A vortex ring generation geometry that has been cited as a standard consists of the tube exit mounted flush with a wall with the piston stroke ending at the tube exit. We employ this geometry to investigate the effect of the vortex that forms in front of the advancing piston (piston vortex) on the primary vortex ring that is formed at the tube exit. It is shown that when the piston finishes its stroke flush with the wall, and hence forms an uninterrupted plane, the piston vortex is convected through the primary ring and then ingested into the primary vortex. The ingestion of the piston vortex results in an increased ring impulse and an altered trajectory, when compared to the case when the piston motion is finished inside the tube. The photograph, at the instant the piston motion has ceased, shows the primary ring and the piston vortex.

The work was sponsored by the National Science Foundation.

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