The sedimentation of flexible filaments: Trajectories, particle clouds and a buckling instability

In this fluid dynamics video we explore an array of different possible dynamics for a flexible filament sedimenting in a viscous fluid. The time-dependent shapes and trajectories of the filament are determined analytically and numerically by balancing viscous, elastic and gravitational forces in a slender-body theory for zero-Reynolds number flows. The dynamics are characterized by a single dimensionless elasto-gravitation number. The video shows the process of filament relaxation and reorientation, the formation of particle clouds, and finally a buckling instability.