New approaches to vortex dynamics: core dynamics, helical waves, and interaction with fine scale turbulence

Some new aspects of vortex dynamics, coherent structures and interaction with fine-scale turbulence are reviewed. In the absence of any appropriate measurement technology for the 3-D instantaneous vorticity field we rely on direct numerical simulation of the Navier-Stokes equations using spectral methods in an 128"SUP 3" periodic cube. We study first the evolution of a laminar vortex column with a nonuniform core at a Reynolds number RE identical to GAMMA/nu=665, and then the vortex's evolution in the presence of fine-scale homogeneous, isotropic turbulence. We show that core dynamics, ignored so far, can be very significant in vortex dynamics and vortex interactions and consists of travelling vorticity wave packets along the vortex axis. We also show that core dynamics can be better explained by complex helical wave decomposition - a new mathematical tool - than in terms of coupling between swirl and meridional flows. (from Author)