The TRR 181 seminar is held by Dr. Alberto Vela Martín (University Bremen) ) on June 2, 11 am.

Non-equilibrium, fluxes and coherence: new perspectives in our understanding of the turbulence energy cascade

Abstract

The energy cascade is perhaps one of the most successful paradigms in turbulence.The ideas originally proposed by Richardson, Kolmogorov or Obukhov, among others, have crystallized over decades of research in a consistent picture of turbulence at high Reynolds numbers:energy is injected at the large scales and transported in scale through the inertial range until dissipation becomes effective in the small scales, even for vanishing kinematic viscosity. Many properties of this process have been extensively studied,yet the energy cascade is far from fully understood. 

In this talk we will discuss new aspects of the energy cascade that have emerged recently thanks to high-quality numerical data. It will be shown how cascades can be understood in the framework of statistical mechanics: they naturally emerge from non-equilibrium ensembles, and the direction of their fluxes can be predicted by equilibrium thermodynamics. Non-equilibrium leads to an almost unidirectional coupling from large to small scales which has practical and theoretical consequences. First, we will see that the energy cascade can be modeled as a purely dissipative and irreversible sink of energy acting on the large scales,which can be exploited for large eddy simulations of turbulence (LES).Second, from a more theoretical perspective, we will see how the unidirectional coupling of the cascade is relevant to intermittency by playing a fundamental role in the emergence of intense coherent structures in the dissipative range. To conclude, we will discuss future research perspectives and open questions that materialize from these results.