Pinch-off modes and satellite formation in liquid/liquid jet systems

Forced jets of glycerin/water solution flowing into silicone oil were investigated. Forcing amplitudes were sufficient to induce stable or semi-stable pinch-off modes in the jet. The indices of refraction in the two liquids were matched, and planar slices of flow were visualized using laser induced fluorescence. Two-dimensional velocity fields were obtained by particle image velocimetry (PIV). For a viscosity ratio, ηi/ηo=1.6, satellites form at lower Reynolds numbers as well as lower Strouhal numbers. Satellite occurrence depends on the interface shape approaching pinch-off as well as the detailed velocity gradients surrounding the pinch-off region. Satellite formation required a zone of concave curvature downstream of but close to the jet neck as pinch-off approached. This zone was associated with intense vorticity that first deformed the interface into an upstream-facing cone attached to the main drop and then deformed the cone into a satellite shape. Increasing the ambient viscosity suppressed satellite formation for the Reynolds and Strouhal numbers examined.