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SUMMARY:APS practice talks - Emily Cook (UCL) and Jonathan Watts (Universi
 ty of Cambridge)
DTSTART:20251119T130000Z
DTEND:20251119T140000Z
UID:TALK237322@talks.cam.ac.uk
CONTACT:Emma
DESCRIPTION:*Emily Cook: Pressure-driven flow of a yield-stress fluid in a
 n annular channel with internal torque*\n\nVarious industrial problems inv
 olve transport of fluids with a yield stress along annular channels driven
  by an axial pressure gradient\, where the inner cylinder can also rotate 
 to aid mobilisation of the material. This problem is considered here for t
 he case of a Bingham fluid\, which is undeformed if the applied stress lie
 s below the fluid's yield stress. Unlike for a Newtonian fluid\, where the
  steady-state velocity field is simply a composite of axial Poiseuille flo
 w and azimuthal shear flow\, the velocity components for a Bingham fluid a
 re inherently coupled by the rheological non-linearity. The resulting stea
 dy behaviour is thus rather more complex\, and can take qualitatively diff
 erent forms\, with different regions of the fluid remaining rigid and unyi
 elded. The phase space delineating different flow regimes\, and the associ
 ated behaviour of the fluxes and flow resistance\, are outlined as a funct
 ion of the applied torque and pressure drop\, channel geometry and rheolog
 ical properties. Flow stability and the possible implications for industri
 al applications are also discussed.\n\n*Jonathan Watts: Dense suspensions 
 in ducts: μ(J) beyond simple shear*\n\nAccurately capturing the rheology 
 of dense non-Brownian suspensions is a problem with widespread application
 s in biological\, geophysical and industrial settings. There has been some
  success in modelling their behaviour under steady simple shear using the 
 family of "μ(J)" models\, but the predictions of these models in inhomoge
 neous flows have been relatively unexplored. We present a model for the pr
 essure-driven flow of a suspension of dense particles down a duct oriented
  perpendicular to the direction of gravity. This problem gives rise to a r
 ange of possible flows\, ranging from percolation of fluid through a stati
 c granular packing\, to partially mobilised particulate flow in some of th
 e duct\, and finally to fully mobile suspension flow. We explore the predi
 ctions of the model\, characterise the solutions across a range of paramet
 ers\, and make comparison with experimental results. We also discuss known
  inadequacies of the μ(J) models in describing some suspension flow pheno
 mena\, in particular the observed flow of dense suspensions below their ap
 parent yield stress\, and consider the possibility of a nonlocal dense sus
 pension theory\, by analogy with existing nonlocal models for granular flo
 ws.
LOCATION:MR12
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