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Angular dynamics of non-spherical particles in linear flows related to production of biobased materials
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.ORCID iD: 0000-0002-2346-7063
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

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.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2016. , 134 p.
Series
TRITA-MEK, ISSN 0348-467X ; 2016:14
Keyword [en]
Fluid mechanics, dispersed particle flows, inertia, non-linear dynamics, rotary diffusion, characterization techniques
National Category
Fluid Mechanics and Acoustics
Identifiers
URN: urn:nbn:se:kth:diva-193124ISBN: 978-91-7729-139-8 (print)OAI: oai:DiVA.org:kth-193124DiVA: diva2:981176
Public defence
2016-10-28, F2, Lindstedsvägen 26, Stockholm, 10:30 (English)
Opponent
Supervisors
Note

QC 20160929

Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2016-09-29Bibliographically approved
List of papers
1. Effect of fluid inertia on the dynamics and scaling of neutrally buoyant particles in shear flow
Open this publication in new window or tab >>Effect of fluid inertia on the dynamics and scaling of neutrally buoyant particles in shear flow
2014 (English)In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 738, 563-590 p.Article in journal (Refereed) Published
Abstract [en]

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.

Keyword
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)
Note

QC 20140121

Available from: 2014-01-21 Created: 2014-01-17 Last updated: 2017-12-06Bibliographically approved
2. The dynamical states of a prolate spheroidal particle suspended in shear flow as a consequence of particle and fluid inertia
Open 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
2015 (English)In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 771, 115-158 p.Article in journal (Refereed) Published
Abstract [en]

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=4Ga2/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.

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

QC 20150609. Updated from manuscript to article in journal.

Available from: 2014-03-28 Created: 2014-03-28 Last updated: 2017-12-05Bibliographically approved
3. Effect of fluid and particle inertia on the rotation of an oblate spheroidal particle suspended in linear shear flow
Open 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
2015 (English)In: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics, ISSN 1539-3755, E-ISSN 1550-2376, Vol. 91, no 5, 053017Article in journal (Refereed) Published
Abstract [en]

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.

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

QC 20150616. Updated from manuscript to article in journal.

Available from: 2014-03-28 Created: 2014-03-28 Last updated: 2017-12-05Bibliographically approved
4. Numerical analysis of the angular motion of a neutrally buoyant spheroid in shear flow at small Reynolds numbers
Open 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
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, 063022Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
American Physical Society, 2015
Keyword
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)
Note

QC 20160120

Available from: 2016-01-20 Created: 2016-01-19 Last updated: 2017-11-30Bibliographically approved
5. Quantitative analysis of the angular dynamics of a single spheroid in simple shear flow at moderate Reynolds numbers
Open 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
Show others...
2016 (English)In: Physical Review Fluids, ISSN 2469-990X, Vol. 1, no 4, 044201-1-044201-21 p.Article in journal (Refereed) Published
Abstract [en]

A spheroidal particle in simple shear flow shows surprisingly complicated angular dynamics; caused by effects of fluid inertia (characterized by the particle Reynolds number Rep) and particle inertia (characterized by the Stokes number St). Understanding this behavior can provide important fundamental knowledge of suspension flows with spheroidal particles. Up to now only qualitative analysis has been available at moderate Rep. Rigorous analytical methods apply only to very small Rep and numerical results lack accuracy due to the difficulty in treating the moving boundary of the particle. Here we show that the dynamics of the rotational motion of a prolate spheroidal particle in a linear shear flow can be quantitatively analyzed through the eigenvalues of the log-rolling particle (particle aligned with vorticity). This analysis provides an accurate description of stable rotational states in terms of Rep,St, and particle aspect ratio (rp). Furthermore we find that the effect on the orientational dynamics from fluid inertia can be modeled with a Duffing-Van der Pol oscillator. This opens up the possibility of developing a reduced-order model that takes into account effects from both fluid and particle inertia.

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 ()
Note

QC 20160929

Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2017-01-16Bibliographically approved
6. Chaotic rotation of a spheroidal particle in simple shear flow
Open this publication in new window or tab >>Chaotic rotation of a spheroidal particle in simple shear flow
(English)Manuscript (preprint) (Other academic)
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-193117 (URN)
Note

QC 20160930

Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2016-09-30Bibliographically approved
7. Orientational dynamics of a tri-axial ellipsoid in simple shear flow: influence of inertia
Open this publication in new window or tab >>Orientational dynamics of a tri-axial ellipsoid in simple shear flow: influence of inertia
Show others...
(English)Manuscript (preprint) (Other academic)
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-193119 (URN)
Note

QC 20160930

Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2016-09-30Bibliographically approved
8. Evaluating alignment of elongated particles in cylindrical flows through small angle scattering experiments
Open this publication in new window or tab >>Evaluating alignment of elongated particles in cylindrical flows through small angle scattering experiments
(English)Manuscript (preprint) (Other academic)
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-193120 (URN)
Note

QC 20160929

Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2016-09-29Bibliographically approved
9. Measuring rotary diffusion of dispersed cellulose nanofibrils using Polarized Optical Microscopy
Open this publication in new window or tab >>Measuring rotary diffusion of dispersed cellulose nanofibrils using Polarized Optical Microscopy
Show others...
(English)Manuscript (preprint) (Other academic)
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-193121 (URN)
Note

QC 20160929

Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2016-09-29Bibliographically approved
10. On the applicability of time-resolved synchrotron X-ray techniques for studying rotary diffusion of dispersed cellulose nanofibrils
Open this publication in new window or tab >>On the applicability of time-resolved synchrotron X-ray techniques for studying rotary diffusion of dispersed cellulose nanofibrils
Show others...
(English)Manuscript (preprint) (Other academic)
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-193122 (URN)
Note

QC 20160929

Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2016-09-29Bibliographically approved

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