Axisymmetrization and vorticity-gradient intensification of an isolated two-dimensional vortex through filamentation

摘要: We consider the evolution of an isolated elliptical vortex in a weakly dissipative fluid. It is shown computationally that spatially smooth relaxes inviscidly towards axisymmetry on circulation timescale as result filament generation. Heuristically, we derive simple geometrical formula relating rate change aspect ratio particular vorticity contour to its orientation relative streamlines (where defined through second-order moments). Computational evidence obtained with diagnostic algorithms validates formula. By considering corotating frame and applying new formula, obtain detailed kinematic understanding vortex's decay final state primary secondary breaking. The transported into filaments although small fraction total, breaks symmetry chief cause axisymmetrization.