Visualizations reveal the almost conical character of the flow around the apex on the upper surface: the stream sheet that separates from the leading edge on each side of the wing rolls up as "scrolls" to make up the core of the main vortex. The colored streaks emitted along the leading edge show the helical structure of the main vortex and the existence of a secondary vortex, while the emissions on the wing surface (in red) emphasise the median zone of clean flow. The existence and organisation of these scroll vortices were brought to light for the first time at ONERA in 1951.

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