Settling of Diffusion-Limited-Aggregates in the Absence of Inertia

We study the settling of Diffusion-Limited-Aggregates as a model of marine aggregates and marine snow. The aggregates are assembled as a collection of cubic particles. The stresses on the surface and flow around the aggregates are computed in the limit of zero Reynolds number using a boundary integral method. We thus obtain an accurate representation of the flow around a fractal object. We compute the statistical distribution of the drag on the aggregate as a function of its size, and determine the corresponding effective radius. Time permitting, we will also present how a passive concentration, such as a low salt concentration, is advected by the flow, and how, within a porous aggregate, the concentration may change over time.