Meandering dynamics of streamwise vortex pairs in afterbody wakes (original) (raw)

Wakes of upswept afterbodies are often characterized by a counter-rotating streamwise vortex pair. The unsteady dynamics of these vortices are examined with a spatiotemporally resolved Large-Eddy Simulation (LES) dataset on a representative configuration consisting of a cylinder with upswept basal surface. Emphasis is placed on understanding the meandering motion of the vortices in the pair, including vortex core displacement, spectral content, stability mechanisms and overall rank-behavior. The first two energy-ranked modes obtained through Proper orthogonal decomposition (POD) of the time-resolved vorticity field reveals a pair of vortex dipoles aligned relatively perpendicularly to each other. The dynamics is successfully mapped to a matched Batchelor vortex pair whose spatial and temporal stability analyses indicate similar dipole structures associated with an |m| = 1 elliptic mode pair. This short-wave elliptic instability dominates the meandering motion, with strain due to axi...