Lagrangian dynamics of multiscale vortices in electromagnetically driven two-dimensional turbulence

Abstract

We experimentally investigate the dynamics of decomposed multiscale vortex cores (VCs) as singular objects of the two-dimensional (2D) turbulence driven by the Lorentz force from a direct current electric field and 2D magnetic lattice array. It is found that, in the xyt space, VCs of each mode (i.e., vortex spatial scale) appear as a zoo of unstable wiggling filament arrays with spatially alternating signs of vorticities. VC interaction and the chaotic external Lorentz force for vorticity injection and retraction lead to: (a) the spatial bunching of the VCs of adjacent modes, and the decaying position correlation of VCs with their separation and increasing mode number; (b) single VC dissociation and VC pair recombination, and in turn stretched exponential distributions of VC lifetimes of all modes; (c) similar persistent (super) diffusions of VCs of all modes, associated with persistent changes of the mean square vorticity fluctuations of VCs of the corresponding modes; and (d) the positively correlated instantaneous energy (enstrophy) variations between two neighboring VCs of modes 3 (the scale of the magnetic array for external vorticity injection and retraction) and its harmonics mode 4, and two-way instantaneous energy (enstrophy) exchange of the flow field surrounding VCs of modes 1–2 and modes 2–3.