The influence of a small upstream wire on transition in a rotating cylinder wake

Anirudh Narayan Rao, Alexander Radi, Justin Scott Leontini, Mark Christopher Thompson, John Sheridan, Kerry Hourigan

Research output: Contribution to journalArticleResearchpeer-review

Abstract

Recent experimental research on rotating cylinder wakes has found that a previously numerically predicted subharmonic instability mode, mode C, occurs for considerably lower rotation rates than predicted through stability analysis, yet other mode transitions occur closer to the predicted onset. One difference between the theoretical and experimental set-ups is the use of a small-diameter hydrogen bubble visualisation wire placed upstream of the rotating cylinder. The current paper tests the hypothesis that a wire, of only 1/100th of the cylinder diameter, placed five diameters upstream of the cylinder, sufficiently perturbs the flow to substantially affect certain wake transitions, including the onset of mode C. This is achieved using stability analysis of a flow that includes the upstream wire. The results indeed show that the wire of a tiny diameter induces a non-negligible asymmetry in the flow, triggering the subharmonic mode at substantially lower rotation rates. Furthermore, at higher rotation rates, the onset of two other three-dimensional modes are delayed to higher Reynolds numbers. These results make the point that even seemingly minute perturbations caused by minimally intrusive methods may result in substantially altered experimental flow behaviour.
Original languageEnglish
Pages (from-to)1 - 12
Number of pages12
JournalJournal of Fluid Mechanics
Volume769
DOIs
Publication statusPublished - Apr 2015

Keywords

  • Instability
  • Parametric instability
  • Wakes

Cite this

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title = "The influence of a small upstream wire on transition in a rotating cylinder wake",
abstract = "Recent experimental research on rotating cylinder wakes has found that a previously numerically predicted subharmonic instability mode, mode C, occurs for considerably lower rotation rates than predicted through stability analysis, yet other mode transitions occur closer to the predicted onset. One difference between the theoretical and experimental set-ups is the use of a small-diameter hydrogen bubble visualisation wire placed upstream of the rotating cylinder. The current paper tests the hypothesis that a wire, of only 1/100th of the cylinder diameter, placed five diameters upstream of the cylinder, sufficiently perturbs the flow to substantially affect certain wake transitions, including the onset of mode C. This is achieved using stability analysis of a flow that includes the upstream wire. The results indeed show that the wire of a tiny diameter induces a non-negligible asymmetry in the flow, triggering the subharmonic mode at substantially lower rotation rates. Furthermore, at higher rotation rates, the onset of two other three-dimensional modes are delayed to higher Reynolds numbers. These results make the point that even seemingly minute perturbations caused by minimally intrusive methods may result in substantially altered experimental flow behaviour.",
keywords = "Instability, Parametric instability, Wakes",
author = "Rao, {Anirudh Narayan} and Alexander Radi and Leontini, {Justin Scott} and Thompson, {Mark Christopher} and John Sheridan and Kerry Hourigan",
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language = "English",
volume = "769",
pages = "1 -- 12",
journal = "Journal of Fluid Mechanics",
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The influence of a small upstream wire on transition in a rotating cylinder wake. / Rao, Anirudh Narayan; Radi, Alexander; Leontini, Justin Scott; Thompson, Mark Christopher; Sheridan, John; Hourigan, Kerry.

In: Journal of Fluid Mechanics, Vol. 769, 04.2015, p. 1 - 12.

Research output: Contribution to journalArticleResearchpeer-review

TY - JOUR

T1 - The influence of a small upstream wire on transition in a rotating cylinder wake

AU - Rao, Anirudh Narayan

AU - Radi, Alexander

AU - Leontini, Justin Scott

AU - Thompson, Mark Christopher

AU - Sheridan, John

AU - Hourigan, Kerry

PY - 2015/4

Y1 - 2015/4

N2 - Recent experimental research on rotating cylinder wakes has found that a previously numerically predicted subharmonic instability mode, mode C, occurs for considerably lower rotation rates than predicted through stability analysis, yet other mode transitions occur closer to the predicted onset. One difference between the theoretical and experimental set-ups is the use of a small-diameter hydrogen bubble visualisation wire placed upstream of the rotating cylinder. The current paper tests the hypothesis that a wire, of only 1/100th of the cylinder diameter, placed five diameters upstream of the cylinder, sufficiently perturbs the flow to substantially affect certain wake transitions, including the onset of mode C. This is achieved using stability analysis of a flow that includes the upstream wire. The results indeed show that the wire of a tiny diameter induces a non-negligible asymmetry in the flow, triggering the subharmonic mode at substantially lower rotation rates. Furthermore, at higher rotation rates, the onset of two other three-dimensional modes are delayed to higher Reynolds numbers. These results make the point that even seemingly minute perturbations caused by minimally intrusive methods may result in substantially altered experimental flow behaviour.

AB - Recent experimental research on rotating cylinder wakes has found that a previously numerically predicted subharmonic instability mode, mode C, occurs for considerably lower rotation rates than predicted through stability analysis, yet other mode transitions occur closer to the predicted onset. One difference between the theoretical and experimental set-ups is the use of a small-diameter hydrogen bubble visualisation wire placed upstream of the rotating cylinder. The current paper tests the hypothesis that a wire, of only 1/100th of the cylinder diameter, placed five diameters upstream of the cylinder, sufficiently perturbs the flow to substantially affect certain wake transitions, including the onset of mode C. This is achieved using stability analysis of a flow that includes the upstream wire. The results indeed show that the wire of a tiny diameter induces a non-negligible asymmetry in the flow, triggering the subharmonic mode at substantially lower rotation rates. Furthermore, at higher rotation rates, the onset of two other three-dimensional modes are delayed to higher Reynolds numbers. These results make the point that even seemingly minute perturbations caused by minimally intrusive methods may result in substantially altered experimental flow behaviour.

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KW - Parametric instability

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