  The liquid cone-jet mode can be produced upon stimulation by a co-flowing gas
sheath. Most applications deal with the jet breakup, leading to either of two
droplet generation regimes: jetting and dripping. The cone-jet flow pattern is
explored by direct axisymmetric VOF numerical simulation; its evolution is
studied as the liquid flow-rate is increased around the jetting-dripping
transition. As observed in other focused flows such as electrospraying cones
upon steady thread emission, the flow displays a strong recirculating pattern
within the conical meniscus; it is shown to play a role on the stability of the
system, being a precursor to the onset of dripping. Close to the minimum liquid
flow rate for steady jetting, the recirculation cell penetrates into the feed
tube. Both the jet diameter and the size of the cell are accurately estimated
by a simple theoretical model. In addition, the transition from jetting to
dripping is numerically analyzed in detail in some illustrative cases, and
compared, to good agreement, with a set of experiments.
