Direct 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 apparent viscosity and the evolution of particle
clusters were analysed. The solids fractions and particle Reynolds
numbers varied over the ranges 5% ≤ φv ≤ 47%
and 0.11 ≤ Rep ≤ 0.32. The simulations included
sub-grid scale corrections for unresolved lubrication forces. The
contribution of the tangential lubrication corrections to the shear
stress is dominant when φv surpasses 30%. For
φv > 35%, increasing
shear-thickening is seen with increasing φv.
Following a shear reversal, the number of clusters temporarily increases
and then decreases to a stable value over the same time scale as the
development of the wall shear stress (and apparent viscosity).
Simulations with several step changes in the shear rate show the effects
of the previous shear history on the viscosity of the suspension.