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The effect of particle density in turbulent channel flow laden with finite size particles in semi-dilute conditions
KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Centra, SeRC - Swedish e-Science Research Centre.
KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Centra, SeRC - Swedish e-Science Research Centre.ORCID-id: 0000-0002-4346-4732
2016 (Engelska)Ingår i: Physics of fluids, ISSN 1070-6631, E-ISSN 1089-7666, Vol. 28, nr 3, artikel-id 033301Artikel i tidskrift (Refereegranskat) Published
Resurstyp
Text
Abstract [en]

We study the effect of varying the mass and volume fraction of a suspension of rigid spheres dispersed in a turbulent channel flow. We performed several direct numerical simulations using an immersed boundary method for finite-size particles changing the solid to fluid density ratio R, the mass fraction χ, and the volume fraction φ. We find that varying the density ratio R between 1 and 10 at constant volume fraction does not alter the flow statistics as much as when varying the volume fraction φ at constant R and at constant mass fraction. Interestingly, the increase in overall drag found when varying the volume fraction is considerably higher than that obtained for increasing density ratios at same volume fraction. The main effect at density ratios R of the order of 10 is a strong shear-induced migration towards the centerline of the channel. When the density ratio R is further increased up to 1000, the particle dynamics decouple from that of the fluid. The solid phase behaves as a dense gas and the fluid and solid phase statistics drastically change. In this regime, the collision rate is high and dominated by the normal relative velocity among particles.

Ort, förlag, år, upplaga, sidor
American Institute of Physics (AIP), 2016. Vol. 28, nr 3, artikel-id 033301
Nyckelord [en]
Low-Reynolds-Number, Numerical-Simulation, Molecular Dimensions, Suspensions, Rheology, Spheres, Fluid, Microstructure, Statistics, Stress
Nationell ämneskategori
Annan fysik
Identifikatorer
URN: urn:nbn:se:kth:diva-187293DOI: 10.1063/1.4942518ISI: 000373600600023Scopus ID: 2-s2.0-84959563104OAI: oai:DiVA.org:kth-187293DiVA, id: diva2:929853
Forskningsfinansiär
EU, Europeiska forskningsrådet, ERC-2013-CoG-616186Vetenskapsrådet
Anmärkning

QC 20160520

Tillgänglig från: 2016-05-20 Skapad: 2016-05-19 Senast uppdaterad: 2017-11-30Bibliografiskt granskad
Ingår i avhandling
1. Suspensions of finite-size rigid particles in laminar and turbulent flows
Öppna denna publikation i ny flik eller fönster >>Suspensions of finite-size rigid particles in laminar and turbulent flows
2017 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
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.

Ort, förlag, år, upplaga, sidor
Kungliga Tekniska högskolan, 2017
Serie
TRITA-MEK, ISSN 0348-467X
Nyckelord
Suspensions, complex fluids, sedimentation, rheology, turbulence
Nationell ämneskategori
Strömningsmekanik och akustik
Identifikatorer
urn:nbn:se:kth:diva-217812 (URN)978-91-7729-607-2 (ISBN)
Disputation
2017-12-15, D3, Lindstedtsvägen 5, Stockholm, 10:15 (Engelska)
Opponent
Handledare
Forskningsfinansiär
EU, Europeiska forskningsrådet, ERC-2013-CoG-616186, TRITOS
Anmärkning

QC 20171117

Tillgänglig från: 2017-11-17 Skapad: 2017-11-16 Senast uppdaterad: 2017-11-29Bibliografiskt granskad

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Brandt, Luca

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Fornari, WalterBrandt, Luca
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MekanikLinné Flow Center, FLOWSeRC - Swedish e-Science Research Centre
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Physics of fluids
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