A LID-DRIVEN ELONGATED ANNULAR FLUME (LEAF) FOR THE DETERMINATION OF SEDIMENT TRANSPORT PROPERTIES

摘要

Predictions of the fate and transport of sediment are possible only if the properties of near-bed erosion and deposition of the sediment are known. These properties are the erosion rate, deposition rate that is the product of the settling velocity and the sediment concentration, and the critical shear stresses of erosion and deposition. The properties can be determined in laboratories using reconstructed seabed sediments and known flow-generated shear stresses. For cohesive sediment experiments, circular annular flumes with rotating lids are popularly used to avoid disturbing the interaction between particles in the water column. The major drawback of this type of flume is the centrifugal acceleration which causes the cross-sectional velocity distribution to become non-uniform. A Lid-driven Elongated Annular Flume (LEAF), designed to reduce the centrifugal effect, has been built. Figure 1 is a picture of LEAF. The flume has two identical 3-m long straight sections which are meant to create a uniform flow environment. The 2 semi-circle sections have an inner radius of 0.2m and an outside radius of 0.4m. The flow width of the flume is 0.2m. The width of the lid is approximately 0.2m which is almost equal to that of the flume. The water depth and vertical position of the lid can be adjusted freely. The lid is driven by an adjustable speed motor. This paper presents a numerical study of the hydrodynamic characteristics and an experimental study of the sediment transport behavior in LEAF.