The role of microstructure in the rheology of sheared dense frictionless non-Brownian suspensions

We use Discrete Element Simulations (DEM) to characterize the shear rheology of frictionless non-Brownian suspensions close to jamming. The particles experience a short-range soft repulsive force sufficient to prevent frictional contacts at all the volume fractions and shear rates studied. Sheared frictionless dense suspensions exhibit a transition with increasing shear rate, from a regime of constant viscosity to one where the viscosity increases linearly with the strain-rate owing to the increased role of particle inertia. The drastic variation of transition shear-rates reported in literature necessitates a better understanding of the suspension microstructure. Our simulations show that the rheology of a suspension converges above a critical system size that is dependent on the shear rate. The viscosity in smaller systems has a dependence on the system size that increases with increasing shear rate. We find stresses due to contact forces to be higher than stresses due to hydrodynamic lubrication forces. Hence, we attribute the critical system size to the length scale associated with the formation of contacting particle clusters. This work explores the role of these particle clusters within the microstructure in influencing the suspension rheology.