Planar Particles in Quiescent Fluid
The aim of this chapter is to investigate experimentally the effect of the frontal geometry on the settling dynamics of planar particles in quiescent flow. The question “What if the disc has a wavy edge?” formulated in Moffat (J Fluid Mech 720:1–4, 2013) is extended here not only to sinusoidal edge particles but to sharp edge polygons and three studies are combined to tackle this question. First, particle tracking experiments of disk-like particles with the perimeter described by sinusoidal functions are performed. We differentiate trajectories according to the degree of out of plane motion and obtain a drag correlation function that depends on the particle geometry. Second, trajectories of N-sided polygons with the same material properties and frontal area but different number of sides are also investigated by particle tracking experiments and a simple pendulum model is found to represent accurately the descent motion of these particles once the mean descent velocity is known. Finally, we perform measurements of the instantaneous three-dimensional velocity field on the wake of several of these polygons. We observe severe differences in the shedding mechanisms and these are related to the descent style of the particles.
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