The rolling up of the vortex sheet that detaches along the free tip of a straight wing at incidence is a classical example of a stable concentrated vortex. The sense of rotation, diameter and pitch of the helical streamlines of the vortex core are revealed by liquid tracers of various colors. The very slow decay of this steady vortex may jeopardize airport operations.

Image created by Henri Werlé. Reproduced with permission from his spectacular collection Courants et Couleurs published in 1974 by ONERA, the French Aerospace Lab.