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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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The dynamics of coherent structures in a turbulent wake past a sphere at Re= 3700
The turbulent wake flow past a sphere at ReD= 3700 is investigated via Direct Numerical Simulation (DNS). The characteristic motions in the wake flow, such as vortex shedding and bubble pumping are identified by the probes placed in the near wake with a dominating frequency of St= fu∞/D= 0.22 and 0.004, respectively. The modal analysis is conducted in the wake area using Proper Orthogonal Decomposition (POD) and Dynamic Mode Decomposition (DMD). The vortex shedding and bubble pumping motions are also captured by the modal analysis. The results from POD and DMD show comparable patterns of both characteristic motions. For the bubble pumping motion, the dominating frequency of the corresponding POD mode is St= 0.004, while the DMD mode that is directly related to the separation bubble has the frequency of St= 0.009.
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- PAR ID:
- 10388151
- Publisher / Repository:
- Twelfth International Symposium on Turbulence and Shear Flow Phenomena
- Date Published:
- Journal Name:
- Turbulence and shear flow phenomena
- Volume:
- 2022
- ISSN:
- 2642-0554
- Page Range / eLocation ID:
- 246
- Format(s):
- Medium: X
- Location:
- Osaka, Japan
- Sponsoring Org:
- National Science Foundation
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