(390c) Numerical Simulation Study of the Rheology of Suspensions of Rigid Spheres in a Viscoelastic Fluid Matrix Under Imposed Shear

The stress behavior of suspensions in viscoelastic fluids is of considerable interest because of the frequent occurrence of such materials in commercial processing operations and the design of polymeric fluids with better particle transport properties for applications such as oil recovery and microfluidics.  We present 3D simulations of neutrally buoyant rigid spheres freely suspended in a viscoelastic fluid matrix under imposed shear flow using the Giesekus constitutive model.  In the dilute particle concentration limit, we study the particle contribution to the bulk stress for Weissenburg numbers ranging from 0 to 5 and discuss the competing effects between the particle stresslet and the particle induced polymer stress in the fluid domain in determining the viscometric functions of the suspension.  At low Weissenburg number, we compare our simulation results with a few theoretical works that exist for a dilute suspension of spheres in a weakly non-Newtonian fluid matrix to elucidate the discrepancy that exists in the literature regarding the second normal stress difference and show that the volume averaged polymeric stress in the fluid domain has a nonnegligible particle contribution.  We also implement viscoelasticity in an immersed boundary framework to study particle-particle interactions.  We examine the effect of particle-particle interactions on the particle stresslet and compare simulation results with experimental measurements.