Experimental investigation of particle deposition inside a cavity by PIV technique

Particles sedimentation is an important theme in coastal and fluvial engineering and in environmental engineering due to the significant presence in nature in the form of dust storms, dispersion of atmospheric aerosol, water pollution and particle transport in general. In this dissertation the process of particles deposition inside a rectangular cavity on the bottom of a channel is studied. Experiments have been performed by varying Reynolds numbers (3500, 4000 and 4500) and particle size as well. The fluid field is investigated by ‘Particle Image Velocimetry’ technique, which is an optical method to obtain flow field velocities indirectly by measuring the velocity of a tracer within the flow, which consists of pollen of diameter of 150-250 micrometer. The presence of the cavity generates vortical structures, which develop near the upstream corner of the cavity and move in the flow direction till the downstream corner. The deposition process is investigated by seeding the fluid flow with heavy particles of diameter of 170-180 micrometer and 180-200 micrometer through a hopper slide upstream of the cavity. As the cavity area is reduced by the particle deposition the fluid fluid changes because the bottom boundary evolves thus feedback on the particles dynamics occurs. The strong vertical fluid velocity component due to the upstream corner eddy deflects the particle trajectories and determines the deposition inside the cavity. The influence of the bottom evolution cannot be neglected: the increasing elevation of the bottom geometry enhances the deposition. The results of this work will be used to validate the model of sediment by Bozzi and Passoni (2012). In the future solid trajectories will be investigated by ‘Particle Tracking Velocimetry’ technique.