Direct numerical simulation of particle alignment in viscoelastic fluids

The numerical method allows for the detailed investigation of particles interacting in viscoelastic flows. Alignment of two and three particles is observed in the simulations. Morphology plots were created for various values of α, β and Wi. Alignment is mainly governed by the value of the elasticity parameter S, defined as half of the ratio between the first normal stress difference and shear stress of the suspending fluid. Alignment appears to occur above a critical value of S, which decreases with increasing α, thus shear thinning promotes alignment. Furthermore, three particles align at lower S than two particles. Finally, simulations were performed in a shear-thinning Carreau fluid, where we never observed alignment of the particles. These results lead us to the conclusion that the presence of normal stress differences is essential for particle alignment to occur, although it is strongly promoted by shear thinning.