SIMULATIONS OF COAGULATION IN VISCOUS FLOWS

Hierarchical simulations described in this work predict structures for aggregates formed by rapid coagulation of particles in shear and extensional flows. The particles behave as sticky spheres, forming rigid bonds at contact, and the aggregates are assumed to follow bulk streamlines and rotate at the bulk vorticity until contact. We investigate cluster-cluster and particle-cluster aggregation as two distinct growth mechanisms, characterizing the structure by tracking particle-particle correlation functions, radii of gyration, and shape asymmetries. Upon comparing the results with experiments, one finds that the cluster-cluster simulations corroborate the similarity in structure observed experimentally for shear- and Brownian motion-induced coagulation; in both cases, the flocs have characteristics of fractals with dimension d = 1.8. Furthermore, the flow type does not affect the structure of cluster-cluster aggregates. On the other hand, the structures of particle-cluster aggregates differ from those measured and depend weakly on flow type. © 1991.