  Granular suspensions present a transition from a Newtonian rheology in the
Stokes limit to a Bagnoldian rheology when inertia is increased. A custom
rheometer which can be run in a pressure or a volume-imposed mode is used to
examine this transition in the dense regime close to jamming. By varying
systematically the interstitial fluid, shear rate, and packing fraction in
volume-imposed measurements, we show that the transition takes place at a
Stokes number of 10 independent of the packing fraction. Using pressure-imposed
rheometry, we investigate whether the inertial and viscous regimes can be
unified as a function of a single dimensionless number based on stress
additivity.
