Instabilities and sensitivities in a flow over a rotationally flexible cylinder with a rigid splitter plate
File(s)
Accepted version
Author(s)
Basso, Robin
Hwang, Yongyun
Assi, Gustavo
Sherwin, Spencer
Type
Journal Article
Abstract
This paper investigates the origin of flow-induced instabilities and their sensitivities in
a flow over a rotationally flexible circular cylinder with a rigid splitter plate. A linear
stability and sensitivity problem is formulated in the Eulerian frame by considering the
geometric nonlinearity arising from the rotational motion of the cylinder which is not
present in the stationary or purely translating stability methodology. This nonlinearity
needs careful and consistent treatment in the linearised problem particularly when
considering the Eulerian frame or reference adopted in this study and not so widely
considered. Two types of instabilities arising from the fluid-structure interaction are
found. The first type of the instabilities is the stationary symmetry-breaking mode, which
was well reported in previous studies. This instability exhibits a strong correlation with
the length of the recirculation zone. A detailed analysis of the instability mode and
its sensitivity reveals the importance of the flow near the tip region of the plate for the
generation and control of this instability mode. The second type is an oscillatory torsional
flapping mode, which has not been well reported. This instability typically emerges when
the length of the splitter plate is sufficiently long. Unlike the symmetry breaking mode,
it is not so closely correlated with the length of the recirculation zone. The sensitivity
analysis however also reveals the crucial role played by the flow near the tip region in
this instability. Finally, it is found that many physical features of this instability are
reminiscent of those of the flapping (or flutter instability) observed in a flow over a
flexible plate or a flag, suggesting that these instabilities share the same physical origin.
a flow over a rotationally flexible circular cylinder with a rigid splitter plate. A linear
stability and sensitivity problem is formulated in the Eulerian frame by considering the
geometric nonlinearity arising from the rotational motion of the cylinder which is not
present in the stationary or purely translating stability methodology. This nonlinearity
needs careful and consistent treatment in the linearised problem particularly when
considering the Eulerian frame or reference adopted in this study and not so widely
considered. Two types of instabilities arising from the fluid-structure interaction are
found. The first type of the instabilities is the stationary symmetry-breaking mode, which
was well reported in previous studies. This instability exhibits a strong correlation with
the length of the recirculation zone. A detailed analysis of the instability mode and
its sensitivity reveals the importance of the flow near the tip region of the plate for the
generation and control of this instability mode. The second type is an oscillatory torsional
flapping mode, which has not been well reported. This instability typically emerges when
the length of the splitter plate is sufficiently long. Unlike the symmetry breaking mode,
it is not so closely correlated with the length of the recirculation zone. The sensitivity
analysis however also reveals the crucial role played by the flow near the tip region in
this instability. Finally, it is found that many physical features of this instability are
reminiscent of those of the flapping (or flutter instability) observed in a flow over a
flexible plate or a flag, suggesting that these instabilities share the same physical origin.
Date Issued
2021-12-10
Date Acceptance
2021-09-06
Citation
Journal of Fluid Mechanics, 2021, 928, pp.1-32
ISSN
0022-1120
Publisher
Cambridge University Press
Start Page
1
End Page
32
Journal / Book Title
Journal of Fluid Mechanics
Volume
928
Copyright Statement
© The Author(s), 2021. Published by Cambridge University Press. This article has been published in a revised form in Journal of Fluid Mechanics https://doi.org/10.1017/jfm.2021.830. This version is free to view and download for private research and study only. Not for re-distribution, re-sale or use in derivative works.
Identifier
https://www.cambridge.org/core/journals/journal-of-fluid-mechanics/article/instabilities-and-sensitivities-in-a-flow-over-a-rotationally-flexible-cylinder-with-a-rigid-splitter-plate/FFC1B79344122ED67FCBB41C68F534FE
Subjects
01 Mathematical Sciences
09 Engineering
Fluids & Plasmas
Publication Status
Published
Date Publish Online
2021-10-06