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Inertial migration in dilute and semidilute suspensions of rigid particles in laminar square duct
KTH, School of Engineering Sciences (SCI), Mechanics. KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
KTH, School of Engineering Sciences (SCI), Mechanics, Physicochemical Fluid Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre.ORCID iD: 0000-0003-0418-7864
KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre.ORCID iD: 0000-0002-4346-4732
2017 (English)In: Physical Review Fluids, ISSN 1943-6947, E-ISSN 1553-0124, Vol. 2, no 8, article id 084301Article in journal (Refereed) Published
Abstract [en]

We study the inertial migration of finite-size neutrally buoyant spherical particles in dilute and semidilute suspensions in laminar square duct flow. We perform several direct numerical simulations using an immersed boundary method to investigate the effects of the bulk Reynolds number Re-b, particle Reynolds number Re-p, and duct to particle size ratio h/a at different solid volume fractions phi, from very dilute conditions to 20%. We show that the bulk Reynolds number Re-b is the key parameter in inertial migration of particles in dilute suspensions. At low solid volume fraction (phi = 0.4%), low bulk Reynolds number (Re-b = 144), and h/a = 9 particles accumulate at the center of the duct walls. As Re-b is increased, the focusing position moves progressively toward the corners of the duct. At higher volume fractions, phi = 5%, 10%, and 20%, and in wider ducts (h/a = 18) with Re-b = 550, particles are found to migrate away from the duct core toward the walls. In particular, for phi = 5% and 10%, particles accumulate preferentially at the corners. At the highest volume fraction considered, phi = 20%, particles sample all the volume of the duct, with a lower concentration at the duct core. For all cases, we find that particles reside longer times at the corners than at the wall centers. In a duct with lower duct to particle size ratio h/a = 9 (i.e., with larger particles), phi = 5%, and high bulk Reynolds number Re-b = 550, we find a particle concentration pattern similar to that in the ducts with h/a = 9 regardless of the solid volume fraction phi. Instead, for lower Bulk Reynolds number Re-b = 144, h/a = 9, and phi = 5%, a different particle distribution is observed in comparison to a dilute suspension phi = 0.4%. Hence, the volume fraction plays a key role in defining the final distribution of particles in semidilute suspensions at low bulk Reynolds number. The presence of particles induces secondary cross-stream motions in the duct cross section, for all phi. The intensity of these secondary flows depends strongly on particle rotation rate, on the maximum concentration of particles in focusing positions, and on the solid volume fraction. We find that the secondary flow intensity increases with the volume fraction up to phi = 5%. However, beyond phi = 5% excluded-volume effects lead to a strong reduction of cross-stream velocities for Re-b = 550 and h/a = 18. Inhibiting particles from rotating also results in a substantial reduction of the secondary flow intensity and in variations of the exact location of the focusing positions.

Place, publisher, year, edition, pages
American Physical Society, 2017. Vol. 2, no 8, article id 084301
National Category
Fluid Mechanics and Acoustics
Identifiers
URN: urn:nbn:se:kth:diva-217628DOI: 10.1103/PhysRevFluids.2.084301ISI: 000407101700001Scopus ID: 2-s2.0-85035330723OAI: oai:DiVA.org:kth-217628DiVA, id: diva2:1157333
Funder
Swedish e‐Science Research CenterEU, Horizon 2020, ERC-2013-CoG-616186Swedish Research Council
Note

QC 20171116

Available from: 2017-11-15 Created: 2017-11-15 Last updated: 2017-12-11Bibliographically approved
In thesis
1. Suspensions of finite-size rigid particles in laminar and turbulent flows
Open this publication in new window or tab >>Suspensions of finite-size rigid particles in laminar and turbulent flows
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Dispersed multiphase flows occur in many biological, engineering and geophysical applications. Understanding the behavior of suspensions is a difficult task. In the present work, we numerically study the behavior of suspensions of finite-size rigid particles in different flows. Firstly, the sedimentation of spherical particles larger than the Taylor microscale in sustained homogeneous isotropic turbulence and quiescent fluid is investigated. The results show that the mean settling velocity is lower in an already turbulent flow than in a quiescent fluid. We also investigate the settling in quiescent fluid of oblate particles. We find that at low volume fractions the mean settling speed of the suspension is substantially larger than the terminal speed of an isolated oblate. Suspensions of finite-size spheres are also studied in turbulent channel flow. First, we change the solid volume and mass fractions, and the solid-to-fluid density ratio in an idealized scenario where gravity is neglected. Then we investigate the effects of polydispersity. It is found that the statistics are substantially altered by changes in volume fraction. We then consider suspensions of solid spheres in turbulent duct flows. We see that particles accumulate mostly at the corners or at the core depending on the volume fraction. Secondary motions are enhanced by increasing the volume fraction, until excluded volume effects are so strong that the turbulence activity is reduced. The inertial migration of spheres in laminar square duct flows is also investigated. We consider semi-dilute suspensions at different bulk Reynolds numbers and duct-to-particle size ratios. The highest particle concentration is found around the focusing points, except at very large volume fractions. Finally we study the rheology of confined dense suspensions of spheres in simple shear flow. We focus on the weakly inertial regime and show that the effective viscosity varies non-monotonically with increasing confinement.

Place, publisher, year, edition, pages
Kungliga Tekniska högskolan, 2017
Series
TRITA-MEK, ISSN 0348-467X
Keyword
Suspensions, complex fluids, sedimentation, rheology, turbulence
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-217812 (URN)978-91-7729-607-2 (ISBN)
Public defence
2017-12-15, D3, Lindstedtsvägen 5, Stockholm, 10:15 (English)
Opponent
Supervisors
Funder
EU, European Research Council, ERC-2013-CoG-616186, TRITOS
Note

QC 20171117

Available from: 2017-11-17 Created: 2017-11-16 Last updated: 2017-11-29Bibliographically approved

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