title: Rapid path to transition via nonlinear localized optimal perturbations in a boundary-layer flow.
abstract: Recent studies have suggested that in some cases transition can be triggered by some purely nonlinear mechanisms. Here we aim at verifying such an hypothesis, looking for a localized perturbation able to lead a boundary-layer flow to a chaotic state, following a nonlinear route. Nonlinear optimal localized perturbations have been computed by means of an energy optimization which includes the nonlinear terms of the Navier-Stokes equations. Such perturbations lie on the turbulent side of the laminar-turbulent boundary, whereas, for the same value of the initial energy, their linear counterparts do not. The evolution of these perturbations toward a turbulent flow involves the presence of streamwise-inclined vortices at short times and of hairpin structures prior to breakdown.
authors.affiliation: DIMeG and CEMeC, Politecnico di Bari, Bari, Italy. s.cherubini@gmail.com
authors.forename: S
authors.initials: S
authors.lastname: Cherubini
authors.forename: P
authors.initials: P
authors.lastname: De Palma
authors.forename: J-Ch
authors.initials: JC
authors.lastname: Robinet
authors.forename: A
authors.initials: A
authors.lastname: Bottaro