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Low-dimensional dynamics of a turbulent axisymmetric wake

Published online by Cambridge University Press:  14 August 2014

G. Rigas ,
A. R. Oxlade ,
A. S. Morgans  and
J. F. Morrison
G. Rigas*
Affiliation:
Department of Aeronautics, Imperial College London, London SW7 2AZ, UK
A. R. Oxlade
Affiliation:
Department of Aeronautics, Imperial College London, London SW7 2AZ, UK
A. S. Morgans
Affiliation:
Department of Aeronautics, Imperial College London, London SW7 2AZ, UK
J. F. Morrison
Affiliation:
Department of Aeronautics, Imperial College London, London SW7 2AZ, UK
*
†Email address for correspondence: g.rigas@imperial.ac.uk
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Abstract

The coherent structures of a turbulent wake generated behind a bluff three-dimensional axisymmetric body are investigated experimentally at a diameter-based Reynolds number of $\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}{\sim }2\times 10^5$. Proper orthogonal decomposition of base pressure measurements indicates that the most energetic coherent structures retain the structure of the symmetry-breaking laminar instabilities and are manifested as unsteady vortex shedding with azimuthal wavenumber $m={\pm }1$. In a rotating reference frame, the shedding preserves the reflectional symmetry and is linked with a reflectionally symmetric mean pressure distribution on the base. Due to a slow rotation of the symmetry plane of the turbulent wake around the axis of the body, statistical axisymmetry is recovered in the time average. The ratio of the time scales associated with the slow rotation of the symmetry plane and the vortex shedding is of order 100.

JFM classification

Turbulent Flows: Turbulent Flows Vortex Flows: Vortex shedding Wakes/Jets: Wakes/Jets

Information

Type
Rapids
Information
Journal of Fluid Mechanics , Volume 755 , 25 September 2014 , R5
Copyright
© 2014 Cambridge University Press 

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