Ensembles, turbulence and fluctuation theorem.

The fluctuation theorem is considered intrinsically linked to reversibility and therefore its phenomenological consequence, the fluctuation relation, is sometimes considered not applicable. Nevertheless here is considered the paradigmatic example of irreversible evolution, the 2D Navier-Stokes incompressible flow, to show how universal properties of fluctuations in systems evolving irreversibily could be predicted in a general context. Together with a formulation of the theoretical framework several open questions are formulated and a few more simulations are provided to illustrate the results and to stimulate further checks.