Nonlinear optimal control of bypass transition in a boundary layer flow

Rapid path to transition via nonlinear localized optimal perturbations in a boundary-layer flow.

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 no...

Some Characteristics of Bypass Transition in a Heated Boundary Layer

Numerical studies of bypass transition in the Blasius boundary layer

Experimental findings show that transition from laminar to turbulent flow may occur also if the exponentially growing perturbations, eigensolutions to the linearised disturbance equations, are damped. An alternative non-modal growth mechanism has been recently identified, also based on the linear approximation. This consists of the transient growth of streamwise elongated disturbances, with reg...

Algebraic growth in a Blasius boundary layer: Nonlinear optimal disturbances

The three-dimensional, algebraically growing instability of a Blasius boundary layer is studied in the nonlinear regime, employing a nonparallel model based on boundary layer scalings. Adjoint-based optimization is used to determine the “optimal” steady leading-edge excitation that provides the maximum energy growth for a given initial energy. Like in the linear case, the largest transient grow...

Optimal harmonic response in a confined Bödewadt boundary layer flow.

The Bödewadt boundary layer flow on the stationary bottom end wall of a finite rotating cylinder is very sensitive to perturbations and noise. Axisymmetric radial waves propagating inward have been observed experimentally and numerically before the appearance of spiral three-dimensional instabilities. In this study, the sensitivity and response of the finite Bödewadt flow to a harmonic modulati...