Turbulent particle-laden flows are prevalent in both industrial and natural processes. Among the various consequences of inertial particle-turbulence interactions, preferential concentration and the modification of particle settling velocity have received considerable attention in recent decades. Preferential concentration refers to the tendency of particles to accumulate in space, forming clusters and voids. In contrast, particle settling modification accounts for the enhancement or hindering of the particles' settling velocity in the direction of gravity. This system is highly non-linear and out of equilibrium, requiring a Lagrangian approach, both theoretically and experimentally.

Surprisingly, current modeling capabilities are still so limited that we cannot yet answer simple questions, such as: Do small spherical particles in a turbulent environment settle slower, faster, or at the same velocity as in a quiescent fluid? What is the statistical spatial distribution of particles in a turbulent flow?

We will discuss recent experiments conducted in a wind tunnel. Using a set of turbulence-generating grids, both passive and active, we explored different inflows and particle inertia, covering a broad range of the parameter space. High-speed imaging and a phase Doppler particle analyzer were used to characterize preferential concentration and settling velocities, respectively. Our results, which highlight the relevance of large scales in both phenomena, will be discussed in the context of existing models.