https://iopscience.iop.org/article/10.1016/0169-5983(93)90106-K/pdf

Phenomena of liquid drop impact on solid and liquid surfaces

Some drops don't splash

Drops falling certain distances before impact with a pool of the same liquid produce vortex rings that penetrate more deeply into the pool. As a drop falls it oscillates in shape between prolate and oblate through spherical. Earlier researchers have stated that a spherical shape changing to prolate correlates with maximum vortex ring penetration and a spherical shape changing to oblate with minimum penetration. The work reported here in which the drop shape on impact was photographed does not support these views. Analysis of high-speed motion pictures of drop impact reveals that the shape of the crater caused by drop impact exerts a crucial influence on how deeply the drop-formed vortex ring penetrates the pool. A narrow crater formed by the impact of a prolate-shaped drop accompanies maximum vortex ring penetration. The narrow crater appears to aid vortex ring formation with minimum subsequent distortion and helps the vortex ring to detach readily from the crater.

The penetration of drop-formed vortex rings into pools of liquid

Observations are reported for the three‐dimensional vortex structure created by a dyed water drop impacting a pool of water. The structure and evolution of the vorticity is studied for a Weber number of 22–25 and a Froude number of 25–28. The drop and pool do not make first contact at the bottom of the drop but at latitudes away from the bottom pole of the drop. This traps a thin, curved, pancake‐shaped air bubble beneath the drop which rapidly contracts into a sphere. As the drop impacts the pool its impulse produces vorticity which rolls up into a primary vortex ring. As the vortex ring travels down through the pool, vortex filaments extend from the central axis of the vortex ring to form a ‘‘stalk.’’ This reaches from the primary ring to another ring of vorticity which has formed in the now reversing free surface impact crater. As the primary ring convects downward some vortex filaments undergo an azimuthal instability which grows until the filaments escape the trapped orbits of the primary vortex ring...

Hugh Forrest. Keedy

Papers

Vortex rings formed by free surface interaction