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Local and global instabilities in the wake of a sphere

Published online by Cambridge University Press:  30 April 2008

BENOÎT PIER*
Affiliation:
Laboratoire de mécanique des fluides et d'acoustique, École centrale de Lyon, CNRS, Université Claude-Bernard Lyon 1, INSA Lyon, 36 avenue Guy-de-Collongue, 69134 Écully cedex, France

Abstract

The global dynamics of open shear flows is closely related to the nature of their local instability characteristics, either convective or absolute. The present investigation revisits the wake of a sphere, obtains its global behaviour by direct numerical simulations and derives its local stability features, computed for the underlying basic flow under a quasi-parallel flow assumption. It is shown that both the axisymmetric and the planar symmetric basic flows exhibit domains of local absolute instability in the near-wake region. The largest absolute growth rates occur for instabilities developing on the non-axisymmetric basic wake and conserving its planar symmetry.

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Type
Papers
Copyright
Copyright © Cambridge University Press 2008

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