STARTING VORTEX BEHIND A DISK NORMAL TO THE FLOW
A classical example of axisymmetric unsteady flow, this phenomenon precedes the establishment of a permanent regime, and
characterizes a starting movement.
The red streak that covers the front of the disk is emitted exactly at the point from which all streamlines are initiated
(that is, the stagnation point); along the side of the disk it turns green through dilution, and reveals the vortex structure
of the toroidal wake.
Image created by Henri Werlé. Reproduced with permission from his spectacular
collection Courants et Couleurs published in 1974 by ONERA, the French Aerospace Lab.
For further information, see
On the Flow of Fluids Made Visible,
Leonardo, Vol. 8, No. 4. (Autumn, 1975), pp. 329-331.