Numerical investigations of colliding particles in spatially decaying turbulence

Numerical studies [10, 1] show that the influence of gravity and turbulence on the motion of small and heavy particles is not a simple superposition. However, in [9] it is shown that these studies may be artificially influenced by the turbulence forcing scheme. In the present study, a new numerical setup to investigate the combined effects of gravity and turbulence on the motion and collision probability of small and heavy particles is presented, where the turbulence is only forced at the inflow and is advected through the domain by a mean flow velocity. Within a transition region the turbulence develops to a physical state which shares similarities with grid-generated turbulence in wind tunnels. In this flow, trajectories of about 43 million particles are advanced in time. It is found that for specific particle inertia the particles fall faster in a turbulent flow compared with their fall velocity in quiescent flow. These results are in agreement with the theory in [4]. Additionally, specific regions within the turbulent vortices cannot be reached by the particles as a result of the particle vortex interaction. Therewith, the particles tend to cluster outside the vortices, which is called preferential concentration. Both effects alter the particle collision probability.