Transient growth of coherent streaks for control of turbulent flow separation
by G. Pujals, S. Depardon, C. Cossu
International Journal of Aerodynamics (IJAD), Vol. 1, No. 3/4, 2011

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.

Online publication date: Sat, 28-Feb-2015

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