Local power fluctuations in two-dimensional turbulence

The statistics of power fluctuations are studied in simulations of two-dimensional turbulence in both inverse (energy) and direct (enstrophy) cascade regimes from both Lagrangian and Eulerian perspectives. The probability density function (PDF) of the appropriately defined dimensionless power is strongly non-gaussian with asymmetric exponential tails. This distribution can be modeled by the distribution of the product of correlated normal variables allowing a derivation of the asymptotics of the tails. The PDF of the dimensionless power is shown to exhibit an empirical Fluctuation Relation. An expression for the entropy production rate is deduced from the asymptotic form of the power PDF and is found to agree very well with the measured entropy rate.
Comment: 5 Pages and 3 figures. Revised version contains additional results for Eulerian power fluctuations, better presentation of the data to facilitate easy comparison between different regimes and an explanation for the value of the entropy rate in the empirical Fluctuation Relation