COMPARISONS OF DYE PLUME MIGRATION AT THE NEAR-WALL REGION OF TWO DIFFERENT FLAT BEDS ROUGHENED WITH 7 MM AND 10 MM SYNTHETIC PLEXIGLAS BEADS

The detection of moving particles and the ability of processing the captured images using high-speed cameras can be an effective means of monitoring the sliding, and rolling movement of bed-load sediment along river beds. In this study, two different types of synthetic Plexiglas Beads of size 7mm and 10mm with porosity 0.7125 and 0.8522 respectively were used for the evaluation of the velocity profiles in a flume bath. Potassium permanganate (KMnO4) crystal of molecular weight 158.03 and density 1450 kg/m3 was used as a passive dye-tracer. The cavity region of the flat plate was attached to the oscillatory mechanism in the flume bath where plume activities were monitored. When there is oscillatory flow, the crest of roughness elements induce elevation zones to force (advection) the flow upwards and pull it down at the trough phases as the tracer plume scales over the obstacles, establishing low and high pressure zones in the flow. The enhanced particles in the process mix and dissolve or decay faster with increasing oscillatory frequency, resulting into inter-particle collisions which initiate the conditions of advection and shear dispersion. This phenomenon could be a combination or coupling of the processes of gradient fluctuations enhanced through dispersion due to pressure in the macroscopic pore-fluid field caused by the oscillatory motion. The lightening as the dye-particles cascade in the porous medium is associated with mixing-gain due to the enhanced oscillatory motion. It was observed that the depth of the tracer-blob entrapment is inversely proportional to the friction velocity.