Stable state of mode A for flow past a circular cylinder

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Abstract

A stable three-dimensional (3D) wake structure for flow past a circular cylinder has been discovered through 3D direct numerical simulations (DNS). The stable 3D wake structure occurs over a small range of Reynolds number (Re) below the critical Re for Mode A* (i.e., Mode A with large-scale vortex dislocations, where Mode A is the first 3D instability mode which will evolve into Mode A*) instability. It is believed that the stable 3D wake structure discovered in this study is the stable state of Mode A wake structure inferred by Williamson ["Three-dimensional wake transition," J. Fluid Mech. 328, 345-407 (1996)]. This confirms the wake transition sequence of 2D → A → A* → B suggested byWilliamson. Compared with conventional Mode A structure, the stable state of Mode A structure has much weaker amplitude and does not evolve into large-scale vortex dislocations. The stable state of Mode A structure is triggered by small-scale spanwise disturbance introduced upstream of the cylinder, due to energy amplification through convective instability of the flow. The stable state of Mode A is transient and is damped out eventually under a transient initial disturbance condition, but is sustained throughout under a persistent disturbance condition. The emergence of the stable state of Mode A structure is correlated with both Re and the disturbance level. With the decrease of Re, the stable state of Mode A structure gradually becomes less well-defined and eventually disappears. With the decrease of the disturbance level, the stable state of Mode A structure emerges at a higher Re.

Original languageEnglish
Article number104103
Pages (from-to)104103-1 to 104103-13
Number of pages13
JournalPhysics of Fluids
Volume28
Issue number10
DOIs
Publication statusPublished - 1 Oct 2016

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circular cylinders
wakes
disturbances
vortices
direct numerical simulation
upstream
Reynolds number

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title = "Stable state of mode A for flow past a circular cylinder",
abstract = "A stable three-dimensional (3D) wake structure for flow past a circular cylinder has been discovered through 3D direct numerical simulations (DNS). The stable 3D wake structure occurs over a small range of Reynolds number (Re) below the critical Re for Mode A* (i.e., Mode A with large-scale vortex dislocations, where Mode A is the first 3D instability mode which will evolve into Mode A*) instability. It is believed that the stable 3D wake structure discovered in this study is the stable state of Mode A wake structure inferred by Williamson [{"}Three-dimensional wake transition,{"} J. Fluid Mech. 328, 345-407 (1996)]. This confirms the wake transition sequence of 2D → A → A* → B suggested byWilliamson. Compared with conventional Mode A structure, the stable state of Mode A structure has much weaker amplitude and does not evolve into large-scale vortex dislocations. The stable state of Mode A structure is triggered by small-scale spanwise disturbance introduced upstream of the cylinder, due to energy amplification through convective instability of the flow. The stable state of Mode A is transient and is damped out eventually under a transient initial disturbance condition, but is sustained throughout under a persistent disturbance condition. The emergence of the stable state of Mode A structure is correlated with both Re and the disturbance level. With the decrease of Re, the stable state of Mode A structure gradually becomes less well-defined and eventually disappears. With the decrease of the disturbance level, the stable state of Mode A structure emerges at a higher Re.",
author = "Hongyi Jiang and Liang Cheng and Feifei Tong and Scott Draper and Hongwei An",
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Stable state of mode A for flow past a circular cylinder. / Jiang, Hongyi; Cheng, Liang; Tong, Feifei; Draper, Scott; An, Hongwei.

In: Physics of Fluids, Vol. 28, No. 10, 104103, 01.10.2016, p. 104103-1 to 104103-13.

Research output: Contribution to journalArticle

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