Numerical simulations of dense granular suspensions in laminar flow under constant and varying shear rates

Using an immersed boundary-lattice Boltzmann method, we investigated the response of dense granular suspensions to time-varying shear rates and flow reversals. The evolution of the relative apparent viscosity and particle structures was analysed. The concentration of solids (𝜙𝑣) and particle Reynolds numbers (𝑅𝑒𝑝) were varied over the ranges 6% ≤ 𝜙𝑣 ≤ 47% and 0.105 ≤ 𝑅𝑒𝑝 ≤ 0.529. The simulations included sub-grid scale corrections for unresolved lubrication forces and torques (normal and tangential). When 𝜙𝑣 surpasses 30%, the contribution of the tangential lubrication corrections to the shear stress is dominant. While for intermediate solids fractions we find weak shear-thinning, we see weak shear-thickening for 𝜙𝑣 > 40%. We show how the structure and apparent viscosity of a suspension evolves after a reversal of the shear direction. For 47% solids, simulations with step changes in the shear rate show the effects of the previous shear history on the viscosity of the suspension.