modelled either as a second stiffer capsule or as a rigid particle. In order to avoid membrane-membrane, membrane-wall and membrane-nucleus overlapping, a short range repulsive force is implemented in terms of a potential function of the distance between the approaching objects. For the short range interactions between the filaments, both lubrication correction and collision forces are considered and it is found that the inclusion of the lubrication correction has significant effect on the rheology in shear flow. Both codes are validated against the numerical and experimental data in the literature. We study the capsule behaviour in a simple shear flow created by with two walls moving in opposite directions. The membrane obeys the Neo-Hookean constitutive equations and, in the simulations with a rigid nucleus, its radius is fixed to half the capsule initial radius. The filaments, on the other hand, are studied in 4 different flow configurations: shear flow, channel flow, settling in quiescent fluid and homogeneous isotropic turbulence. The results indicate that for single capsule, the nucleus reduces the membrane deformation significantly and changes the deformed shaped when there is negligible bending resistance of the membrane. The rheological properties of nucleated capsule suspensions result from the competition between the capsule deformation and their orientation angle and similarly to the case of single capsules, the nucleus reduces the mean deformation. By increasing the capsule volume fraction, the relative viscosity increases and capsules become more oriented in the mean flow direction. Filament suspensions in shear flow exhibit shear thinning behaviour with respect to deformability; inertia has a significant effect on the rheological properties of the suspensions as documented here. For the case of settling fibres, we document the formation of columnar structures with higher settling velocity known as streamers, which are more pronounced at higher volume fractions and for flexible fibres. For a single filament in homogeneous isotropic turbulence, two distinct regimes for the filament motion are identified with a sharp transition from one to another at a critical bending stiffness. In turbulent channel flow, we demonstrate how finite-size filaments cause considerable drag reduction, of the order of 30% for volume fractions of the order of 1.5%, and that the main averaged quantities are almost independent of the filament flexibility for the bending rigidities studied here.

sted, utgiver, år, opplag, sider
Stockholm: KTH Royal Institute of Technology, 2019. s. 72
HSV kategori
Forskningsprogram
Teknisk mekanik
Identifikatorer
urn:nbn:se:kth:diva-250721 (URN)978-91-7873-219-7 (ISBN)
Disputas
2019-06-03, F3 - Sing Sing, Lindstedtsvägen 26, Stockholm, 10:15 (engelsk)
Opponent
Veileder
Merknad

QC 20190507

Tilgjengelig fra: 2019-05-07 Laget: 2019-05-03 Sist oppdatert: 2022-06-26bibliografisk kontrollert
Rosti, M. E., Banaei, A. A., Brandt, L. & Mazzino, A. (2018). Flexible Fiber Reveals the Two-Point Statistical Properties of Turbulence. Physical Review Letters, 121(4), Article ID 044501.
Åpne denne publikasjonen i ny fane eller vindu >>Flexible Fiber Reveals the Two-Point Statistical Properties of Turbulence
2018 (engelsk)Inngår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 121, nr 4, artikkel-id 044501Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

We study the dynamics of a flexible fiber freely moving in a three-dimensional fully developed turbulent field and present a phenomenological theory to describe the interaction between the fiber elasticity and the turbulent flow. This theory leads to the identification of two distinct regimes of flapping, which we validate against direct numerical simulations fully resolving the fiber dynamics. The main result of our analysis is the identification of a flapping regime where the fiber, despite its elasticity, is slaved to the turbulent fluctuations. In this regime the fiber can be used to measure two-point statistical observables of turbulence, including scaling exponents of velocity structure functions, the sign of the energy cascade and the energy flux of turbulence, as well as the characteristic times of the eddies within the inertial range of scales. Our results are expected to have a deep impact on the experimental turbulence research as a new way, accurate and efficient, to measure two-point, and more generally multipoint, statistics of turbulence.

HSV kategori
Identifikatorer
urn:nbn:se:kth:diva-232886 (URN)10.1103/PhysRevLett.121.044501 (DOI)000439547100006 ()30095951 (PubMedID)2-s2.0-85050744852 (Scopus ID)
Merknad

QC 20180809

Tilgjengelig fra: 2018-08-09 Laget: 2018-08-09 Sist oppdatert: 2023-01-03bibliografisk kontrollert
Banaei, A. A., Loiseau, J.-C., Lashgari, I. & Brandt, L. (2017). Numerical simulations of elastic capsules with nucleus in shear flow. EUROPEAN JOURNAL OF COMPUTATIONAL MECHANICS, 26(1-2), 131-153
Åpne denne publikasjonen i ny fane eller vindu >>Numerical simulations of elastic capsules with nucleus in shear flow
2017 (engelsk)Inngår i: EUROPEAN JOURNAL OF COMPUTATIONAL MECHANICS, ISSN 1779-7179, Vol. 26, nr 1-2, s. 131-153Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

The shear-induced deformation of a capsule with a stiff nucleus, a model of eukaryotic cells, is studied numerically. The membrane of the cell and of its nucleus are modelled as a thin elastic material obeying a Neo-Hookean constitutive law. The fluid-structure coupling is obtained using an immersed boundary method. The variations induced by the presence of the nucleus on the cell deformation are investigated when varying the viscosity ratio between the inner and outer fluids, the membrane elasticity and its bending stiffness. The deformation of the eukaryotic cell is smaller than that of the prokaryotic one. The reduction in deformation increases for larger values of the capillary number. The eukaryotic cell remains thicker in itsmiddle part compared to the prokaryotic one, thus making it less flexible to pass through narrow capillaries. For a viscosity ratio of 5, the deformation of the cell is smaller than in the case of uniform viscosity. In addition, for non-zero bending stiffness of the membrane, the deformation decreases and the shape is closer to an ellipsoid. Finally, we compare the results obtained modelling the nucleus as an inner stiffer membrane with those obtained using a rigid particle.

sted, utgiver, år, opplag, sider
Taylor & Francis, 2017
Emneord
Capsule, nucleus, shear flow, immersed boundary method
HSV kategori
Identifikatorer
urn:nbn:se:kth:diva-211628 (URN)10.1080/17797179.2017.1294828 (DOI)000406001800009 ()2-s2.0-85014470144 (Scopus ID)
Forskningsfinansiär
EU, European Research Council, ERC-2013-CoG616186Swedish Research CouncilSwedish National Infrastructure for Computing (SNIC), SNIC 2016/10-36
Merknad

QC 20170809

Tilgjengelig fra: 2017-08-09 Laget: 2017-08-09 Sist oppdatert: 2022-06-27bibliografisk kontrollert
Miyauchi, S., Hayase, T., Banaei, A. A., Loiseau, J.-C., Brandt, L. & Lundell, F. (2017). Two-dimensional numerical simulation of the behavior of a circular capsule subject to an inclined centrifugal force near a plate in a fluid. JOURNAL OF FLUID SCIENCE AND TECHNOLOGY, 12(2)
Åpne denne publikasjonen i ny fane eller vindu >>Two-dimensional numerical simulation of the behavior of a circular capsule subject to an inclined centrifugal force near a plate in a fluid
Vise andre…
2017 (engelsk)Inngår i: JOURNAL OF FLUID SCIENCE AND TECHNOLOGY, ISSN 1880-5558, Vol. 12, nr 2Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

In order to examine mechanical interactions between erythrocytes and a blood vessel surface, the frictional characteristics between erythrocytes and plates in plasma have been measured by an inclined centrifuge microscope. The frictional characteristics have been properly reproduced by a numerical simulation of a rigid erythrocyte model assuming a flat bottom surface. However, validity of the assumption has not been confirmed. The purpose of this fundamental study, therefore, was to clarify the behavior of a two-dimensional circular capsule subjected to inclined centrifugal force near a plate in a fluid. An unsteady simulation was performed for various values of the angles of the inclined centrifugal force and membrane elasticity. In equilibrium states, a lubrication domain with high pressure and a large shear stress is formed between the capsule and the base plate, and the bottom surface of the capsule becomes flat with a positive attack angle. The gap distance and translational and rotational velocities increase with decreasing membrane elasticity or increasing centrifugal force angle. The attack angle increases with increasing membrane elasticity or centrifugal force angle. The results in this study qualitatively justified the assumption of the former numerical study that erythrocytes in an inclined centrifuge microscope have a flat bottom surface and its result that they have a positive attack angle in equilibrium state.

sted, utgiver, år, opplag, sider
JAPAN SOC MECHANICAL ENGINEERS, 2017
Emneord
Inclined centrifuge microscope, Frictional characteristics, Erythrocyte, Elastic capsule, Numerical simulation, Fluid-membrane interaction
HSV kategori
Identifikatorer
urn:nbn:se:kth:diva-215859 (URN)10.1299/jfst.2017jfst0015 (DOI)000411591800003 ()2-s2.0-85044219580 (Scopus ID)
Merknad

QC 20171016

Tilgjengelig fra: 2017-10-16 Laget: 2017-10-16 Sist oppdatert: 2022-06-26bibliografisk kontrollert
Organisasjoner
Identifikatorer
ORCID-id: ORCID iD iconorcid.org/0000-0002-5610-2394