Spreading of an inviscid drop impacting on a liquid film

Abstract

The evolution of the deforming liquid surface following the impact of a drop onto a film of the same liquid is analysed numerically using a boundary integral method assuming axisymmetric, inviscid flow. Surface tension and gravity are taken into account. At times comparable to, or larger than the impact time scale (based on initial drop radius and impact velocity), the section of the liquid surface bounded by the radially propagating crown or rim is predicted to approach a single central shape independent of film thickness. At times which are much smaller than the impact time scale, jetting behaviour is obtained in the neck region where the drop meets the film when the Weber number is large enough. The jet is found to move close to the film, and this suggests the possibility of bubble entrapment, confirming a previous report in the literature. The present results suggest the occurrence of a train of bubble rings from repeated near-reconnection events as the neck moves radially outwards under jetting conditions.