| Wed September 7th 2011 16:00 ZH286 | Seminar | Rheology of dense suspensions of non-Brownian particles: Three experimental studies on normal stresses François Boyer |
Details:Suspensions of solid particles dispersed in a liquid are complex fluids that have been extensively studied for over a century. The main reason for this continuous interest is their considerable relevance for a wide range of applications. The concentrated regime, where both hydrodynamic and contact interactions contribute to the suspension mechanics, is therefore of primary interest for physicists, along with engineers, biologists, and geologists. However, despite the large number of experimental, numerical, and theoretical investigations, the rheology of suspensions remains an active research field as no unifying view has been proposed yet.The presentation focusses on issues related to normal stresses in dense suspensions of non-Brownian particles. While they play an essential role in the suspension rheology, normal stresses have been much less documented and remain far from being understood. First, considering suspensions as effective media, we report on the determination of the two normal-stress differences thanks to "free-surface methods". When the two-phase nature of suspensions is then considered, normal stress is shown to be a control parameter. Using an original experimental setup analyzed within the theoretical framework that has recently led to express universal constitutive laws for dense granular flows, we provide a new perspective on dense suspension rheology. A detailed characterization of the highly concentrated regime is obtained and a rheology, that is kept consistent with both hydrodynamic and contact interactions, is proposed. Finally, the "well-known-but-still-a-matter-of-debate" particle migration is discussed as thixotropy of rotating-rod flows will be compared to numerical predictions of previously introduced models. | ||
