Drop Penetration through a Constriction: Effect of Surrounding Fluid

In this study, we examine the effect of surrounding liquid on the motion of gravity-driven drops through a round-edged circular orifice using high-speed visualization and refractive index matched PIV. The overall motion of the drop is separated into three stages: pre-impact, penetration and release. We show that in liquid/liquid systems, the surrounding fluid influences the drop velocity during both pre-impact and release stages. During the pre-impact stage, the drop approaches the orifice by displacing the surrounding liquid radially across the plate as well as axially through the orifice. During the release stage on the other hand, surrounding fluid is drawn downward into the orifice as the drop exits below the plate. In both cases, the drop decelerates due to added mass and viscous effects, which are negligible in liquid/gas flows. Drop breakup is promotedby a higher viscosity surrounding such that the volume of the satellite drop increases when the drop-to-surrounding-fluid viscosity ratio is decreased.