Weak nonlinearity for strong non-normality

François GALLAIRE

EPFL, Lausanne


In this work with Y.-M. Ducimetière and E. Boujo, we propose a theoretical approach to derive amplitude equations governing the weakly nonlinear evolution of nonnormal dynamical systems when they experience transient growth or respond to harmonic forcing. This approach reconciles the nonmodal nature of these growth mechanisms and the need for a center manifold to project the leading-order dynamics. Under the hypothesis of strong nonnormality, we take advantage of the fact that small operator perturbations suffice to make the inverse resolvent and the inverse propagator singular, which we encompass in a multiple-scale asymptotic expansion. The methodology is outlined for a generic nonlinear dynamical system, and several application cases which highlight common nonnormal mechanisms in hydrodynamics: the streamwise convective nonnormal amplification in the flow past a backward-facing step, and the Orr and lift-up mechanisms in the plane Poiseuille flow.


                                                                                                                                                                                                                                               

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Formation d'une circulation grande échelle (plus de détails...)

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CONFÉRENCES

Auto-organisation en physique et en biologie, morphogenèse, ondes-particules, turbulence, physique non linéaire, Colloque International en mémoire d’Yves Couder à l'ENS et UPCité, 4 Juin 2024

Bifurcations and Instabilities in Fluid Dynamics, Edinburgh, Scotland, 24 Juin 2024

1st European Fluid Dynamics Conference - EFDC 2024, Aachen, Germany, 16 Septembre 2024

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