2019_EJRNL_PP_PAUL_A__JARVIS_1.pdf
Terbatas Ratnasari
» ITB
Terbatas Ratnasari
» ITB
The low-Reynolds-number gravitational settling of a sphere through a fluid interface
is investigated experimentally. By varying the viscosity ratio between the two fluids and
the Bond number, two different modes of interfacial deformation are observed: a tailing
mode and a film drainage mode. In the tailing mode, the interface deforms significantly
as the sphere approaches, and the sphere becomes enveloped by a layer of the upper fluid.
A tail forms, connecting the sphere to the bulk of the upper phase. In the film drainage
mode, the interface deforms much less and the sphere impacts onto the interface, which
either ruptures to form a contact line on the sphere or leaves a very thin wetting film.
Additionally, two types of sinking profiles are observed: steady sinking, where the sphere
velocity changes monotonically as it sinks, and stalled sinking, where the sphere’s progress
is inhibited by the interface, before it accelerates into the lower fluid. We present a regime
diagram showing the different behaviors. Finally, the dependence of the sinking time on
the Bond number and viscosity ratio is investigated. For the film drainage regime a simple
scaling law is deduced; the tailing regime exhibits more complicated dynamics, possibly
explained by a multistage sinking process.