This study numerically evaluates the hydrodynamic drag force exerted on a porous sphere moving through a Newtonian fluid towards an impermeable flat plate at a Reynolds number ranging from 0.1 to 40. The sphere is assumed to be highly porous, whose interior flow field is modeled by the combined Darcy–Brinkman model. The surrounding fluid flow field is governed by steady-state Navier–Stokes equations. When the floc permeability is rather high, which is common for sludge flocs, no boundary layer separation occurs in the after-sphere region at large Reynolds numbers. The drag force thereby adheres to a Stokes’ law like relationship.
