Three-dimensional instability during vortex merging

Patrice Meunier (1) , Thomas Leweke (1)

1 IRPHE - Institut de Recherche sur les Phénomènes Hors Equilibre

The interaction of two parallel vortices of equal circulation is observed experimentally. For low Reynolds numbers ($Re$), the vortices remain two-dimensional and merge into a single one, when their time-dependent core size exceeds approximately 30\% of the vortex separation distance. At higher $Re$, a three-dimensional instability is discovered, showing the characteristics of an elliptic instability of the vortex cores. The instability rapidly generates small-scale turbulent motion, which initiates merging for smaller core sizes and produces a bigger final vortex than for laminar 2D flow.

Mots clés: fusion; vortex; instabilité elliptique

Domaines: Mécanique des fluides [physics.class-ph]; Mécanique des fluides [physics.class-ph]

Patrice Meunier, Thomas Leweke. Three-dimensional instability during vortex merging. Physics of Fluids, 2001, 13, n° 10, p. 2747-2750. ⟨10.1063/1.1399033⟩. ⟨hal-00081686⟩