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Control of confined vortex breakdown with partial rotating lids

Mununga, Lewis and Lo Jacono, David and Sorensen, Jens N. and Leweke, Thomas and Thompson, Mark C. and Hourigan, Kerry Control of confined vortex breakdown with partial rotating lids. (2014) Journal of Fluid Mechanics, 738. 5-33. ISSN 0022-1120

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Official URL: http://dx.doi.org/10.1017/jfm.2013.596

Abstract

Experiments were conducted to determine the effectiveness of controlling vortex breakdown in a confined cylindrical vessel using a small rotating disk, which was flush-mounted into the opposite endwall to the rotating endwall driving the primary recirculating flow. The results show that the control disk, with relatively little power input, can modify the azimuthal and axial flow significantly, changing the entire flow structure in the cylinder. Co-rotation was found to precipitate vortex breakdown onset whereas counter-rotation delays it. Furthermore, for the Reynolds-number range over which breakdown normally exists, co-rotation increases the bubble radial and axial dimensions, while shifting the bubble in the upstream direction. By contrast, counter-rotation tends to reduce the size of the bubble, or completely suppress it, while shifting the bubble in the downstream direction. These effects are amplified substantially by the use of larger control disks and higher rotation ratios. A series of numerical simulations close to the onset Reynolds number reveals that the control disk acts to generate a rotation-rate-invariant local positive or negative azimuthal vorticity source away from the immediate vicinity of the control disk but upstream of breakdown. Advection of this source along streamlines modifies the strength of the azimuthal vorticity ring, which effectively controls whether the flow reverses on the axis, and thus, in turn, whether vortex breakdown occurs. The vorticity source generated by the control disk scales approximately linearly with rotation ratio and cubically with disk diameter; this allows the observed variation of the critical Reynolds number to be approximately predicted.

Item Type:Article
Additional Information:Thanks to Cambridge University Press. The definitive version is available at http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=9095357&fulltextType=RA&fileId=S002211201300596X
HAL Id:/hal-01092035
Audience (journal):International peer-reviewed journal
Uncontrolled Keywords:
Institution:Other partners > Aix-Marseille Université - AMU (FRANCE)
French research institutions > Centre National de la Recherche Scientifique - CNRS (FRANCE)
Other partners > Danmarks Tekniske Universitet - DTU (DENMARK)
Other partners > Ecole Centrale Marseille (FRANCE)
Other partners > Monash University (AUSTRALIA)
Laboratory name:
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Deposited By: David LO JACONO
Deposited On:08 Dec 2014 10:02

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