Fluid mechanics and rheology of dense suspensions

We review the fluid mechanics and rheology of dense suspensions, emphasizing investigations of microstructure and total stress. "Dense" or "highly concentrated" suspensions are those in which the average particle separation distance is less than the particle radius. For these suspensions, multiple-body interactions as well as two-body lubrication play a significant role and the rheology is non-Newtonian. We include investigations of multimodal suspensions, but not those of suspensions with dominant nonhydrodynamic interactions. We consider results from both physical experiments and computer simulations and explore scaling theories and the development of constitutive equations.