Explanation of differences in experimental and computational results for the preferential concentration of inertial particles

Using one-way coupled direct numerical simulations of inertial particles in homogeneous isotropic turbulence we investigate the non-linear dependence of local particle concentrations in particle clusters on the number density of particles used in the simulation per volume. We show that the Reynolds-number dependence of local concentrations in clusters can be predicted for sufficiently high Reynolds numbers by a scaling relation that depends on the average particle number density and the Kolmogorov length. Depending on the average particle number density and gravity, a maximum of preferential concentration does not necessarily occur at Stokes numbers around unity. This explains the differences observed between recent experimental and computational results.