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Drag reduction in turbulent channel flow laden with finite-size oblate spheroids
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
University of Padova, Department of Industrial Engineering.
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2017 (English)In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 816, p. 43-70Article in journal (Refereed) Published
Abstract [en]

We study suspensions of oblate rigid particles in a viscous fluid for different values of the particle volume fractions.Direct numerical simulations have been performed using a direct-forcing immersed boundary method to account for the dispersed phase, combined with a soft-sphere collision model and lubrication corrections for short-range particle-particle and particle-wall interactions. With respect to the single phase flow, we show that in flows laden with oblate spheroids the drag is reduced and the turbulent fluctuations attenuated.In particular, the turbulence activity decreases to lower values than those obtained by only accounting for the effective suspension viscosity.To explain the observed drag reduction we consider the particle dynamics and the interactions of the particles with the turbulent velocity field and show that the particle wall layer, previously observed and found to be responsible for the increased dissipation in suspensions of spheres, disappears in the case of oblate particles.These rotate significantly slower than spheres near the wall and tend to stay with their major axes parallel to the wall, which leads to a decrease of the Reynolds stresses and turbulence production and so to the overall drag reduction.

Place, publisher, year, edition, pages
2017. Vol. 816, p. 43-70
National Category
Fluid Mechanics and Acoustics
Identifiers
URN: urn:nbn:se:kth:diva-204160Scopus ID: 2-s2.0-85014045322OAI: oai:DiVA.org:kth-204160DiVA, id: diva2:1084195
Note

QC 20170328

Available from: 2017-03-23 Created: 2017-03-23 Last updated: 2018-12-12Bibliographically 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)
Opponent
Supervisors
Note

QC 20170328

Available from: 2017-03-28 Created: 2017-03-24 Last updated: 2017-03-28Bibliographically approved
2. Numerical study of transport phenomena in particle suspensions
Open this publication in new window or tab >>Numerical study of transport phenomena in particle suspensions
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Suspensions of solid particles in a viscous liquid are of scientific and technological interest in a wide range of applications. Sediment transport in estuaries, blood flow in the human body, pyroclastic flows from volcanos and pulp fibers in papermaking are among the examples. Often, these particulate flows also include heat transfer among the two phases or the fluid might exhibit a viscoelastic behavior. Predicting these flows and the heat transfer within requires a vast knowledge of how particles are distributed across the domain, how particles affect the flow field and finally how they affect the global behavior of the suspension. The aim of this work is therefore to improve the physical understanding of these flows, including the effect of physical and mechanical properties of the particles and the domain that bounds them.To this purpose, particle-resolved direct numerical simulations (PR-DNS) of spherical/non-spherical particles in different flow regimes and geometries are performed, using an efficient/accurate numerical tool that is developed within this work. The code is based on the Immersed Boundary Method (IBM) for the fluid-solid interactions with lubrication, friction and collision models for the close range particle-particle (particle-wall) interactions, also able to resolve for heat transfer equation in both Newtonian and non-Newtonian fluids.

Several conclusions are drawn from this study, revealing the importance of the particle's shape and inertia on the global behavior of a suspension, e.g. spheroidal particles tend to cluster while sedimenting. This phenomenon is observed here for both particles with high inertia, sedimenting in a quiescent fluid and inertialess particles (point-like tracer prolates) settling in homogeneous isotropic turbulence. The mechanisms for clustering is indeed different between these two situations, however, it is the shape of the 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 disk-like spheroidal particles. Again this drag reduction is absent for spherical particles, which instead increase the drag with respect to single-phase turbulence. In particular, we show that inertia at the particle scale induces a non-linear increase of the heat transfer as a function of the volume fraction, unlike the case at vanishing inertia where heat transfer increases linearly within the suspension.

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2019. p. 63
Series
TRITA-MEK, ISSN 0348-467X ; 2019:03
National Category
Fluid Mechanics and Acoustics
Research subject
Engineering Mechanics
Identifiers
urn:nbn:se:kth:diva-240126 (URN)978-91-7873-065-0 (ISBN)
Public defence
2019-01-25, H1, Teknikringen 33, våningsplan 5, H-huset, KTH Campus, Stockholm, 10:30 (English)
Opponent
Supervisors
Funder
EU, European Research Council, ERC-2013-CoG-616186, TRITOS
Available from: 2018-12-13 Created: 2018-12-12 Last updated: 2018-12-13Bibliographically approved

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