Zhang, J. and Zhang, Q., 2015. Direct simulation of drag force on fractal flocs during settling.

The hydrodynamic drag force of fractal flocs during settling is examined by the Lattice Boltzmann method. Fractal flocs formed by Diffusion-Limited Aggregation (DLA) and diffusion-limited-cluster-cluster aggregation (DLCCA) models settle down in the quiescent water and drag forces are directly calculated. The numerical simulations are consistent with the analytical results. The ratio of drag force on fractal flocs and floc size shows a linear relationship with the floc settling velocity when the flow filed around the flocs is Stokes flow. The drag coefficient experienced by flocs is significantly different from the spheres. Moreover, drag forces on flocs formed by DLCCA are larger than flocs formed by DLA, when the flocs are composed of the same primary particles.