The decay of anisotropic turbulence

We present the results of a numerical investigation of
three-dimensional decaying turbulence with statistically homogeneous
and anisotropic initial conditions. We show that at large times, in
the inertial range of scales: (i) isotropic velocity fluctuations
decay self-similarly at an algebraic rate which can be obtained
by dimensional arguments; (ii) the ratio of anisotropic to isotropic
fluctuations of a given intensity falls off in time as a power law,
with an exponent approximately independent of the strength of the
fluctuation; (iii) the decay of anisotropic fluctuations is not
self-similar, their statistics becoming more and more intermittent as
time elapses. We also investigate the early stages of the decay.
The different short-time behavior observed in two experiments differing
by the phase organization of their initial conditions gives a new hunch on
the degree of universality of small-scale turbulence statistics, i.e. its
independence of the conditions at large scales.