Flow Structure Over a Simulated Bed for Costal Cohesive Sediment Erosion Studies

This paper reports an experimental assessment of various alternatives to construct an artificial bed appropriate to duplicate, in laboratory, the conditions relevant to marine sediment erosion. The main goal of the study is to find a simulated bed that approaches the behavior of natural sediments, based on the velocity and turbulence profiles and on the interface shear stress values. For that purpose, experiments on natural sediments collected in two estuaries and on a variety of artificial beds were carried out in a circular mini flume, 131 mm in diameter. Velocity profiles and turbulence data were taken by means of a two-component LDA system at a Reynolds number of 20,000. For artificial sediments both rigid and deformable (either fluid or grain) surfaces were investigated. The results show that bed deformation plays an important role in controlling shear stress. The use of two liquid layers simulated bed does not appear to be an appropriate option due to the very high deformation at the interface of the layers. Rigid surfaces that replicate sediment morphology may be appropriate for the simulation of highly cohesive sediments. Turbulence structure proved to be a wall driven phenomenon, except for very dense dispersed flows.