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Transverse instability and low-frequency flapping in incompressible separated boundary layer flows: an experimental study

Published online by Cambridge University Press:  13 June 2012

Pierre-Yves Passaggia ,
Thomas Leweke  and
Uwe Ehrenstein
Pierre-Yves Passaggia
Affiliation:
IRPHE, UMR 7342 CNRS, Aix–Marseille Université, F-13384 Marseille CEDEX 13, France
Thomas Leweke*
Affiliation:
IRPHE, UMR 7342 CNRS, Aix–Marseille Université, F-13384 Marseille CEDEX 13, France
Uwe Ehrenstein
Affiliation:
IRPHE, UMR 7342 CNRS, Aix–Marseille Université, F-13384 Marseille CEDEX 13, France
*
†Email address for correspondence: thomas.leweke@irphe.univ-mrs.fr
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Abstract

The unstable dynamics of a transitional laminar separation bubble behind a two-dimensional bump geometry is investigated experimentally using dye visualizations and particle image velocimetry measurements. For Reynolds numbers above a critical value, the initially two-dimensional recirculation bubble is subject to modulations in the spanwise direction which can trigger vortex shedding. Increasing the Reynolds number further, the unstable behaviour is dominated by a low-frequency flapping motion, well known in transonic flows, and here investigated for the first time experimentally in an incompressible flow regime. These phenomena are characterized by non-intrusive measurements of the spatial structure and the frequencies of the unsteady motion. The results are in excellent agreement with previous numerical and theoretical predictions for the same geometry.

JFM classification

Boundary Layers: Boundary layer separation Instability: Instability
Type
Papers
Information
Journal of Fluid Mechanics , Volume 703 , 25 July 2012 , pp. 363 - 373
Copyright
Copyright © Cambridge University Press 2012

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