Rare Events in Fluid Turbulence: Coherent Structures and Turbulence Induced Transitions
Tobias Grafke (University of Warwick, UK)
Fluid in its turbulent state is one of the most complex interacting systems in physics, with an incredibly large number of strongly and nonlinearly interacting degrees of freedom. This becomes different when scale separation introduces coherent, long-lived structures into the fluid flow, which induces order and stability. I will present three very different scenarios of that type: (1) atmospheric jets on gas giants sustained by the turbulent background fluctuations, (2) turbulent puffs at the onset of turbulence in pipe flows, and (3) metastability of Earth's climate on very long timescales. In these systems, the coherent structures might exist in a multitude of metastable configurations, and turbulent fluctuations drives transitions between them. I will analyze these metastable states, their basins of attraction, separating hypersurfaces, transition states and most likely transition trajectories from the perspective of bifurcation theory, stochastic averaging, and large deviation theory.