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Dense suspension rheology, normal stresses, and migration
Dense or highly concentrated particulate systems are very common in several engineering fields such as civil engineering, food or pharmaceutical industry as well as in geophysical situations such as debris flows, sediment transport, and submarine avalanches.
The fundamental problem is to determine the response of these systems to imposed forces and motions at their boundary, i.e. to determine their rheological properties from a knowledge of the mechanics of the particles and the interstitial fluid. The major difficulty is that the grains interact both by hydrodynamic interactions through the liquid and by mechanical contact.
In this talk, we will first provide a simple review of dense suspension rheology and show that it exhibits a number of non-Newtonian behaviors. We will then focus on the occurrence of normal stress differences in these systems and present two new experimental determinations of these differences using rotating-rod rheometry and tilted-trough flow. Suspension of spherical particles but also of elongated rod-like particles will be examined. We will finally discuss particle migration from regions of high to low shear-rate which can occur in different flow geometries such as large-gap Couette or pipe flows.
This work has been done in collaboration with J.E. Butler, F. Boyer, E. Couturier, L. M. Davidson, O. Pouliquen, and B. Snook.