NUMERICAL CHARACTERIZATION OF THE DYNAMICS OF VORTEX FILAMENTS IN ROUND JETS

The dynamics of streamwise vorticity in axisymmetric jets is studied b y direct numerical integration of the Navier-Stokes equations coupled with a passive scalar. Consistently with recent experiments and invisc id numerical simulations, the present viscous simulations show the app earance of pairs of axially counter-rotating vortex filaments. After t heir formation the filaments move away from the jet, dragging the trac er into finger-shaped structures. The three-dimensional topology of th e rings, filaments, and fingers is described, well beyond the time of filament formation. Finally, visualizations of the pressure gradient f ield are presented, which suggest that the filaments can be directly o bserved experimentally by seeding the flow with microbubbles.