Journal of Fluid Mechanics


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

R. HAINa1 p1, C. J. KÄHLERa1 p1 c1 and R. RADESPIELa1

a1 Institute of Fluid Mechanics, Technische Universität Braunschweig, 38106 Braunschweig, Germany


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.

(Received November 23 2007)

(Revised February 16 2009)


c1 Email address for correspondence:

p1 Present address: Institute of Fluid Mechanics and Aerodynamics, Bundeswehr University Munich, 85577 Neubiberg, Germany.