{"title":"Vortex-induced vibration and flutter of a filament behind a circular cylinder","authors":"Mohd Furquan, Sanjay Mittal","doi":"10.1007/s00162-023-00644-3","DOIUrl":null,"url":null,"abstract":"<p>Flow past a flexible filament, a two-dimensional splitter plate with negligible thickness, attached behind a circular cylinder is investigated. The Reynolds number based on the free-stream speed of incoming flow and diameter of the cylinder is <span>\\(\\textrm{Re}=100\\)</span>. At this <span>\\(\\textrm{Re}\\)</span>, the flow for a rigid filament is steady. However, a flexible filament undergoes flow-induced vibration for a range of reduced speed, <span>\\(U^*\\)</span>, defined as inverse of the first nondimensionalized natural frequency of the filament. Over the wide range of <span>\\(U^*\\)</span> considered in this work (<span>\\(U^*\\le 240\\)</span>), it exhibits both flutter and vortex-induced vibration (VIV). Lock-in with various normal modes related to bending of the filament, each in a different regime of reduced speed, is observed during VIV. Interestingly, the fluid–structure system does not lock-in with the first normal mode of bending but with higher modes. The flow is steady for an extended range of reduced speed both before and after the lock-in with second mode. Two patterns of vortex shedding are observed. The <span>\\(\\textsf{2P}\\)</span> mode is associated with high-frequency vibration, while the <span>\\(\\mathsf {2\\,S}\\)</span> mode is observed during relatively low-frequency oscillation. A symmetry-breaking pitchfork bifurcation leads to static deflection of the filament during the first steady regime. The filament exhibits flutter response, at large reduced speed, with relatively low amplitude and frequency. No vortex shedding is observed during flutter. The fluid forces that cause flutter arise from asymmetry across the two sides of the filament in the zones of recirculation downstream of the cylinder. Comparison of the space-time patterns of energy transfer at the fluid–filament interface for flutter and vortex-induced vibration reveals that the energy transfer is much smaller during flutter compared to VIV. The point of maximum energy transfer is located close to the root of the filament in case of flutter, while it is near the tip during VIV.\n</p>","PeriodicalId":795,"journal":{"name":"Theoretical and Computational Fluid Dynamics","volume":"37 3","pages":"305 - 318"},"PeriodicalIF":2.2000,"publicationDate":"2023-03-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Theoretical and Computational Fluid Dynamics","FirstCategoryId":"5","ListUrlMain":"https://link.springer.com/article/10.1007/s00162-023-00644-3","RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q2","JCRName":"MECHANICS","Score":null,"Total":0}
引用次数: 0
Abstract
Flow past a flexible filament, a two-dimensional splitter plate with negligible thickness, attached behind a circular cylinder is investigated. The Reynolds number based on the free-stream speed of incoming flow and diameter of the cylinder is \(\textrm{Re}=100\). At this \(\textrm{Re}\), the flow for a rigid filament is steady. However, a flexible filament undergoes flow-induced vibration for a range of reduced speed, \(U^*\), defined as inverse of the first nondimensionalized natural frequency of the filament. Over the wide range of \(U^*\) considered in this work (\(U^*\le 240\)), it exhibits both flutter and vortex-induced vibration (VIV). Lock-in with various normal modes related to bending of the filament, each in a different regime of reduced speed, is observed during VIV. Interestingly, the fluid–structure system does not lock-in with the first normal mode of bending but with higher modes. The flow is steady for an extended range of reduced speed both before and after the lock-in with second mode. Two patterns of vortex shedding are observed. The \(\textsf{2P}\) mode is associated with high-frequency vibration, while the \(\mathsf {2\,S}\) mode is observed during relatively low-frequency oscillation. A symmetry-breaking pitchfork bifurcation leads to static deflection of the filament during the first steady regime. The filament exhibits flutter response, at large reduced speed, with relatively low amplitude and frequency. No vortex shedding is observed during flutter. The fluid forces that cause flutter arise from asymmetry across the two sides of the filament in the zones of recirculation downstream of the cylinder. Comparison of the space-time patterns of energy transfer at the fluid–filament interface for flutter and vortex-induced vibration reveals that the energy transfer is much smaller during flutter compared to VIV. The point of maximum energy transfer is located close to the root of the filament in case of flutter, while it is near the tip during VIV.
期刊介绍：
Theoretical and Computational Fluid Dynamics provides a forum for the cross fertilization of ideas, tools and techniques across all disciplines in which fluid flow plays a role. The focus is on aspects of fluid dynamics where theory and computation are used to provide insights and data upon which solid physical understanding is revealed. We seek research papers, invited review articles, brief communications, letters and comments addressing flow phenomena of relevance to aeronautical, geophysical, environmental, material, mechanical and life sciences. Papers of a purely algorithmic, experimental or engineering application nature, and papers without significant new physical insights, are outside the scope of this journal. For computational work, authors are responsible for ensuring that any artifacts of discretization and/or implementation are sufficiently controlled such that the numerical results unambiguously support the conclusions drawn. Where appropriate, and to the extent possible, such papers should either include or reference supporting documentation in the form of verification and validation studies.
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