Title: Transient growth of coherent streaks for control of turbulent flow separation

Authors: G. Pujals, S. Depardon, C. Cossu

Addresses: LadHyX, CNRS-Ecole Polytechnique, F-91128 Palaiseau, France; PSA Peugeot Citroen, Centre Technique de Velizy, 2 Route de Gisy, 78943 Velizy-Villacoublay Cedex, France. ' PSA Peugeot Citroen, Centre Technique de Velizy, 2 Route de Gisy, 78943 Velizy-Villacoublay Cedex, France. ' IMFT-CNRS, Allee du Pr. Camille Soula, 31400 Toulouse, France

Abstract: In this paper, we summarise our recent results on turbulent flow separation control using transient growth of large-scale coherent streaks. According to linear stability analysis, the optimal perturbations (i.e., disturbances experiencing the largest transient energy growth) sustained by a turbulent boundary layer are large-scale streamwise uniform coherent vortices leading to streaks, the lift-up effect being responsible for their growth. A first experimental study confirms that using arrays of suitably shaped cylindrical roughness elements, streaks can be artificially forced in a flat plate turbulent boundary layer at a Reynolds number based on the displacement thickness of 1,000. Interacting with the mean flow at leading order, these streaks induce a strong controlled spanwise modification and that their amplitude transiently grows in space. Eventually, streaks are forced on the roof of a generic car model (Ahmed body, see Ahmed et al., 1984) to test their ability to suppress the separation around the rear-end.

Keywords: turbulent boundary layers; streaks; transient growth; turbulent flow; flow separation; separation control; Ahmed body; automotive aerodynamics.

DOI: 10.1504/IJAD.2011.038848

International Journal of Aerodynamics, 2011 Vol.1 No.3/4, pp.318 - 336

Available online: 04 Mar 2011 *

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