Abstract The interaction of moving fluids with particles is still only understood phenomenologically when the Reynolds number is not vanishing. I will present three different numerical studies all using the solver “fluent” which elucidate this issue from different points of view. On one hand, I will consider the case of fixed particles, i.e., a porous medium and present the distribution of channel openings, fluid velocities and fluxes. These distributions show a scaling law in the density of particles and for the fluxes follow an unexpected stretched exponential behavior. The next issue will be filtering, i.e., the release of massive tracer particles within this fluid. Interestingly, a critical Stokes number exists below which no particles are captured and which is characterized by a critical exponent of 1 2 . Finally, I will also show data on saltation, i.e., the motion of particles on a surface which when dragged by the fluid performs jumps. This is the classical eolian transport mechanism responsible for dune formation. The empirical relations between flux and wind velocity are reproduced and a scaling law of the deformed wind profile is presented.