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International audience; We perform local measurements of both the velocity and the particle volume fraction to study viscous resuspension in non-Brownian suspensions for Shields numbers ranging from to . With this aim, a suspension of polymethacrylate spherical particles dispersed in a lighter Newtonian fluid (Triton X100) is sheared in a vertical Couette cell where both velocity and particle density mappings are performed. We show that the radial profiles of the velocity and of the particle volume fraction are inconsistent in the framework of local rheology of a Newtonian material and that these discrepancies disappear for a neutrally buoyant suspension. The vertical concentration profiles are used to deduce the third particle normal stress, Sigma(p)(33), by solving the Cauchy equation. The value of Sigma(p)(33) is shown not to vary linearly with shear rate but rather through a power law with an exponent close to 0.7, irrespective of the value of the particle volume fraction, in accordance with the recent results of Saint-Michel et al. (Phys. Fluids, vol. 31, 2019, 103301). Finally, we compare our results with the results of previous studies where alpha(3) = Sigma(p)(33)/eta 0(gamma) over dot (with eta(0) the viscosity of the suspending liquid and (gamma) over dot the shear rate) was deduced from the macroscopic measurement of the height of the resuspended layer. The agreement is satisfactory.

Shear thickening is a widespread phenomenon in suspension flow that, despite sustained study, is still the subject of much debate. The longstanding view that shear thickening is due to hydrodynamic clusters has been challenged by recent theory and simulations suggesting that contact forces dominate, not only in discontinuous, but also in continuous shear thickening. Here, we settle this dispute using shear reversal experiments on micron-sized silica and latex particles to measure directly the hydrodynamic and contact force contributions to shear thickening. We find that contact forces dominate even continuous shear thickening. Computer simulations show that these forces most likely arise from frictional interactions.

In this paper we present a novel numerical scheme for simulating the one-dimensional deformation of hydrogel material due to drying or rehydration. The scheme is based on the versatile Lattice Boltzmann method, which has been extended such that the computational grid (lattice) deforms due to shrinkage or swelling. This property of a deforming grid is new to the lattice Boltzmann method, and a detailed description of this new method is given. Via simulations we show that self-similar moisture concentration profiles occur in two periods in both drying and swelling processes: the penetration period and the regular regime. Given the property of self-similarity, we have been able to formulate a reduced-order model for the regular regime of swelling.

Shear thickening, an increase of viscosity with shear rate, is a ubiquitous phenomenon in suspended materials that has implications for broad technological applications. Controlling this thickening behavior remains a major challenge and has led to empirical strategies ranging from altering the particle surfaces and shape to modifying the solvent properties. However, none of these methods allows for tuning of flow properties during shear itself. Here, we demonstrate that by strategic imposition of a high-frequency and low-amplitude shear perturbation orthogonal to the primary shearing flow, we can largely eradicate shear thickening. The orthogonal shear effectively becomes a regulator for controlling thickening in the suspension, allowing the viscosity to be reduced by up to 2 decades on demand. In a separate setup, we show that such effects can be induced by simply agitating the sample transversely to the primary shear direction. Overall, the ability of in situ manipulation of shear thickening paves a route toward creating materials whose mechanical properties can be controlled., I.C. and N.Y.C.L. gratefully acknowledge the Weitz Laboratory at Harvard University, School of Engineering and Applied Sciences for generous use of their rheometry facility. I.C. and N.Y.C.L. were supported by National Science Foundation (NSF) CBET-PMP Award 1232666 and continued support from NSF CBET-PMP Award 1509308. C.N. and J.S. acknowledge funding from the Engineering and Physical Sciences Research Council (EPSRC), EP/N025318/1. M.E.C. is supported by the Royal Society and EPSRC Grant EP/J007404. This work also made use of the Cornell Center for Materials Research Shared Facilities, which are supported through the NSF Materials Research Science and Engineering Centers Program (DMR-1120296)., This is the author accepted manuscript. The final version is available from the National Academy of Sciences via http://dx.doi.org/10.1073/pnas.1608348113

We use shear-reversal simulations to explore the rheology of dense, non-Brownian, noninertial, suspensions, resolving lubrication forces between neighboring particles and modeling particle surface contacts. The transient stress response to an abrupt reversal of the direction of shear shows rate-independent, nonmonotonic behavior, capturing the salient features of the corresponding classical experiments. Based on analyses of the hydrodynamic and particle contact stresses and related contact networks, we demonstrate distinct responses at small and large strains, associated with contact breakage and structural reorientation, respectively, emphasizing the importance of particle contacts. Consequently, the hydrodynamic and contact stresses evolve over disparate strain scales and with opposite trends, resulting in nonmonotonic behavior when combined. We further elucidate the roles of particle roughness and repulsion in determining the microstructure and hence the stress response at each scale.

By extending the concept of an effective temperature, earlier introduced for sheared monodisperse suspensions, we propose a continuum theory for sheared bidisperse suspensions. We show the theory for sheared suspensions can be constructed from the theory for Brownian suspensions by replacing the temperature with the effective temperature. Furthermore, we explore the validity of closure relations based on mean field/free volume theory, by comparison with experimental data obtained for Brownian bidisperse suspensions. In a recent paper, we have shown that the new theory, combined with the discussed closure relations, is indeed a predictive theory.

In this paper we review simulation methods, which address suspension flows at different length scales. Taking the multiscale problem of confined suspension flow in fractionation and sorting applications as a guiding example, we discuss these numerical methods for use in a multiscale simulation framework. We have classified the methods in terms of dimensionless numbers, governing the physics of confined suspension flows, and the resolution of particles on the computation grid. From our literature review, we conclude, that for suspension flows at Peclet numbers larger than unity, Lattice Boltzmann is a good method to implement for all levels of the multiscale simulation framework.