A dynamical mechanism for turbulence self-replication in transitional flows
Lundi 27/06/2022, 14:00-15:00
A dynamical understanding of the transition to turbulence in wall bounded flows has been elusive for over a century. Based on a growing set of data, the transition is expected to be an out of-equilibrium phase transition, lying in the directed percolation universality class. The key objects in this picture are localized turbulent structures, called puffs in pipe-flow, which coexist with laminar flow and whose decay and self-replication induce the transition. The dynamical mechanism underlying puff decay is relatively well understood; I will present the first-ever comparable mechanism for puff self-replication. This mechanism provides a first understanding of how an alternative to the directed percolation picture could arise. I will motivate our claims on general grounds and will demonstrate them within a phenomenological model proposed by D. Barkley---a model which remarkably captures the essence of the transitional regime, as previously shown.
Finally, I will show that the proposed mechanism implies the existence of an “anti-puff” state, a mirror image of the puff, as well as other novel states. I will explain how these states are a part of a unified picture for the phase space of transitional pipe flow.