Coupling of a Vortex with Turbulence - Limitation of Core Dynamics and Bursting

Variation in the vortex core diameter inherently drives vortex line coiling/uncoiling, called core dynamics, associated with meridional flow – radial and axial velocities. Data for large core variations show coiled vortex lines with azimuthal vorticity (ω_θ) forming packets, which collide and result in a vortex ring dipole; the eruption of this dipole is called vortex bursting. The dipole is unstable, thus the question of how turbulence couples with core dynamics and bursting arises – studied here using DNS at a Reynolds number (vortex circulation/viscosity) of 10,000 – the limit of current computation. Core dynamics couple with the turbulence via the meridional flow. Meridional flow tilting of vorticity is the most dominant mechanism within the core, as the mean strain tilting is negligible. Notably, generation of radial vorticity (ω_r) alters vortex line coiling, which causes the packet to be diffused. This is most impactful when the packets collide to form the dipole. Tilting of the turbulent ω_r locally generates positive and negative ω_θ – hence, the packet transforms into a clustering of fine scale ω_θ regions. The disruption of the packet interrupts the dipole formation and prevents bursting – an obstacle to using bursting for control of aircraft trailing vortices.