ONSET OF INTERMITTENCY IN 2-DIMENSIONAL DECAYING TURBULENCE

The statistics of two-dimensional flow decaying from an initially Gaus sian velocity field are investigated both theoretically and numericall y. During the initial stages of the turbulence decay, small-scale inte rmittency develops. while the intermediate and large scales remain ess entially Gaussian. Corresponding to these early times, an expression d escribing the evolution of the shape of the probability density P(Omeg a,S-4) is derived from the Navier-Stokes equations, where Omega = omeg a/omega(rms) is the normalized vorticity and S-4 is the normalized fou rth-order moment of the vorticity. Predictions of the theory, which do es not involve adjustable parameters, agree with the results of numeri cal simulations for the early-time decay.