(505a) A Cloud of Rigid Rods Sedimenting in Viscous Fluid

We investigate the deformation and breakup of a cloud of rigid, rodlike particles falling under gravity through a viscous fluid in the absence of inertia and interfacial tension. Results from dynamic simulations which include hydrodynamic interaction demonstrate that an initially spherical cloud of rigid rods rapidly evolves into a torus which then shatters into secondary droplets. These smaller droplets, in turn, transition into tori and again break apart in a cascade of events that repeats many times. However, the fluctuations in the velocities and positions of the rods accelerates the breakup process as compared to drops of liquids or spherical particles. The simulation results compare well with experimental visualizations of a cloud of sedimenting rods.