Critical Reynolds number and galloping instabilities – Experiments on circular cylinders

Nikolaos Nikitas, John H G Macdonald, JB Jakobsen, TL Andersen

Research output: Contribution to journalArticle (Academic Journal)peer-review

33 Citations (Scopus)

Abstract

The current paper considers large galloping-like vibrations of circular cylinders, generically inclined and yawed to the flow. The case of a round section prone to galloping is seemingly a paradox since rotational symmetry (or close to it) and classical galloping are apparently contradictory. Still there seems to be a range of wind speeds far from those for typical Kármán vortex shedding resonance where such a phenomenon does occur. Experimental results from both static and dynamic large-scale rigid cable models, presented here, show that this range coincides with the critical Reynolds number regime, where notable symmetry-breaking characteristics such as nonzero mean lift emerge. It is shown that a fundamental difference between the inclined and non-inclined cylinder aerodynamics may exist accommodating different pressure distributions and different resulting dynamic behaviours. Unsteady pressure measurements showing avalanche-like “jumps” and vortex dislocations building between cell structures in the cylinder spanwise direction are conjectured to be a key element in the unstable behaviour experienced.
Original languageEnglish
Pages (from-to)1295-1306
JournalExperiments in Fluids
Volume52
Issue number5
Early online date31 Dec 2011
DOIs
Publication statusPublished - May 2012

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