ECOLE DOCTORALE
« Mécanique, Energétique, Génie Civil, Procédés »
Vous êtes cordialement invités à la soutenance de la thèse de
Gerardo Del Guercio
7 novembre 2014, 10h
Amphitheatre Nougaro, Insitute de mecanique des Fluides de Toulouse
Optimal streaks amplification in wakes and vortex shedding control
Résumé
We compute optimal energy growths leading to streamwise streaks
in parallel, weakly non-parallel and the circular cylinder wakes.
We find that very large energy amplifications can be sustained by
these wakes. The energy amplifications increase with the spanwise
wavelength of the perturbations except in the circular cylinder
wake where maximum energy growths are reached for λz ≈ 5-7 D.
The optimally amplified structures are streamwise streaks. When
forced with finite amplitudes these streaks are shown, in
parallel wakes, to be able to completely suppress the absolute
instability. The global instability of the weakly non-parallel
and the circular cylinder wakes can be completely suppressed with
moderate streaks amplitudes. The energy required to stabilize the
wake is much reduced when optimal perturbations are used, and it
is shown to be always smaller than the one that would be required
if a 2D control was used. It is also shown that the
sensitivity of the global mode growth rate is quadratic and that
therefore usual first order sensitivity analyses are unable to
predict the high efficiency of the control-by-streaks strategy. Some preliminary results
from an experimental investigations of streaks forcing in the turbulent wake of a 3D
body are also shown in the last section.
Mots-Clés: streaks, flow control, local/global instabilities, wakes
Etablissement d’inscription : INP Institut National Polytechnique de Toulouse
Composition du Jury:
Prénom, Nom, titre des membres du jury
M. Pierre Brancher, Examinateur, IMFT - Toulouse
M. Olivier Cadot, Rapporteur, UME - ENSTA - Palaiseau
M. Carlo Cossu, Director de these, IMFT – Toulouse
M. Benoit Pier, Examinateur, LMFA, Ecole Centrale, Lyon
M. Gregory Pujals, Tuteur industriel, PSA Peugeot Citroen, Velizy
M. Jean-Christophe Robinet, Rapporteur, DynFluid - Arts et Metiers - Paris