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Title: Far wake of a delta wing

Description: A great many studies have been directed towards understanding the flow over wings and, in particular, over a delta wing. Very surprisingly indeed, in our view, there exists no visualizations, from the laboratory, of the far-field development of the trailing vortex pair as it travels downstream, to our knowledge. Our flow visualization, involving novel free-flight gliding of a delta wing in water, shows for the first time, the exquisitely beautiful structure of the turbulent wake, in side view. One should note that these photographs are all to closely the same scale! The fluorescene dye, illuminated by a laser, shows that the near wake comprises an interaction between the primary streamwise vortex pair with the 'braid' wake vortices between the pair. Far downstream (64 chordlengths behind the wing) the primary vortex pair has reconnected and become large-scale rings (lower picture), although with a distinctly smaller length scale than predicted from the analysis of Crow. See also delta wing in free flight and break-down of a vortex pair.

Credits: C. H. K. Williamson

References: Crow S.C. (1970) Stability theory of a pair of trailing vortices. AIAA J. 8, 2172.

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