Finite Element Simulations of Colloidal Aggregates under Shear Flow Conditions

We perform finite element simulations of aggregates in shear flow environments, in order to improve the model of hydrodynamic forces used for discrete element simulations. The mechanistic model for the discrete element simulations implies until now the so-called free-draining approximation for the fluid forces which is a drastic simplification. From the finite element simulations we extract the fluid forces acting on the constituents of small aggregates of 8 to 20 particles. With these highly-resolved results we can extract parameters for the hydrodynamic force model. We find two major results: first, inside the aggregates the fluid flow is relaxed and can for the small aggregates be parameterized by an effective shear rate which is significantly smaller than the ambient shear rate, while for the large aggregates, a core-shell model is proposed; and second, the flow field in the core region of the aggregates is not aligned with the external flow, which is the case for the forces acting on the shell particles.