Vortex ring generation during drop impact into a shallow pool

TL;DR

This study investigates the formation and behavior of vortex rings generated when a drop impacts a shallow pool, revealing their characteristics, stability, and dependence on experimental parameters.

Contribution

The paper provides detailed experimental analysis of vortex ring generation during drop impact into shallow pools, highlighting their formation, circulation, stability, and parameter sensitivities.

Findings

Two pairs of vortex rings are generated during impact.

Each pair includes a short-lived and a persistent ring.

Ring circulation signs are opposite to those in deep-water impacts.

Abstract

When a drop falls from a moderate height into a shallow fluid pool whose depth is of the order of the drop-radius two pairs of vortex rings are generated. The inner pair forms at the edge of the crater created by the impacting drop while the outer pair is laid off from the spreading wave. One ring of each of these pairs is short-lived while the other persists. Each of the rings has a measureable non-zero circulation (whose sign, however, is opposite to that of the well-known deep-water drop vortex rings) which persists long after the wave has receded. Furthermore under certain conditions they develop instabilities typical to ring vortices. Although the rings are well reproducible, aspects of their later development are very sensitive to changes in some of the experimental parameters. This paper reports on experiments distinguishing reproducible aspects of these drop- generated rings and documenting their dependence on material and geometrical parameters.