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Title: Coherent motions in a turbulent wake of an axisymmetric bluff body

The wake flow past an axisymmetric body of revolution at a diameter-based Reynolds number$Re=u_{\infty }D/\nu =5000$is investigated via a direct numerical simulation. The study is focused on identification of coherent vortical motions and the dominant frequencies in this flow. Three dominant coherent motions are identified in the wake: the vortex shedding motion with the frequency of$St=fD/u_{\infty }=0.27$, the bubble pumping motion with$St=0.02$, and the very-low-frequency (VLF) motion originated in the very near wake of the body with the frequency$St=0.002$–$0.005$. The vortex shedding pattern is demonstrated to follow a reflectional symmetry breaking mode, whereas the vortex loops are shed alternatingly from each side of the vortex shedding plane, but are subsequently twisted and tangled, giving the resulting wake structure a helical spiraling pattern. The bubble pumping motion is confined to the recirculation region and is a result of a Görtler instability. The VLF motion is related to a stochastic destabilisation of a steady symmetric mode in the near wake and manifests itself as a slow, precessional motion of the wake barycentre. The VLF mode with$St=0.005$is also detectable in the intermediate wake and may be associated with a low-frequency radial flapping of the shear layer.

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Award ID(s):
1944568 1707075
NSF-PAR ID:
10483348
Author(s) / Creator(s):
;
Publisher / Repository:
Cambridge University Press
Date Published:
Journal Name:
Journal of Fluid Mechanics
Volume:
962
ISSN:
0022-1120
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
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