Gravitatory settling of inertial particles in turbulent environments

Turbulent flows laden with particles are important for both environmental phenomena and industrial systems. This study focuses on dense sub-Kolmogorov inertial particles in a homogeneous and isotropic turbulent gas flow. Experimental measurements of particle vertical and horizontal velocities were taken via a Phase Doppler Interferometer. A wide range of Taylor Reynolds numbers (Re_λ ∈ [30-520]), Rouse numbers (Ro ∈ [0-5]) and volume fractions (φ_v ∈ [0.5×10^-5 - 2.0×10^-5]) were explored. Three types of grid turbulence were tested by means of a passive grid and an active grid used in two different modes (grid shafts moving randomly or open in a static configuration). This work aims at studying the role of the carrier phase Taylor Reynolds number, Rouse number and volume fraction on the settling velocity of inertial particles. We find, in agreement with previous work, that enhancement of the settling velocity occurs at low Rouse number, while hindering of the settling occurs at higher Rouse number for a decreasing turbulence energy levels (characterized by the velocity fluctuating intensity or the Taylor Reynolds number). The wide range of flow parameters explored allowed us to observe that enhancement decreases significantly with the Taylor Reynolds number.