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Inertial migration of spherical and oblate particles in straight ducts
KTH, School of Engineering Sciences (SCI), Mechanics.ORCID iD: 0000-0002-0122-401X
KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.ORCID iD: 0000-0003-4328-7921
KTH, School of Biotechnology (BIO), Proteomics and Nanobiotechnology.
KTH, School of Biotechnology (BIO), Proteomics and Nanobiotechnology.
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(English)In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645Article in journal (Refereed) Accepted
Abstract [en]

We study numerically the inertial migration of a single rigid sphere and an oblate spheroid in straight square and rectangular ducts. A highly accurate interface-resolved numerical algorithm is employed to analyse the entire migration dynamics of the oblate particle and compare it with that of the sphere. Similarly to the inertial focusing of spheres, the oblate particle reaches one of the four face-centred equilibrium positions, however they are vertically aligned with the axis of symmetry in the spanwise direction. In addition, the lateral trajectories of spheres and oblates collapse into an equilibrium manifold before ending at the equilibrium positions, with the equilibrium manifold tangential to lines of constant background shear for both sphere and oblate particles. The differences between the migration of the oblate and sphere are also presented, in particular the oblate may focus on the diagonal symmetry line of the duct cross-section, close to one of the corners, if its diameter is larger than a certain threshold. Moreover, we show that the final orientation and rotation of the oblate exhibit a chaotic behaviour for Reynolds numbers beyond a critical value. Finally, we document that the lateral motion of the oblate particle is less uniform than that of the spherical particle due to its evident tumbling motion throughout the migration. In a square duct, the strong tumbling motion of the oblate in the first stage of the migration results in a lower lateral velocity and consequently longer focusing length with respect to that of the spherical particle. The opposite is true in a rectangular duct where the higher lateral velocity of the oblate in the second stage of the migration, with negligible tumbling, gives rise to shorter focusing lengths.These results can help the design of microfluidic systems for bio-applications.

National Category
Fluid Mechanics and Acoustics
Identifiers
URN: urn:nbn:se:kth:diva-204162DOI: 10.1017/jfm.2017.189ISI: 000405373500005Scopus ID: 2-s2.0-85018317724OAI: oai:DiVA.org:kth-204162DiVA, id: diva2:1084197
Note

QC 20170328

Available from: 2017-03-23 Created: 2017-03-23 Last updated: 2017-08-03Bibliographically approved
In thesis
1. Numerical study of non-spherical/spherical particles in laminar and turbulent flows
Open this publication in new window or tab >>Numerical study of non-spherical/spherical particles in laminar and turbulent flows
2017 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The presence of solid rigid particles alters the global transport and rheological properties of the mixture in complex (and often unpredictable) ways. In recent years a few studies have been devoted to investigating the behavior of dense suspensions in the turbulent/inertial regime with the majority of theses analyses limited to mono-disperse rigid neutrally-buoyant spheres. However, one interesting parameter that is rarely studied for particles with high inertia is the particle shape. Spheroidal particles introduce an anisotropy, e.g. a tendency to orient in a certain direction, which can affect the bulk behavior of a suspension in an unexpected ways. The main focus of this study is therefore to investigate the behavior of spheroidal particles and their effect on turbulent/inertial flows.

We perform fully resolved simulations of particulate flows with spherical/spheroidal particles, using an efficient/accurate numerical approach that enables us to simulate thousands of particles with high resolutions in order to capture all the fluid-solid interactions.

Several conclusions are drawn from this study that reveal the importance of particle's shape effect on the behaviour of a suspension e.g. spheroidal particles tend to cluster while sedimenting. This phenomenon is observed in this work for both particles with high inertia, sedimenting in a quiescent fluid and inertialess particles (point-like tracer prolates) settling in homogenous isotropic turbulence. The mechanisms for clustering is indeed different between these two situations, however, it is the shape of particles that governs these mechanisms, as clustering is not observed for spherical particles. Another striking finding of this work is drag reduction in particulate turbulent channel flow with rigid oblate particles. Again this drag reduction is absent for spherical particles, which instead increase the drag with respect to single-phase turbulence. 

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2017. p. 31
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-204421 (URN)978-91-7729-333-0 (ISBN)
Presentation
2017-04-20, E51, Osquars backe 14, Stockholm, 14:00 (English)
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Supervisors
Note

QC 20170328

Available from: 2017-03-28 Created: 2017-03-24 Last updated: 2017-03-28Bibliographically approved

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