Atomization patterns produced by the oblique collision of two Newtonian liquid jets

Abstract

This paper reports a detailed experimental investigation of the formation, destabilization, and atomization of the liquid sheets created by the oblique impact of two laminar jets of a Newtonian liquid. Glycerol-water mixtures with viscosities between 4 and 30 mPa s were used to investigate the effects of viscosity and jet velocity. The jets were ejected from parallel cylindrical nozzles with an internal diameter of 0.85 mm. Collision of the jets resulted in various regimes of behavior which depend on the jet velocities and the liquid properties. We focus on the regime where the impinging jets form a liquid sheet which then breaks up into a regular succession of ligaments and droplets, a so-called "fishbone" pattern. We use short-duration, single-flash illumination combined with high-resolution digital photography to study the evolution of the sheet, its shape, and the form, size, and spacing of resulting ligaments and drops. Unexpectedly, we found fishbone regimes corresponding to lower Reynolds and Weber numbers than had been previously reported; furthermore our apparently symmetric fishbone structures were definitely associated with asymmetric, rather than symmetric, impacting jet conditions. The fishbone structure was found to be significantly affected by any asymmetry in either the free lengths of the two jets or their alignment. The fishbone angle, defined as the angle between the lines through the first pairs of droplets on each side of the fishbone structure, is introduced to describe the effects of differences in jet length, alignment, or fluid properties on the degree of development of the fishbone pattern. We discuss how changes in the various parameters influence the form of the fishbone pattern and the origin and mechanism of the periodic atomization of the sheet. In particular we find that the dependence of the drop spacing on viscosities is consistent with the Rayleigh-Plateau instability on the rim provided the variation of the rim width is properly included, as this dominates the Ohnesorge number dependence of the breakup.