Studies of the flow of a fluid with density differences caused by turbidity. August 1973.

Abstract

The mechanism of suspension of a non-buoyant particle in a turbulent flow has been examined from the viewpoint of the history of an individual particle. A program developed to compute trajectories of a non-buoyant particle within a field of eddies. The trajectories indicate that a particle may be suspended indefinitely within an individual eddy of the eddy field or may fall through the eddy field with a fall velocity which differs from the settling velocity of the particle in the quiscent fluid. The quantitative results are specific to the particular conditions examined. In a flow in which the net vertical flow of the fluid is zero, the time averaged fall velocity of a non-buoyant particle may differ from the settling velocity of the particle in the quiescent fluid and may be reduced to zero. In a series of experiments, rates of entrainment of fluids across a density discontinuity between two fluid layers have been measured. In these experiments, the turbulent flow of a fluid layer has been simulated by the motion induced by an oscillating grid. Density discontinuities due to temperature differences, salinity differences and the presence in one layer of suspended particles have been examined. The measured entrainment rates are consistent with the hypothesis that under given conditions the rate of entrainment is dependent upon the molecular diffusitivity of the property causing the the density discontinuity