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Rosén, Tomasorcid.org/0000-0002-2346-7063

Open this publication in new window or tab >>Orientational dynamics of a triaxial ellipsoid in simple shear flow: Influence of inertia### Rosén, Tomas

### Kotsubo, Yusuke

### Aidun, Cyrus K.

### Do-Quang, Minh

PrimeFaces.cw("AccordionPanel","widget_formSmash_j_idt184_0_j_idt188_some",{id:"formSmash:j_idt184:0:j_idt188:some",widgetVar:"widget_formSmash_j_idt184_0_j_idt188_some",multiple:true}); ### Lundell, Fredrik

PrimeFaces.cw("AccordionPanel","widget_formSmash_j_idt184_0_j_idt188_otherAuthors",{id:"formSmash:j_idt184:0:j_idt188:otherAuthors",widgetVar:"widget_formSmash_j_idt184_0_j_idt188_otherAuthors",multiple:true}); Show others...PrimeFaces.cw("SelectBooleanButton","widget_formSmash_j_idt184_0_j_idt188_j_idt202",{id:"formSmash:j_idt184:0:j_idt188:j_idt202",widgetVar:"widget_formSmash_j_idt184_0_j_idt188_j_idt202",onLabel:"Hide others...",offLabel:"Show others..."}); 2017 (English)In: Physical review. E, ISSN 2470-0045, E-ISSN 2470-0053, Vol. 96, no 1, article id 013109Article in journal (Refereed) Published
##### Abstract [en]

##### Place, publisher, year, edition, pages

AMER PHYSICAL SOC, 2017
##### National Category

Physical Sciences
##### Identifiers

urn:nbn:se:kth:diva-211604 (URN)10.1103/PhysRevE.96.013109 (DOI)000405715200007 ()2-s2.0-85026512840 (Scopus ID)
#####

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#####

##### Funder

ÅForsk (Ångpanneföreningen's Foundation for Research and Development)
##### Note

KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.

KTH, School of Engineering Sciences (SCI), Mechanics.

KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.

The motion of a single ellipsoidal particle in simple shear flow can provide valuable insights toward understanding suspension flows with nonspherical particles. Previously, extensive studies have been performed on the ellipsoidal particle with rotational symmetry, a so-called spheroid. The nearly prolate ellipsoid (one major and two minor axes of almost equal size) is known to perform quasiperiodic or even chaotic orbits in the absence of inertia. With small particle inertia, the particle is also known to drift toward this irregular motion. However, it is not previously understood what effects from fluid inertia could be, which is of highest importance for particles close to neutral buoyancy. Here, we find that fluid inertia is acting strongly to suppress the chaotic motion and only very weak fluid inertia is sufficient to stabilize a rotation around themiddle axis. Themechanism responsible for this transition is believed to be centrifugal forces acting on fluid, which is dragged along with the rotational motion of the particle. With moderate fluid inertia, it is found that nearly prolate triaxial particles behave similarly to the perfectly spheroidal particles. Finally, we also are able to provide predictions about the stable rotational states for the general triaxial ellipsoid in simple shear with weak inertia.

QC 20170814

Available from: 2017-08-14 Created: 2017-08-14 Last updated: 2017-08-14Bibliographically approvedOpen this publication in new window or tab >>Angular dynamics of non-spherical particles in linear flows related to production of biobased materials### Rosén, Tomas

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##### Abstract [en]

##### Place, publisher, year, edition, pages

Stockholm: KTH Royal Institute of Technology, 2016. p. 134
##### Series

TRITA-MEK, ISSN 0348-467X ; 2016:14
##### Keywords

Fluid mechanics, dispersed particle flows, inertia, non-linear dynamics, rotary diffusion, characterization techniques
##### National Category

Fluid Mechanics and Acoustics
##### Identifiers

urn:nbn:se:kth:diva-193124 (URN)978-91-7729-139-8 (ISBN)
##### Public defence

2016-10-28, F2, Lindstedsvägen 26, Stockholm, 10:30 (English)
##### Opponent

### Butler, Jason E.

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##### Supervisors

### Lundell, Fredrik

### Söderberg, Daniel

### Do-Quang, Minh

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##### Note

KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center. KTH, School of Engineering Sciences (SCI), Mechanics. KTH Royal Institute of Technology.

Dispersed particle flows are encountered in many biological, geophysical but also in industrial situations, e.g. during processing of materials. In these flows, the particles usually are non-spherical and their angular dynamics play a crucial role for the final material properties. Generally, the angular dynamics of a particle is dependent on the local flow in the frame-of-reference of this particle. In this frame, the surrounding flow can be linearized and the linear velocity gradient will determine how the particle rotates. In this thesis, the main objective is to improve the fundamental knowledge of the angular dynamics of non-spherical particles related to two specific biobased material processes.

Firstly, the flow of suspended cellulose fibers in a papermaking process is used as a motivation. In this process, strong shear rates close to walls and the size of the fibers motivates the study of inertial effects on a single particle in a simple shear flow. Through direct numerical simulations combined with a global stability analysis, this flow problem is approached and all stable rotational states are found for spheroidal particles with aspect ratios ranging from moderately slender fibers to thin disc-shaped particles.

The second material process of interest is the production of strong cellulose filaments produced through hydrodynamic alignment and assembly of cellulose nanofibrils (CNF). The flow in the preparation process and the small size of the particles motivates the study of alignment and rotary diffusion of CNF in a strain flow. However, since the particles are smaller than the wavelength of visible light, the dynamics of CNF is not easily captured with standard optical techniques. With a new flow-stop experiment, rotary diffusion of CNF is measured using Polarized optical microscopy. This process is found to be quite complicated, where short-range interactions between fibrils seem to play an important role. New time-resolved X-ray characterization techniques were used to target the underlying mechanisms, but are found to be limited by the strong degradation of CNF due to the radiation.

Although the results in this thesis have limited direct applicability, they provide important fundamental stepping stones towards the possibility to control fiber orientation in flows and can potentially lead to new tailor-made materials assembled from a nano-scale.

University of Florida.

KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center. KTH, School of Engineering Sciences (SCI), Mechanics.

KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.

KTH, School of Engineering Sciences (SCI), Mechanics, Physicochemical Fluid Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.

QC 20160929

Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2016-09-29Bibliographically approvedOpen this publication in new window or tab >>Angular velocity of a sphere in a simple shear at small Reynolds number### Meibohm, J.

### Candelier, F.

### Rosén, Tomas

### Einarsson, J.

PrimeFaces.cw("AccordionPanel","widget_formSmash_j_idt184_2_j_idt188_some",{id:"formSmash:j_idt184:2:j_idt188:some",widgetVar:"widget_formSmash_j_idt184_2_j_idt188_some",multiple:true}); ### Lundell, Fredrik

### Mehlig, B.

PrimeFaces.cw("AccordionPanel","widget_formSmash_j_idt184_2_j_idt188_otherAuthors",{id:"formSmash:j_idt184:2:j_idt188:otherAuthors",widgetVar:"widget_formSmash_j_idt184_2_j_idt188_otherAuthors",multiple:true}); Show others...PrimeFaces.cw("SelectBooleanButton","widget_formSmash_j_idt184_2_j_idt188_j_idt202",{id:"formSmash:j_idt184:2:j_idt188:j_idt202",widgetVar:"widget_formSmash_j_idt184_2_j_idt188_j_idt202",onLabel:"Hide others...",offLabel:"Show others..."}); 2016 (English)In: PHYSICAL REVIEW FLUIDS, ISSN 2469-990X, Vol. 1, no 8, article id 084203Article in journal (Refereed) Published
##### Abstract [en]

##### Place, publisher, year, edition, pages

university of teheran, 2016
##### National Category

Physical Sciences
##### Identifiers

urn:nbn:se:kth:diva-199734 (URN)10.1103/PhysRevFluids.1.084203 (DOI)000390346800002 ()2-s2.0-85030559864 (Scopus ID)
#####

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##### Note

KTH, School of Engineering Sciences (SCI), Mechanics.

KTH, School of Engineering Sciences (SCI), Mechanics.

We analyze the angular velocity of a small neutrally buoyant spheroid log rolling in a simple shear. When the effect of fluid inertia is negligible the angular velocity. equals half the fluid vorticity. We compute by singular perturbation theory how weak fluid inertia reduces the angular velocity in an unbounded shear, and how this reduction depends upon the shape of the spheroid (on its aspect ratio). In addition we determine the angular velocity by direct numerical simulations. The results are in excellent agreement with the theory at small but not too small values of the shear Reynolds number Res, for all aspect ratios considered. For the special case of a sphere we find omega/s = -1/2 + 0.0540 Re-s(3/2) where s is the shear rate. The O( Re-s(3/2)) correction differs from that derived by Lin et al. who obtained a numerical coefficient roughly three times larger.

QC 20180214

Available from: 2017-01-25 Created: 2017-01-16 Last updated: 2018-02-14Bibliographically approvedOpen this publication in new window or tab >>Quantitative analysis of the angular dynamics of a single spheroid in simple shear flow at moderate Reynolds numbers### Rosén, Tomas

### Nordmark, Arne

### Aidun, Cyrus K.

### Do-Quang, Minh

PrimeFaces.cw("AccordionPanel","widget_formSmash_j_idt184_3_j_idt188_some",{id:"formSmash:j_idt184:3:j_idt188:some",widgetVar:"widget_formSmash_j_idt184_3_j_idt188_some",multiple:true}); ### Lundell, Fredrik

PrimeFaces.cw("AccordionPanel","widget_formSmash_j_idt184_3_j_idt188_otherAuthors",{id:"formSmash:j_idt184:3:j_idt188:otherAuthors",widgetVar:"widget_formSmash_j_idt184_3_j_idt188_otherAuthors",multiple:true}); Show others...PrimeFaces.cw("SelectBooleanButton","widget_formSmash_j_idt184_3_j_idt188_j_idt202",{id:"formSmash:j_idt184:3:j_idt188:j_idt202",widgetVar:"widget_formSmash_j_idt184_3_j_idt188_j_idt202",onLabel:"Hide others...",offLabel:"Show others..."}); 2016 (English)In: Physical Review Fluids, ISSN 2469-990X, Vol. 1, no 4, p. 044201-1-044201-21Article in journal (Refereed) Published
##### Abstract [en]

##### Place, publisher, year, edition, pages

American Institute of Physics (AIP), 2016
##### National Category

Fluid Mechanics and Acoustics
##### Identifiers

urn:nbn:se:kth:diva-193123 (URN)10.1103/PhysRevFluids.1.044201 (DOI)000390209000004 ()
#####

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##### Note

KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center. KTH, School of Engineering Sciences (SCI), Mechanics. KTH Royal Institute of Technology.

KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.

KTH, School of Engineering Sciences (SCI), Mechanics, Physicochemical Fluid Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.

KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center. KTH, School of Engineering Sciences (SCI), Mechanics.

A spheroidal particle in simple shear flow shows surprisingly complicated angular dynamics; caused by effects of fluid inertia (characterized by the particle Reynolds number *Re _{p}*) and particle inertia (characterized by the Stokes number

QC 20160929

Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2017-01-16Bibliographically approvedOpen this publication in new window or tab >>Effect of fluid and particle inertia on the rotation of an oblate spheroidal particle suspended in linear shear flow### Rosén, Tomas

### Do-Quang, Minh

### Aidun, C. K.

### Lundell, Fred

PrimeFaces.cw("AccordionPanel","widget_formSmash_j_idt184_4_j_idt188_some",{id:"formSmash:j_idt184:4:j_idt188:some",widgetVar:"widget_formSmash_j_idt184_4_j_idt188_some",multiple:true}); PrimeFaces.cw("AccordionPanel","widget_formSmash_j_idt184_4_j_idt188_otherAuthors",{id:"formSmash:j_idt184:4:j_idt188:otherAuthors",widgetVar:"widget_formSmash_j_idt184_4_j_idt188_otherAuthors",multiple:true}); 2015 (English)In: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics, ISSN 1539-3755, E-ISSN 1550-2376, Vol. 91, no 5, article id 053017Article in journal (Refereed) Published
##### Abstract [en]

##### Keywords

Lattice-Boltzmann Method, Ellipsoidal Particles, Molecular Dimensions, Viscous-Fluid, Couette Flows, Suspensions, Motion, Dynamics
##### National Category

Physical Sciences
##### Identifiers

urn:nbn:se:kth:diva-143776 (URN)10.1103/PhysRevE.91.053017 (DOI)000354927700010 ()2-s2.0-84930668697 (Scopus ID)
#####

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##### Funder

ÅForsk (Ångpanneföreningen's Foundation for Research and Development)
##### Note

KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.

KTH, School of Engineering Sciences (SCI), Mechanics, Physicochemical Fluid Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.

KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.

This work describes the inertial effects on the rotational behavior of an oblate spheroidal particle confined between two parallel opposite moving walls, which generate a linear shear flow. Numerical results are obtained using the lattice Boltzmann method with an external boundary force. The rotation of the particle depends on the particle Reynolds number, Rep = Gd-2 nu(-1) (G is the shear rate, d is the particle diameter,. is the kinematic viscosity), and the Stokes number, St = alpha Re-p (a is the solid-to-fluid density ratio), which are dimensionless quantities connected to fluid and particle inertia, respectively. The results show that two inertial effects give rise to different stable rotational states. For a neutrally buoyant particle (St = Re-p) at low Re-p, particle inertia was found to dominate, eventually leading to a rotation about the particle's symmetry axis. The symmetry axis is in this case parallel to the vorticity direction; a rotational state called log-rolling. At high Re-p, fluid inertia will dominate and the particle will remain in a steady state, where the particle symmetry axis is perpendicular to the vorticity direction and has a constant angle phi(c) to the flow direction. The sequence of transitions between these dynamical states were found to be dependent on density ratio alpha, particle aspect ratio r(p), and domain size. More specifically, the present study reveals that an inclined rolling state (particle rotates around its symmetry axis, which is not aligned in the vorticity direction) appears through a pitchfork bifurcation due to the influence of periodic boundary conditions when simulated in a small domain. Furthermore, it is also found that a tumbling motion, where the particle symmetry axis rotates in the flow-gradient plane, can be a stable motion for particles with high r(p) and low alpha.

QC 20150616. Updated from manuscript to article in journal.

Available from: 2014-03-28 Created: 2014-03-28 Last updated: 2017-12-05Bibliographically approvedOpen this publication in new window or tab >>Numerical analysis of the angular motion of a neutrally buoyant spheroid in shear flow at small Reynolds numbers### Rosen, Tomas

### Einarsson, J.

### Nordmark, Arne

### Aidun, C. K.

PrimeFaces.cw("AccordionPanel","widget_formSmash_j_idt184_5_j_idt188_some",{id:"formSmash:j_idt184:5:j_idt188:some",widgetVar:"widget_formSmash_j_idt184_5_j_idt188_some",multiple:true}); ### Lundell, Fredrik

### Mehlig, B.

PrimeFaces.cw("AccordionPanel","widget_formSmash_j_idt184_5_j_idt188_otherAuthors",{id:"formSmash:j_idt184:5:j_idt188:otherAuthors",widgetVar:"widget_formSmash_j_idt184_5_j_idt188_otherAuthors",multiple:true}); Show others...PrimeFaces.cw("SelectBooleanButton","widget_formSmash_j_idt184_5_j_idt188_j_idt202",{id:"formSmash:j_idt184:5:j_idt188:j_idt202",widgetVar:"widget_formSmash_j_idt184_5_j_idt188_j_idt202",onLabel:"Hide others...",offLabel:"Show others..."}); 2015 (English)In: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics, ISSN 1539-3755, E-ISSN 1550-2376, Vol. 92, no 6, article id 063022Article in journal (Refereed) Published
##### Abstract [en]

##### Place, publisher, year, edition, pages

American Physical Society, 2015
##### Keywords

ELLIPSOIDAL PARTICLES, FLUID INERTIA, COUETTE FLOWS, DYNAMICS, TURBULENCE, ROTATION, ORIENTATION, FORCE
##### National Category

Fluid Mechanics and Acoustics
##### Identifiers

urn:nbn:se:kth:diva-180597 (URN)10.1103/PhysRevE.92.063022 (DOI)000367081600010 ()2-s2.0-84954503118 (Scopus ID)
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##### Note

KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics.

KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.

KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.

We numerically analyze the rotation of a neutrally buoyant spheroid in a shear flow at small shear Reynolds number. Using direct numerical stability analysis of the coupled nonlinear particle-flow problem, we compute the linear stability of the log-rolling orbit at small shear Reynolds number Re-a. As Re-a -> 0 and as the box size of the system tends to infinity, we find good agreement between the numerical results and earlier analytical predictions valid to linear order in Re-a for the case of an unbounded shear. The numerical stability analysis indicates that there are substantial finite-size corrections to the analytical results obtained for the unbounded system. We also compare the analytical results to results of lattice Boltzmann simulations to analyze the stability of the tumbling orbit at shear Reynolds numbers of order unity. Theory for an unbounded system at infinitesimal shear Reynolds number predicts a bifurcation of the tumbling orbit at aspect ratio lambda(c) approximate to 0.137 below which tumbling is stable (as well as log rolling). The simulation results show a bifurcation line in the lambda-Re-a plane that reaches lambda approximate to 0.1275 at the smallest shear Reynolds number (Re-a = 1) at which we could simulate with the lattice Boltzmann code, in qualitative agreement with the analytical results.

QC 20160120

Available from: 2016-01-20 Created: 2016-01-19 Last updated: 2017-11-30Bibliographically approvedOpen this publication in new window or tab >>The dynamical states of a prolate spheroidal particle suspended in shear flow as a consequence of particle and fluid inertia### Rosén, Tomas

KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.### Do-Quang, Minh

KTH, School of Engineering Sciences (SCI), Mechanics, Physicochemical Fluid Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.### Aidun, C. K.

### Lundell, Fred

KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.PrimeFaces.cw("AccordionPanel","widget_formSmash_j_idt184_6_j_idt188_some",{id:"formSmash:j_idt184:6:j_idt188:some",widgetVar:"widget_formSmash_j_idt184_6_j_idt188_some",multiple:true}); PrimeFaces.cw("AccordionPanel","widget_formSmash_j_idt184_6_j_idt188_otherAuthors",{id:"formSmash:j_idt184:6:j_idt188:otherAuthors",widgetVar:"widget_formSmash_j_idt184_6_j_idt188_otherAuthors",multiple:true}); 2015 (English)In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 771, p. 115-158Article in journal (Refereed) Published
##### Abstract [en]

##### Keywords

bifurcation, complex fluids, multiphase and particle-laden flows
##### National Category

Other Engineering and Technologies
##### Identifiers

urn:nbn:se:kth:diva-143775 (URN)10.1017/jfm.2015.127 (DOI)000355985900009 ()2-s2.0-84928476779 (Scopus ID)
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##### Funder

Knut and Alice Wallenberg FoundationÅForsk (Ångpanneföreningen's Foundation for Research and Development)
##### Note

The rotational motion of a prolate spheroidal particle suspended in shear flow is studied by a lattice Boltzmann method with external boundary forcing (LB-EBF). It has previously been shown that the case of a single neutrally buoyant particle is a surprisingly rich dynamical system that exhibits several bifurcations between rotational states due to inertial effects. It was observed that the rotational states were associated with either fluid inertia effects or particle inertia effects, which are always in competition. The effects of fluid inertia are characterized by the particle Reynolds number Rep=4Ga^{2}/ν, where G is the shear rate, a is the length of the particle major semi-axis and ν is the kinematic viscosity. Particle inertia is associated with the Stokes number St=α· Rep, where alpha is the solid-to-fluid density ratio. Previously, the neutrally buoyant case (St=Rep) was studied extensively. However, little is known about how these results are affected when St≢Rep, and how the aspect ratio rp (major axis/minor axis) influences the competition between fluid and particle inertia in the absence of gravity. This work gives a full description of how prolate spheroidal particles in the range 2≤ rp≤ 6 behave depending on the chosen St and Rep. Furthermore, consequences for the rheology of a dilute suspension containing such particles are discussed. Finally, grid resolution close to the particle is shown to affect the quantitative results considerably. It is suggested that this resolution is a major cause of quantitative discrepancies between different studies. Thus, the results of this work and previous direct numerical simulations of this problem should be regarded as qualitative descriptions of the physics involved, and more refined methods must be used to quantitatively pinpoint the transitions between rotational states.

QC 20150609. Updated from manuscript to article in journal.

Available from: 2014-03-28 Created: 2014-03-28 Last updated: 2017-12-05Bibliographically approvedOpen this publication in new window or tab >>Effect of fluid inertia on the dynamics and scaling of neutrally buoyant particles in shear flow### Rosén, Tomas

### Lundell, Fred

KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.### Aidun, C. K.

PrimeFaces.cw("AccordionPanel","widget_formSmash_j_idt184_7_j_idt188_some",{id:"formSmash:j_idt184:7:j_idt188:some",widgetVar:"widget_formSmash_j_idt184_7_j_idt188_some",multiple:true}); PrimeFaces.cw("AccordionPanel","widget_formSmash_j_idt184_7_j_idt188_otherAuthors",{id:"formSmash:j_idt184:7:j_idt188:otherAuthors",widgetVar:"widget_formSmash_j_idt184_7_j_idt188_otherAuthors",multiple:true}); 2014 (English)In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 738, p. 563-590Article in journal (Refereed) Published
##### Abstract [en]

##### Keywords

complex fluids, multiphase and particle-laden flows, nonlinear dynamical systems
##### National Category

Engineering and Technology
##### Identifiers

urn:nbn:se:kth:diva-140130 (URN)10.1017/jfm.2013.599 (DOI)000328486400024 ()2-s2.0-84910138134 (Scopus ID)
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##### Note

KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.

The basic dynamics of a prolate spheroidal particle suspended in shear flow is studied using lattice Boltzmann simulations. The spheroid motion is determined by the particle Reynolds number (Re-p) and Stokes number (St), estimating the effects of fluid and particle inertia, respectively, compared with viscous forces on the particle. The particle Reynolds number is defined by Re-p = 4Ga(2)/nu, where G is the shear rate, a is the length of the spheroid major semi-axis and nu is the kinematic viscosity. The Stokes number is defined as St = alpha . Re-p, where alpha is the solid-to-fluid density ratio. Here, a neutrally buoyant prolate spheroidal particle (St = Re-p) of aspect ratio (major axis/minor axis) r(p) = 4 is considered. The long-term rotational motion for different initial orientations and Re-p is explained by the dominant inertial effect on the particle. The transitions between rotational states are subsequently studied in detail in terms of nonlinear dynamics. Fluid inertia is seen to cause several bifurcations typical for a nonlinear system with odd symmetry around a double zero eigenvalue. Particle inertia gives rise to centrifugal forces which drives the particle to rotate with the symmetry axis in the flow-gradient plane (tumbling). At high Re-p, the motion is constrained to this planar motion regardless of initial orientation. At a certain critical Reynolds number, Re-p = Re-c, a motionless (steady) state is created through an infinite-period saddle-node bifurcation and consequently the tumbling period near the transition is scaled as vertical bar Re-p - Re-c vertical bar(-1/2). Analyses in this paper show that if a transition from tumbling to steady state occurs at Re-p = Re-c, then any parameter beta (e. g. confinement or particle spacing) that influences the value of Re-c, such that Re-p = Re-c as beta = beta(c), will lead to a period that scales as vertical bar beta - beta c vertical bar(-1/2) and is independent of particle shape or any geometric aspect ratio in the flow.

QC 20140121

Available from: 2014-01-21 Created: 2014-01-17 Last updated: 2017-12-06Bibliographically approvedOpen this publication in new window or tab >>The influence of inertia on the rotational dynamics of spheroidal particles suspended in shear flow### Rosén, Tomas

PrimeFaces.cw("AccordionPanel","widget_formSmash_j_idt184_8_j_idt188_some",{id:"formSmash:j_idt184:8:j_idt188:some",widgetVar:"widget_formSmash_j_idt184_8_j_idt188_some",multiple:true}); PrimeFaces.cw("AccordionPanel","widget_formSmash_j_idt184_8_j_idt188_otherAuthors",{id:"formSmash:j_idt184:8:j_idt188:otherAuthors",widgetVar:"widget_formSmash_j_idt184_8_j_idt188_otherAuthors",multiple:true}); 2014 (English)Licentiate thesis, comprehensive summary (Other academic)
##### Abstract [en]

##### Abstract [sv]

##### Place, publisher, year, edition, pages

Stockholm: KTH Royal Institute of Technology, 2014. p. x, 86
##### Series

TRITA-MEK, ISSN 0348-467X ; 2014:11
##### Keywords

Fluid mechanics, dispersed particle flows, inertia, non-spherical particles, non-linear dynamics
##### National Category

Fluid Mechanics and Acoustics
##### Research subject

Engineering Mechanics
##### Identifiers

urn:nbn:se:kth:diva-143663 (URN)978-91-7595-093-8 (ISBN)
##### Presentation

2014-04-24, D3, Lindstedtsvägen 5, Stockholm, 10:15 (English)
##### Opponent

### Revstedt, Johan

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##### Supervisors

### Lundell, Fredrik

### Do-Quang, Minh

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##### Note

KTH, School of Engineering Sciences (SCI), Mechanics.

Dispersed particle flows occur in many industrial, biological and geophysical applications. The knowledge of how these flow behave can for example lead to improved material processes, better predictions of vascular diseases or more accurate climate models. These particle flows have certain properties that depend on single particle motion in fluid flows and especially how they are distributed both in terms of spatial position and, if they are non-spherical, in terms of orientation. Much is already known about the motion of perfectly spherical particles. For non-spherical particles, apart from their translation, it is important to know the the rotational motion due to local velocity gradients. Such studies have usually been restricted by the assumption that particles are extremely small compared to fluid length scales. In this limit, both inertia of the particle and inertia of the fluid can be neglected for the particle motion. This thesis gives a complete picture of how a spheroidal particle (a particle described by a rotation of an ellipse around one of its principal axes) behave in a linear shear flow when including both fluid and particle inertia, using numerical simulations. It is observed that this very simple problem possess very interesting dynamical behavior with different stable rotational states appearing as a competition between the two types of inertia. The effect of particle inertia leads to a rotation where the mass of the particle is concentrated as far away from the rotational axis as possible, i.e.\ a rotation around the minor axis. Typically, the effect of fluid inertia is instead that it tries to force the particle in a rotation where the streamlines of the flow remain as straight as possible. The first effect of fluid inertia is thus the opposite of particle inertia and instead leads to a particle rotation around the major axis. Depending on rotational state, the particles also affect the apparent viscosity of the particle dispersion. The different transitions and bifurcations between rotational states are characterized in terms of non-linear dynamics, which reveal that the particle motion probably can be described by some reduced model. The results in this theses provides fundamental knowledge and is necessary to understand flows containing non-spherical particles.

Flöden med dispergerade partiklar påträffas i många industriella, biologiska och geofysiska tillämpningar. Kunskap om hur dessa flöden beter sig kan bl.a. leda till förbättrade materialprocesser, bättre förutsägelser om hjärt- och kärlsjukdomar eller mer noggranna väderprognoser. Dessa flödens egenskaper beror på hur enskilda partiklar rör sig i en fluid och speciellt hur de är fördelade både i termer av position och, om de är icke-sfäriska, i termer av orientering. Mycket är redan känt om rörelsen av perfekt sfäriska partiklar. För icke-sfäriska partiklar är det inte bara translationen som är av intresse utan det är även viktigt att veta hur partiklarna roterar till följd av lokala hastighetsgradienter. Sådana studier har tidigare varit begränsade av antagandet att partiklarna är extremt små jämfört med fluidens typiska längdskalor. I denna gräns kan både partikelns och fluidens tröghet antas försumbar. Den här avhandlingen ger en komplett bild av hur en sfäroidisk partikel (en partikel som beskrivs av en rotation av en ellips runt en av dess huvudaxlar) beter sig i ett linjärt skjuvflöde när tröghetseffekter inkluderas. Resultaten har erhållits genom numeriska simuleringar. Det visar sig att detta enkla problem är väldigt rikt på olika dynamiska beteenden med flera stabila rotationstillstånd som uppstår tilll följd av både partikel- och fluidtröghet. Inverkan av partikeltröghet leder till en rotation där massan av partikeln är koncentrerad så långt ifrån rotationsaxeln som möjligt, d.v.s. en rotation runt lillaxeln. Den typiska inverkan av fluidtröghet är istället att fluiden försöker påtvinga partikeln en rotation där strömlinjer förblir så raka som möjligt. Primärt leder detta till att partikeln istället roterar runt storaxeln. Beroende på rotationstillstånd, så har partikeln även olika inverkan på den märkbara viskositeten av partikeldispersionen. De olika övergångarna och bifurkationerna mellan rotationstillstånd är karaktäriserade i termer av icke-linjär dynamik, vilket visar på att partikelrörelserna förmodligen kan beskrivas med en reducerad modell. Resultaten i denna avhandling är därför fundamental kunskap och ett nödvändigt steg mot att förstå beteendet av flöden med dispergerade, icke-sfäriska partiklar.

Engergy Sciences, Lunds Tekniska Högskola.

KTH, School of Engineering Sciences (SCI), Mechanics.

KTH, School of Engineering Sciences (SCI), Mechanics, Physicochemical Fluid Mechanics.

QC 20140328

Available from: 2014-03-28 Created: 2014-03-26 Last updated: 2014-03-28Bibliographically approvedOpen this publication in new window or tab >>Simulation of 3D porous media flows with application to polymer electrolyte fuel cells### Prasianakis, N. I.

### Rosén, Tomas

### Kang, J.

### Eller, J.

PrimeFaces.cw("AccordionPanel","widget_formSmash_j_idt184_9_j_idt188_some",{id:"formSmash:j_idt184:9:j_idt188:some",widgetVar:"widget_formSmash_j_idt184_9_j_idt188_some",multiple:true}); ### Mantzaras, J.

### Büchi, F. N.

PrimeFaces.cw("AccordionPanel","widget_formSmash_j_idt184_9_j_idt188_otherAuthors",{id:"formSmash:j_idt184:9:j_idt188:otherAuthors",widgetVar:"widget_formSmash_j_idt184_9_j_idt188_otherAuthors",multiple:true}); Show others...PrimeFaces.cw("SelectBooleanButton","widget_formSmash_j_idt184_9_j_idt188_j_idt202",{id:"formSmash:j_idt184:9:j_idt188:j_idt202",widgetVar:"widget_formSmash_j_idt184_9_j_idt188_j_idt202",onLabel:"Hide others...",offLabel:"Show others..."}); 2013 (English)In: Communications in Computational Physics, ISSN 1815-2406, E-ISSN 1991-7120, Vol. 13, no 3, p. 851-866Article in journal (Refereed) Published
##### Abstract [en]

##### Keywords

Fluid dynamics, Fuel cells, GDLs, Lattice Boltzmann, Porous media
##### National Category

Engineering and Technology
##### Identifiers

urn:nbn:se:kth:diva-118291 (URN)10.4208/cicp.341011.310112s (DOI)000322064800019 ()2-s2.0-84866276368 (Scopus ID)
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##### Note

Combustion Research Laboratory, Paul Scherrer Institute, Villigen PSI5232, Switzerland;Electrochemistry Laboratory, Paul Scherrer Institute, Villigen PSI 5232, Switzerland.

A 3D lattice Boltzmann (LB) model with twenty-seven discrete velocities is presented and used for the simulation of three-dimensional porous media flows. Its accuracy in combination with the half-way bounce back boundary condition is assessed. Characteristic properties of the gas diffusion layers that are used in polymer electrolyte fuel cells can be determined with this model. Simulation in samples that have been obtained via X-ray tomographic microscopy, allows to estimate the values of permeability and relative effective diffusivity. Furthermore, the computational LB results are compared with the results of other numerical tools, as well as with experimental values.

QC 20130215

Available from: 2013-02-15 Created: 2013-02-14 Last updated: 2018-06-27Bibliographically approved