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Effects of inertia and turbulence on rheological measurements of neutrally buoyant suspensions

Linares-Guerrero, Esperanza and Hunt, Melany L. and Zenit, Roberto (2017) Effects of inertia and turbulence on rheological measurements of neutrally buoyant suspensions. Journal of Fluid Mechanics, 811 . pp. 525-543. ISSN 0022-1120. doi:10.1017/jfm.2016.763.

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For low-Reynolds-number shear flows of neutrally buoyant suspensions, the shear stress is often modelled using an effective viscosity that depends only on the solid fraction. As the Reynolds number (Re) is increased and inertia becomes important, the effective viscosity also depends on the Reynolds number itself. The current experiments measure the torque for flows of neutrally buoyant particles in a coaxial-cylinder rheometer for solid fractions, ϕ, from 10 % to 50 % and Reynolds numbers based on particle diameter from 2 to 1000. For experiments for Reynolds of O(10) and solid fractions less than 30%, the effective viscosity increases with Reynolds number, in good agreement with recent numerical simulations found in the literature. At higher solid fractions over the same range of Re, the results show a decrease in torque with shear rate. For Reynolds numbers greater than 100 and lower solids concentrations, the effective viscosity continues to increase with Reynolds number. However, based on comparisons with pure fluid measurements the increase in the measured effective viscosity results from the transition to turbulence. The particles augment the turbulence by increasing the magnitude of the measured torques and causing the flow to transition at lower Reynolds numbers. For the highest solid fractions, the measurements show a significant increase in the magnitude of the torques, but the effective viscosity is independent of Reynolds number.

Item Type:Article
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Hunt, Melany L.0000-0001-5592-2334
Additional Information:© 2016 Cambridge University Press. Received 20 November 2015; revised 20 July 2016; accepted 9 November 2016; first published online 13 December 2016. We thank Professor C. E. Brennen for his comments and fruitful discussions. R.Z. is grateful to the Fulbright-Garcia Robles foundation and to the PASPA-DGAPA-UNAM program for their financial support during his sabbatical year at Caltech.
Funding AgencyGrant Number
Fulbright-Garcia Robles FoundationUNSPECIFIED
Universidad Nacional Autónoma de México (UNAM)UNSPECIFIED
Subject Keywords:particle/fluid flows, suspensions, transition to turbulence
Record Number:CaltechAUTHORS:20170112-110444245
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:73468
Deposited By: Tony Diaz
Deposited On:20 Jan 2017 00:12
Last Modified:11 Nov 2021 05:17

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