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.