Suspension and fall of heavy particles in random two-dimensional flow

We investigate the settling of heavy particles in a steady, two-dimensional random velocity field, and find instances in which particle suspension occurs. This leads to a bimodal velocity distribution that may explain some apparently conflicting results reported in the literature. The bimodal distribution is typically smeared out by a time-dependence of the ambient flow but, if the time-variation is slow, the settling rates of some particles will be as well. The resulting broad-banded velocity distribution of the settling particles will have significance for processes such as rain drop formation, in which the spread of particle velocities affects the statistics of particle collisions.