Analysis of Turbulence Suppression in Sediment-laden Saline Currents

Abstract

The present work extends the results of Cantero et al.[1] and Shringarpure et al.[2] to the cases of sediment-laden saline currents. The flow is modeled as a channel flow where the forcing is exerted by salinity and suspended sediments. The resulting set of equations are solved by direct numerical simulation (DNS) for shear Reynolds number Reτ = 180. The DNS results show that by increasing the forcing due salinity, the flow can be held in a turbulent state whereby large sediment particles can be maintained in suspension. Typically, such large sediment particles would not be able to sustain the flow by themselves. The DNS results also show that for large sediment loads there is a transition to total turbulence suppression. This transition is abrupt and is caused by small changes in the sediment load. Here, salinity can be interpreted as a fraction of sediments that are fine enough that their settling velocity is negligible. Thus, the case of sediment-laden saline currents is physically equivalent to a simplified bi-disperse model where the fine sediments do not settle. Finally, this work shows that the original results by Cantero et al.[1] and Shringarpure et al.[2] hold when they are reinterpreted under the light on an effective settling velocity.