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Published (Version of record)CC BY V4.0, Open Access
Published (Version of record)CC BY V4.0, Open
Journal article
Three-dimensional wake transitions of steady flow past two side-by-side cylinders
Journal of fluid mechanics, Vol.972, A17
10/10/2023
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Abstract
Three-dimensional (3-D) wake transitions of a steady flow past two side-by-side circular cylinders are investigated through Floquet analysis and direct numerical simulations (DNS) over the gap-to-diameter ratio $g^*$ up to 3.5 and Reynolds number ${\textit {Re}}$ up to 400. When the flows behind two cylinders form in-phase and anti-phase wakes at large $g^*$, the wake transition is similar to the isolated cylinder counterpart, with the critical ${\textit {Re}}$ for the onset of 3-D transition (${\textit {Re}}_{cr-1}$) happens at around 180. At small $g^*$, 3-D transition becomes interestingly complex due to the distinct characteristics formed in base flows. The ${\textit {Re}}_{cr-1}$ suddenly drops to around 60–100 and forms distinct variation trends with $g^*$. Precisely, the ${\textit {Re}}_{cr-1}$ of the single symmetric wake (SS, $g^*\lessapprox 0.25$) is more than half of the isolated cylinder counterpart due to the large length scale of the SS wake. Only mode A is detected in SS. In the asymmetric single wake (ASS, $g^* \approx 0.25\unicode{x2013}0.6$) and flip-flop wake (FF, $g^* \approx 0.6\unicode{x2013}1.8$), the 3-D transition develops at ${\textit {Re}} \approx 103\unicode{x2013}60$ and 75–60, respectively. The decrease in ${\textit {Re}}_{cr-1}$ with increasing $g^*$ is because of the increased level of wake asymmetry in ASS and irregular vortex shedding in FF. Floquet analysis predicts two new unstable modes, namely mode A$'$ and subharmonic mode C$'$, of ASS. Both modes are transient features in 3-D DNS and the flow eventually saturates into a new 3-D mode, mode ASS. The gap flow of mode ASS is distinctly characterised by its time-independent spanwise waviness structure that is deflected towards different transverse directions with a long wavelength of about $14$ cylinder diameters. The 3-D mode of the FF is irregular both temporally and spatially. Variations of ${\textit {Re}}_{cr-1}$ with $g^*$, the characteristics and the physical mechanisms of each 3-D mode are discussed in this study.
Details
- Title
- Three-dimensional wake transitions of steady flow past two side-by-side cylinders
- Creators
- Chengjiao Ren - University of Western AustraliaZinan Liu - South China University of TechnologyLiang Cheng - University of Western AustraliaFeifei Tong - Southern Cross UniversityChengwang Xiong - Harbin Engineering University
- Publication Details
- Journal of fluid mechanics, Vol.972, A17
- Publisher
- Cambridge University Press
- Number of pages
- 38
- Identifiers
- 991013141779702368
- Copyright
- © The Author(s), 2023. Published by Cambridge University Press. This is an Open Access article, distributed under the terms of the Creative Commons Attribution licence (http://creativecommons.org/licenses/by/4.0).
- Academic Unit
- Faculty of Science and Engineering; Engineering
- Language
- English
- Resource Type
- Journal article