  In unresolved flow CFD-DEM simulations, the porosity values for each CFD cell
are determined using a coarse-graining algorithm. While this approach enables
coupled simulations of representative numbers of particles, the influence of
the porosity local to the particles on the fluid-particle interaction force is
not captured. This contribution considers a two-grid coarse-graining method
that determines a local porosity for each particle using a radical Voronoi
tessellation of the system. A relatively fine, regular point cloud is used to
map these local porosity data to the CFD cells. The method is evaluated using
two different cases considering both disperse and tightly packed particles. The
data show that the method conserves porosity data, is reasonably
grid-independent and can generate a relatively smooth porosity field. The new
method can more accurately predict the fluid-particle interactive force for
polydisperse particle system than alternative methods that have been
implemented in unresolved CFD-DEM codes.
