Fluid-particle coupling in dilute suspension releases

In this paper we shall present consistent scaling arguments leading to the development of various distinguished limit models for the study of particle suspension flows as produced in the classic lock-release experiments that are designed to illuminate the mechanisms of rarely observed submarine turbidity currents. We shall show that very dilute suspensions lead to a decoupling of fluid and particle dynamics and allow for a consistent description in terms of two-layer, shallow-water (hydraulic) theory, Moodie ct al. [1] and Moodie [2]. This class of models, when applied to the study of particle transport and deposition from bottom gravity currents produced by the sudden release of dilute, well-mixed fixed-volume suspensions have been relatively successful in predicting the experimentally observed longtime, distal, areal density of the deposit on a rigid horizontal bottom. These models, however, fail in their ability to capture the experimentally observed proximal pattern of the areal density with its pronounced dip in the region initially occupied by the well-mixed suspension and its equally pronounced local maximum at roughly the one third point of the total reach of the deposit in many experiments. We shall here show how to modify the assumptions of Moodie et al. [1] and Bonnecaze et al. [3,4,5] to account for the presence of initial turbulent energy of mixing in the release volume and thereby obtain better agreement with experimental results. We shall also outline an approach for relaxing the severe constraint on the dilute nature of these suspensions.