Orateur
Description
Subcritical shear flows are characterised by the competition between two different attractors, namely the laminar and the turbulent regimes. The concept of “lower” edge manifold refers to the basin boundary in state space, separating initial conditions which
relaminarise from those which become turbulent. It has become central in the study of transition to turbulence. Recent studies have also introduced the notion of an ‘upper
edge’ relevant to control strategies. This manifold separates turbulent trajectories from higher energy initial conditions that relaminarise, thus mediating transition from turbulent to laminar. It stands in contrast to the well-studied
‘lower edge’ that separates initial conditions which have enough energy to become turbulent from
those that do not. In this study, we focus numerically on cylindrical pipe flow, and we adapt the bisection algorithm to the upper edge. We will explore the theoretical connections between these two concepts. In a second part we will discuss computational
optimisation methods for the identification of the weakest perturbations able to force a turbulent flow to relaminarise.