Three-dimensional CFD simulation of the flow field around and through particle aggregates

The hydrodynamic properties of fractal aggregates in a flow field were investigated by the numerical method of computational fluid dynamics. The sample aggregates were constructed with a self-similar scaling structure. Therefore, the morphological information about the aggregates, such as fractal dimension, porosity, compactness, and the internal and external region, can be determined from the fractal structure. Navier–Stokes equations were applied to the whole flow field in relation to the aggregate, including both the exterior flow around and the interior flow through the aggregate. With the CFD, the flow velocity vectors and the streamlines around the fractal aggregates of different structures under different flow conditions can be well simulated. The results show that fractal aggregates are permeable and flow through permeable aggregates can effectively reduce the drag forces of the aggregates. The fractal dimension has a profound effect on the internal permeation of the aggregates. The fluid collection efficiency can increase from about 0.1 for the aggregates with a fractal dimension of 2.7 to more than 0.6 for the aggregates with a low fractal dimension of 1.1. The permeability of the aggregates increases considerably as they become more porous with a higher porosity. On the other hand, however, for a given type of the aggregate structure, the fluid collection efficiency of the aggregates does not appear to change significantly with the size of the aggregates.