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Bending oscillations of a cylinder freely falling in still fluid

Published online by Cambridge University Press:  04 November 2020

Patricia Ern Open the ORCID record for Patricia Ern [Opens in a new window] ,
Jérôme Mougel Open the ORCID record for Jérôme Mougel [Opens in a new window] ,
Sébastien Cazin Open the ORCID record for Sébastien Cazin [Opens in a new window] ,
Manuel Lorite-Díez Open the ORCID record for Manuel Lorite-Díez [Opens in a new window]  and
Rémi Bourguet Open the ORCID record for Rémi Bourguet [Opens in a new window]
Patricia Ern*
Affiliation:
Institut de Mécanique des Fluides de Toulouse (IMFT), CNRS, Université de Toulouse, France
Jérôme Mougel
Affiliation:
Institut de Mécanique des Fluides de Toulouse (IMFT), CNRS, Université de Toulouse, France
Sébastien Cazin
Affiliation:
Institut de Mécanique des Fluides de Toulouse (IMFT), CNRS, Université de Toulouse, France
Manuel Lorite-Díez
Affiliation:
Institut de Mécanique des Fluides de Toulouse (IMFT), CNRS, Université de Toulouse, France
Rémi Bourguet
Affiliation:
Institut de Mécanique des Fluides de Toulouse (IMFT), CNRS, Université de Toulouse, France
*
†Email address for correspondence: [email protected]
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Abstract

We investigate experimentally the behaviour of an elongated flexible cylinder settling at moderate Reynolds number under the effect of buoyancy in a fluid otherwise at rest. The experiments uncover the development of large-amplitude periodic deformations of the cylinder (of the order of its diameter) in specific parameter ranges. Bending oscillations are observed to occur for two base flow situations, involving either a steady or an unsteady wake. In both cases, the sequence of oscillatory deformations emerging when the cylinder length is increased involves the bending modes of an unsupported cylinder with free ends. Comparison of the deformation frequency measured for the falling cylinder with the vortex shedding frequency expected for a non-deformable cylinder at the same Reynolds number indicates that the deformation is coupled to the wake unsteadiness. It also suggests that the cylinder degrees of freedom in deformability allow wake instability to be triggered at Reynolds numbers that would be subcritical for fixed rigid cylinders.

JFM classification

Wakes/Jets: Wakes
Type
JFM Rapids
Information
Journal of Fluid Mechanics , Volume 905 , 25 December 2020 , R5
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Copyright
© The Author(s), 2020. Published by Cambridge University Press

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References

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