  We investigate velocity variations inside of and surrounding a gravity driven
drop impacting on and moving through a confining orifice, wherein the effects
of edge geometry (round- vs. sharp-edged) and surface wettability (hydrophobic
vs. hydrophilic) of the orifice are considered. Using refractive index matching
and time-resolved PIV, we quantify the redistribution of energy in the drop and
the surrounding fluid during the drop's impact and motion through a round-edged
orifice. The measurements show the importance of a) drop kinetic energy
transferred to and dissipated within the surrounding liquid, and b) the drop
kinetic energy due to internal deformation and rotation during impact and
passage through the orifice. While a rounded orifice edge prevents contact
between the drop and orifice surface, a sharp edge promotes contact immediately
upon impact, changing the near surface flow field as well as the drop passage
dynamics. For a sharp-edged hydrophobic orifice, the contact lines remain
localized near the orifice edge, but slipping and pinning strongly affect the
drop propagation and outcome. For a sharp-edged hydrophilic orifice, on the
other hand, the contact lines propagate away from the orifice edge, and their
motion is coupled with the global velocity fields in the drop and the
surrounding fluid. By examining the contact line propagation over a hydrophilic
orifice surface with minimal drop penetration, we characterize two stages of
drop spreading that exhibit power-law dependence with variable exponent. In the
first stage, the contact line propagates under the influence of impact inertia
and gravity. In the second stage, inertial influence subsides, and the contact
line propagates mainly due to wettability.
