Figure 2
Left: Multiple exposure visualisation of the vortex ring in the horizontal plane. Right: In-plane velocity vector field induced by the travelling vortex ring. The additional contour lines show the velocity magnitude and start from 1/10 \(U_0\) in steps of 1/5 \(U_0\), where \(U_0\) is the travel speed of the vortex ring. The color-coded vorticity field highlights the cores as regions of highest magnitude of vorticity, which represent the cuts through the toroidal core of diameter \(D_c\) = 24 mm. The dashed circular ring approximates the outer diameter \(D_o\) of the ring, beyond which fluid has remained nearly stagnant with velocities lower than 1/10 \(U_0\).
