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SUMMARY:Lift-up and convective nonnormalities : the dynamics of a recircul
 ation bubble - Chomaz\, JM (CBRS-Ecole Polytechnique)
DTSTART:20080912T103000Z
DTEND:20080912T105000Z
UID:TALK13389@talks.cam.ac.uk
CONTACT:Mustapha Amrani
DESCRIPTION:The stability of the recirculation bubble behind a smoothed ba
 ckward-facing step is numerically computed. Destabilization occurs through
  a stationary three-dimensional mode. Analysis of the direct global mode s
 hows that the instability corresponds to a deformation of the recirculatio
 n bubble in which streamwise vortices induce low and high speed streaks as
  in the classical lift-up mechanism. Formulation of the adjoint problem an
 d computation of the adjoint global mode show that both the lift-up mechan
 ism associated to the transport of the base flow by the perturbation and t
 he convective nonnormality associated to the transport of the perturbation
  by the base flow explain the properties of the flow. The lift-up nonnorma
 lity differentiates the direct and adjoint modes by their component: the d
 irect is dominated by the streamwise component and the adjoint by the cros
 s-stream component. The convective nonnormality results in a different loc
 alization of the direct and adjoint global modes\, respectively downstream
  and upstream. Implication of these properties on the linear and nonlinear
  dynamics will be discussed. \n\nco-workers: O. MARQUET\, M. LOMBARDI \, D
 . SIPP AND L. JACQUIN Departement d'Aerodynamique Fondamentale et Experime
 ntale\, ONERA\, 92190 Meudon\, France 
LOCATION:Seminar Room 1\, Newton Institute
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