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Control of laminar separation using pulsed vortex generator jets: direct numerical simulations

Published online by Cambridge University Press:  19 April 2011

D. POSTL ,
W. BALZER  and
H. F. FASEL
D. POSTL
Affiliation:
Department of Aerospace and Mechanical Engineering, University of Arizona, Tucson, AZ 85721, USA
W. BALZER
Affiliation:
Department of Aerospace and Mechanical Engineering, University of Arizona, Tucson, AZ 85721, USA
H. F. FASEL*
Affiliation:
Department of Aerospace and Mechanical Engineering, University of Arizona, Tucson, AZ 85721, USA
*
†Email address for correspondence: faselh@email.arizona.edu
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Abstract

Direct numerical simulations (DNS) are employed to investigate laminar boundary layer separation and its control by pulsed vortex generator jets (VGJs), i.e. by injecting fluid into the flow through a spanwise array of small holes. Particular focus is directed towards identifying the relevant physical mechanisms associated with VGJ control of low-Reynolds-number separation, as encountered in low-pressure turbine applications. Pulsed VGJs are shown to be much more effective than steady VGJs when the same momentum coefficient is used for the actuation. From our investigations we have found that the increased control effectiveness of pulsed VGJs can be explained by the fact that linear hydrodynamic instability mechanisms are exploited. When pulsing with frequencies to which the separated shear layer is naturally unstable, instability modes are shown to develop into large-scale, spanwise coherent structures. These structures provide the necessary entrainment of high-momentum fluid to successfully reattach the flow.

JFM classification

Boundary Layers: Boundary layer separation Instability: Instability Flow Control: Flow Control Instability: Transition to turbulence
Type
Papers
Information
Journal of Fluid Mechanics , Volume 676 , 10 June 2011 , pp. 81 - 109
Copyright
Copyright © Cambridge University Press 2011

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Postl et al. supplementary material

Flow structures associated with pulsed vortex generator jets. Case PV-A. Side view of iso-surfaces of λ2=-5. This animation corresponds to figure 12 in the manuscript.

Download Postl et al. supplementary material(Video)
Video 1.2 MB

Postl et al. supplementary material

Flow structures associated with pulsed vortex generator jets. Case PV-A. Side view of iso-surfaces of λ2=-5. This animation corresponds to figure 12 in the manuscript.

Download Postl et al. supplementary material(Video)
Video 603.2 KB