  Here we report experiments on particle cluster settling at high Reynolds
number in quiescent fluid contained in a vessel. The particles were observed to
settle in a near-circular shape irrespective of the shape of the vessel
cross-section and particle shape, size, and types. Effect of different
parameters such as mass, type and aspect ratio of the particles, height, and
viscosity of liquid was investigated. Formation of the hemispherical bottom cap
of the cluster that bounces upon hitting the vessel bottom surface was found to
be responsible for the final circular shape of the settled structure. Particle
leakage from the cluster was seen in the form of a tail. In the liquid having
viscosity beyond 100 cP, cluster breakage was observed that resulted in
hindered settling and asymmetric shapes of finally settled particles. The
observations are useful to understand the overall area over which settling of
such clusters can be observed.
