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Dynamics of laminar separation bubbles at low-Reynolds-number aerofoils

Published online by Cambridge University Press:  10 July 2009

R. HAIN ,
C. J. KÄHLER  and
R. RADESPIEL
R. HAIN
Affiliation:
Institute of Fluid Mechanics, Technische Universität Braunschweig, 38106 Braunschweig, Germany
C. J. KÄHLER*
Affiliation:
Institute of Fluid Mechanics, Technische Universität Braunschweig, 38106 Braunschweig, Germany
R. RADESPIEL
Affiliation:
Institute of Fluid Mechanics, Technische Universität Braunschweig, 38106 Braunschweig, Germany
*
†Email address for correspondence: c.kaehler@tu-bs.de
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Abstract

The laminar separation bubble on an SD7003 aerofoil at a Reynolds number Re = 66000 was investigated to determine the dominant frequencies of the transition process and the flapping of the bubble. The measurements were performed with a high-resolution time-resolved particle image velocimetry (TR-PIV) system. Contrary to typical measurements performed through conventional PIV, the different modes can be identified by applying TR-PIV. The interaction between the shed vortices is analysed, and their significance for the production of turbulence is presented. In the shear layer above the bubble the generation and amplification of vortices due to Kelvin–Helmholtz instabilities is observed. It is found that these instabilities have a weak coherence in the spanwise direction. In a later stage of transition these vortices lead to a three-dimensional breakdown to turbulence.

Type
Papers
Information
Journal of Fluid Mechanics , Volume 630 , 10 July 2009 , pp. 129 - 153
Copyright
Copyright © Cambridge University Press 2009

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