Gravitational settling of particles and bubbles in homogeneous turbulence

I investigate whether, in general, the average settling velocity of a small particle/bubble subject to a square drag force in homogeneous, stationary turbulence with a Kolmogorov spectrum differs from that in still fluid and, in particular, the role played by the structures of the flow field. I study particle or bubble trajectories in a simple flow structure. Statistics have been computed for the motion of small particles/bubbles settling under gravity with a Gaussian random velocity generated by Fourier modes. As a main result it is shown that homogeneous turbulence does cause a net decrease of settling velocity in the case VT/u' ∼ O(1).