Turbulent flow around convex curved tandem cylinders

Turbulent flow around curved tandem cylinders has been studied for the first time, by means of direct numerical simulation. The convex configuration was used, with a nominal gap ratio of $L/D = 3$ and a Reynolds number of 3900. Along the span, the flow regimes vary from alternating overshoot/reattac...

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Bibliographic Details
Published in:Journal of fluid mechanics 2024-10, Vol.997, Article A58
Main Authors: Aasland, Tale E., Pettersen, Bjørnar, Andersson, Helge I., Jiang, Fengjian
Format: Article
Language:English
Subjects:
Cylinders
Direct numerical simulation
Downdraft
Fluid dynamics
Fluid flow
Frequency stability
Geometry
Instability
JFM Papers
Mathematical models
Meandering
Reynolds number
Shear
Shear flow
Shear layers
Subcritical flow
Tranquil flow
Turbulent flow
Vortices
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Summary:Turbulent flow around curved tandem cylinders has been studied for the first time, by means of direct numerical simulation. The convex configuration was used, with a nominal gap ratio of $L/D = 3$ and a Reynolds number of 3900. Along the span, the flow regimes vary from alternating overshoot/reattachment to co-shedding. Three distinct Strouhal numbers coexist in the flow that are tied directly to different tandem cylinder flow regimes. This result differs substantially from convex curved tandem cylinders at a transitional Reynolds number, where only a single dominant frequency is found. All regimes exhibit some degree of instability, so that the flow can be considered multistable. A mode switch from alternating overshoot/reattachment to symmetric reattachment is found. Complex interactions are observed between the primary instability, the shear layer instability and the flow mode alterations. As opposed to previous investigations with single and tandem straight cylinders in the subcritical flow regime, our results indicate that there may be direct feedback from the primary instability to the shear layer instability. The downdraft region in the gap exhibits slow meandering, and may travel upstream and amplify the shear layer instability, causing early transition in the gap shear layer. This downdraft is governed by the slow modulations of the vortex formation region in the lower gap, meaning that the vortex dynamics of this region may indirectly influence the shear layer instability higher up in the gap.
ISSN:0022-1120
1469-7645
DOI:10.1017/jfm.2024.576