Numerical simulations of sheared dense granular suspensions in transition between the Newtonian and Bagnoldian regime.

Dense suspensions constituting non-colloidal particles and a viscous carrying fluid are ubiquitous in natural processes and are also encountered in industrial applications. Rheology of these dense granular suspensions is not fully comprehended and a unified theoretical framework to describe suspension flows across various flow regimes is still lacking. Recent experiments have identified that dense granular suspensions exhibit a transition in rheology from Newtonian to Bagnoldian at a Stokes number around 10 irrespective of the volume fraction of the suspension. In the present work, we perform fully coupled, grain-resolved numerical simulations of volume-imposed and pressure-imposed rheometry using the Immersed Boundary Method which allow us to determine the stress balance in the streamwise and vertical directions of the suspension. These simulations also ascertain the stress exchange between the fluid and particle phases. We explore the aforementioned transition for a wide range of Stokes numbers as the ratio of competing inertial and viscous effects. The data will also be used to evaluate the individual contribution of contact and hydrodynamic stresses to the total stress.