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Effects of the finite particle size in turbulent wall-bounded flows of dense suspensions
Delft Univ Technol, Proc & Energy Dept Multiphase Syst, Leeghwaterstr 21, NL-2621 CA Delft, Netherlands..
Univ Padua, Dept Ind Engn, Via Venezia 1, I-35131 Padua, Italy..
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
Delft Univ Technol, Proc & Energy Dept Multiphase Syst, Leeghwaterstr 21, NL-2621 CA Delft, Netherlands..
2018 (English)In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 843, p. 450-478Article in journal (Refereed) Published
Abstract [en]

We use interface-resolved numerical simulations to study finite-size effects in turbulent channel flow of neutrally buoyant spheres. Two cases with particle sizes differing by a factor of two, at the same solid volume fraction of 20% and bulk Reynolds number are considered. These are complemented with two reference single-phase flows: the unladen case, and the flow of a Newtonian fluid with the effective suspension viscosity of the same mixture in the laminar regime. As recently highlighted in Costa etal. (Phys. Rev. Lett., vol.117, 2016, 134501), a particle-wall layer is responsible for deviations of the mesoscale-averaged statistics from what is observed in the continuum limit where the suspension is modelled as a Newtonian fluid with (higher) effective viscosity. Here we investigate in detail the fluid and particle dynamics inside this layer and in the bulk. In the particle-wall layer, the near-wall inhomogeneity has an influence on the suspension microstructure over a distance proportional to the particle size. In this layer, particles have a significant (apparent) slip velocity that is reflected in the distribution of wall shear stresses. This is characterized by extreme events (both much higher and much lower than the mean). Based on these observations we provide a scaling for the particle-to-fluid apparent slip velocity as a function of the flow parameters. We also extend the scaling laws in Costa etal. (Phys. Rev. Lett., vol.117, 2016, 134501) to second-order Eulerian statistics in the homogeneous suspension region away from the wall. The results show that finite-size effects in the bulk of the channel become important for larger particles, while negligible for lower-order statistics and smaller particles. Finally, we study the particle dynamics along the wall-normal direction. Our results suggest that single-point dispersion is dominated by particle-turbulence (and not particle-particle) interactions, while differences in two-point dispersion and collisional dynamics are consistent with a picture of shear-driven interactions.

Place, publisher, year, edition, pages
CAMBRIDGE UNIV PRESS , 2018. Vol. 843, p. 450-478
Keywords [en]
multiphase and particle-laden flows, particle/fluid flows suspensions, turbulent flows
National Category
Mechanical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-225710DOI: 10.1017/jfm.2018.117ISI: 000428165000001Scopus ID: 2-s2.0-85044259159OAI: oai:DiVA.org:kth-225710DiVA, id: diva2:1196742
Funder
Swedish Research Council
Note

QC 20180411

Available from: 2018-04-11 Created: 2018-04-11 Last updated: 2018-04-11Bibliographically approved

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Brandt, L.uca

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