Density distribution effects on the settling dynamics of nonspherical inertial particles at intermediate Reynolds numbers

Many settling, large, nonspherical particles of interest (e.g. naturally occurring aggregates) do not have a uniform density. Here we investigate the orientation and terminal velocity of freely falling uniform- and compound-density cylinders with relatively low aspect ratios (from 1 to 4) at intermediate Reynolds numbers (on the order of 100). Agarose gel with varying density and aluminum molds were used to fabricate hydrogel cylinders. All cylinders had an average specific gravity (SG) of 1.005. Two layers of gel, one with a SG of 1.003 adhered to a second layer with a SG of 1.007, were used to create the compound-density cylinders. The cylinders were released at the top of a 56 cm tall hexagonal tank filled with still water and imaged simultaneously by two high-speed cameras. Two additional low-speed cameras captured the full trajectory of each cylinder along with their landing position. The terminal velocity, fall orientation, and landing site of the cylinders were recorded and periodicity in the settling behavior of each cylinder was analyzed. Preliminary results show significant differences in the settling characteristics of uniform- vs. compound-density cylinders. These results have large implications for predicting the settling behavior of naturally-occurring particles.