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The role of separation on the forces acting on a circular cylinder with a control rod

Published online by Cambridge University Press:  11 March 2021

M.M. Cicolin Open the ORCID record for M.M. Cicolin [Opens in a new window] ,
O.R.H. Buxton Open the ORCID record for O.R.H. Buxton [Opens in a new window] ,
G.R.S. Assi Open the ORCID record for G.R.S. Assi [Opens in a new window]  and
P.W. Bearman
M.M. Cicolin*
Affiliation:
Department of Aeronautics, Imperial College London, LondonSW7 2AZ, UK Escola Politécnica, University of São Paulo, Brazil
O.R.H. Buxton
Affiliation:
Department of Aeronautics, Imperial College London, LondonSW7 2AZ, UK
G.R.S. Assi
Affiliation:
Escola Politécnica, University of São Paulo, Brazil
P.W. Bearman
Affiliation:
Department of Aeronautics, Imperial College London, LondonSW7 2AZ, UK
*
†Email address for correspondence: [email protected]
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Abstract

The development of the flow around a circular cylinder with a smaller diameter control rod in close proximity is the subject of this paper. It has long been known that this is an effective way to attenuate regular vortex shedding leading to reductions in its adverse effects on bluff-body flow. The aim of this study is to improve understanding of the ways the control rod affects the near-wake flow including how it influences the positions of boundary layer separation. Experiments were carried out in a water channel to measure lift and drag forces and particle image velocimetry (PIV) was employed to obtain detailed information on flow structure. The values of important properties were fixed as follows: Reynolds number, 20 000; ratio of cylinder and control rod diameters, 10 : 1; centre-to-centre distance between main cylinder and control rod, 0.7$D$ (where $D$ is the main cylinder diameter). The adjustable parameter was the angular position of the rod, $\theta$, which was varied between $90^{\circ }$ and $180^{\circ }$ from the front stagnation line. Lift and drag forces were measured separately for the main cylinder and the control rod. A new method for identifying flow states is introduced using PIV to interrogate the instantaneous flow velocity in the gap between the main cylinder and the control rod. Similarly to previous studies, three stable flow states were observed together with a bistable state. The bistable state is very sensitive to the control rod angle with a small change of ${\pm }1^{\circ }$ being sufficient to change the flow state.

JFM classification

Wakes/Jets: Vortex streets Vortex Flows: Vortex shedding
Type
JFM Papers
Information
Journal of Fluid Mechanics , Volume 915 , 25 May 2021 , A33
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Copyright
© The Author(s), 2021. Published by Cambridge University Press

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References

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Cicolin et al. supplementary movie 1

Vortex street past a bare cylinder at Re=20 000.

Download Cicolin et al. supplementary movie 1(Video)
Video 2 MB

Cicolin et al. supplementary movie 2

Typical wake of state I. case θ=90°

Download Cicolin et al. supplementary movie 2(Video)
Video 1.9 MB

Cicolin et al. supplementary movie 3

Typical wake of state II. case θ=120°

Download Cicolin et al. supplementary movie 3(Video)
Video 2 MB

Cicolin et al. supplementary movie 4

Typical wake of state III. case θ=135°

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Video 2 MB

Cicolin et al. supplementary movie 5

Bi-stable case, θ=130°

Download Cicolin et al. supplementary movie 5(Video)
Video 7.9 MB