Dynamics of a liquid film flowing down a granular chain

A liquid film flowing down a fibre becomes unstable, leading to the formation of droplets that travel downstream. The droplet spacing and speed depend on the flow rate for a given nozzle and fibre radii. We show that fibre morphology further modifies the droplet spacing. In particular, we study the effect of the size of the beads in a granular chain on the evolution of the film thickness. We show that, when the size of the bead exceeds a critical value, the selection mechanism for instability modes is modified from regularly spaced droplets to coarsening by droplet merging. Droplet formation for flow over a single bead on the fibre is modified successively over subsequent beads in the downstream. Further, we show that if the perturbation in the flow produced by the bead is introduced as a velocity perturbation at the nozzle inlet, the formation of droplets on the fibre is qualitatively similar to that for the bead.