Simulations of the start-up of shear flow of 2D particle suspensions in viscoelastic fluids : structure formation and rheology

We present simulations of the start-up of shear flow of 2D suspensions of rigid particles in viscoelastic fluids. A novel numerical method is applied that makes use of biperiodic domains, which act as representative volume elements of the suspension. Local mesh refine- ment ensures the method is both accurate and efficient, without the need for a repulsive potential between the particles. By averaging many simulations for random initial positions of the particles, we obtain the true rheological bulk response of the material. At Weissenberg numbers of 1 and higher, particle chaining is observed that leads to a decrease in bulk viscos- ity, an effect that was observed experimentally in [1]. Increasing the solid area fraction leads to the particle alignment occuring faster and the particles forming longer chains, causing a stronger decrease in bulk viscosity. In addition, at solid area fractions of 0.3 and higher, an increase of the bulk first normal stress difference is observed, which may be attributed to an increase in local shear rate in between the particle chains. Finally, flow cessation is simulated and it is found that the particle chains are preserved until all elastic stresses in the fluid have relaxed.