Pairwise interaction of capsules in simple shear flow:: Three-dimensional effects

We use a boundary integral formulation to investigate the collision of two identical capsules in simple shear flow. Each capsule consists of a viscous liquid drop enclosed by an elastic membrane. The hydrodynamic interaction is characterized by an irreversible cross-flow displacement after the capsules have crossed each other, as also observed for rough spheres or drops. This deflection would cause a shear-induced dispersion in a dilute suspension of capsules. After a previous work devoted to the interaction of two capsules located in the same shear plane, here, we focus on the more general case of capsules also shifted in the vorticity direction. For sufficiently spaced trajectories, the capsules exhibit negative deflections which displace them to closer streamlines after they have crossed. Furthermore, the cross-flow displacement occurs mainly in the vorticity direction. Both phenomena are in contradiction with the conclusions drawn for a pair of drops, and are, therefore, attributed to the elastic nature of the capsule interface. (c) 2008 American Institute of Physics.