Some key physical ingredients in dense suspension simulations

International audienceThis numerical work intends to highlight the most prominent physical ingredients needed for reliable simulations of dense suspensions. We especially address the role of friction, roughness, and long-range hydrodynamics. Simulations show that friction between particles significantly alters viscosity and normal stresses and leads to an improved correlation with available experiments. A new finding is that friction also increases particle diffusion by a factor of two and provides better agreement on the irreversibility threshold in Pine's experiments. Particle roughness is numerically shown to alter rheology only slightly : a large roughness leads to a small decrease in the viscosity since lubrication dissipation is lowered. Frictional roughness seems to minimize this even more and, by and large, roughness size has only limited effects on rheology. However, large roughness and confinement can trigger the onset of particle layering which strongly decreases diffusion. Finally, we have evaluated the effect of long-range hydrodynamics in dense suspensions. To this end, we have compared full Stokes simulations with widely used molecular dynamics simulations. Our first results on frictionless particles show that there is a slight difference on viscosity although it still diverges similarly (same φ* ≈ 0.64 and similar critical exponent) whether long-range interactions are accounted or not. Frictional simulations are on the way to confirm this behavior