日時
2017年12月22日(金) 10:30–
場所
大阪大学サイバーメディアセンター 7F 会議室
題目
How do dense suspensions flow? — Non-equilibrium microstructure and frictional contacts
発表者
瀬戸 亮平 氏 (OIST)
要旨

Mixtures of stiff particles and viscous liquids can be considered as incompressible fluids as long as the packing fraction is not too high. However, they flow in very different manners from usual fluids (i.e., Newtonian fluids). Rheological measurements show a peculiar shear-rate dependence of their viscosities, displaying both shear thinning and thickening including a discontinuous jump in the viscosity for sufficiently concentrated systems. Normal stress differences, which are another independent signature of non-Newtonian behavior in steady flows, are also not zero.
Such non-Newtonian nature originates from the slow dynamics of suspended particles in viscous liquids. In sheared suspensions, particle arrangements are far from relaxed or equilibrium states. Interactions among particles in such flow-induced microstructures need to be considered to evaluate their rheology. Our simulation, combining the two simulation strategies of Stokesian Dynamics and the Discrete Element Method, can capture such particle dynamics and reproduce the experimentally observed rheology of dense suspensions. The simulation results give a clear understanding of the mechanism of discontinuous shear thickening, on which researchers had not reached consensus (Seto, et. al. PRL, 111, 2013 and Mari, et. al., PNAS, 112(50), 2015).
To access a more complete set of rheological responses, we impose both simple shear and planar extensional flows by using time-dependent periodic boundary conditions: the Lees–Edwards and Kraynik–Reinelt boundary conditions, respectively. The comparison of the effects in the two flow conditions provides further insight into the role of flow-induced microstructure and possible constitutive relations for dense suspensions (Seto, et. al., JFM, 825:R3, 2017).