Absolute equilibrium dynamics in 3d turbulence
Turbulence is ubiquitous in atmospheric winds, ocean currents, and industrial flows and presents complex out-of-equilibrium dynamics, characterized by a wide range of interacting length scales. Experimental and numerical studies of three-dimensional turbulence are generally designed to inject energy at scales comparable to the system size to capture how the energy cascades in the inertial range. Yet, many geophysical or astrophysical flows involve spatial scales larger than the forcing scale, whose dynamics are well described by non-dissipative Euler equations and therefore differ fundamentally from the cascade regime. This naturally raises the question of whether the large scales of 3D turbulence behave as an out-of-equilibrium system or as an equilibrium isolated system.
To directly probe the large-scale dynamics of 3D turbulent flow, we will introduce a new experimental setup with a clear separation between the forcing scale and the system size. We will demonstrate that the generated flow satisfies the assumptions of Kolmogorov theory, and show experimentally for the first time that the large scales of 3D turbulence thermalize, indicating an absolute equilibrium regime. We will also quantify the temporal decay to establish a direct link between the large-scale Saffman invariants and the energy spectrum. Our results provide a new framework to describe turbulent flows using concepts of statistical mechanics.
Contact Nathanaël Machicoane for more information or to schedule a discussion with the seminar speaker.