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Fig. 1. Diagram of a vortex ring in cross section with the X' and
Y' axes indicated, velocity components and velocity profiles.
(A) Cross section of vortex ring left behind by the frog foot just
disappearing on the left. Red, clockwise vorticity; blue, anti-clockwise
vorticity; Y'-axis is normal to the vortex ring;
X'-axis is perpendicular to the normal axis, parallel to the
ring plane. (B) Predicted v velocity profile along the
Y'-axis. (C) Predicted u velocity profile through vortex
core along the Y'-axis. (D) Predicted v velocity profile
along the X'-axis through both vortex cores.