Settling dynamics of inertial disks in turbulence

Sedimentation of solid particles is encountered in engineering and environmental flows, yet the dynamics of finite-size particles in homogeneous anisotropic turbulence is still not fully understood. We perform experiments of disks falling in quiescent flow under different regimes, and compare their dynamics with the results from sedimentation under turbulent environments. We use two facing random jet arrays (RJA) of water pumps to generate turbulence with negligible mean flow and shear over a volume that is much larger than the initial characteristic turbulent large scale of the flow. The Reynolds number for forced turbulence is Re_λ≈580 and the axial-to-radial ratio of the rms velocity fluctuations is 1.22. The turbulence decay is investigated by monitoring velocity fluctuations, dissipation and turbulent length scales over time and disks are released at different decay times. The solid to fluid density ratio range is 2.7 to 7.5 and the particle diameter is of the same order of magnitude as the Taylor microscale. Turbulence has a severe influence on the settling dynamics of disks, modifying the mean velocity and the particle lateral dispersion; and introducing fast and slow events on the particle descent that are captured in the frequency content of the velocity fluctuations.