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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.
Reference:
Allen,
J. J. & Auvity, B. Interaction of a vortex ring with a piston vortex.
Journal of Fluid Mechanics, February 2002.
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