CLOSURE-MODEL FOR INTERMITTENCY IN 3-DIMENSIONAL INCOMPRESSIBLE TURBULENCE

A simplified Lagrangian closure for the Navier-Stokes equation is used to study the production of intermittency in the inertial range of thr ee-dimensional turbulence. This is done using localized wave packets f ollowing the fluid rather than a standard Fourier basis. In this formu lation, the equation for the energy transfer acquires a noise term com ing from the fluctuations in the energy content of the different wave packets. Assuming smallness of the intermittency correction to scaling allows the adoption of a quasi-Gaussian approximation for the velocit y held, provided a cutoff on small scales is imposed and a finite regi on of space is considered. In these approximations, the amplitude of t he local energy transfer fluctuations can be calculated self-consisten tly in the model. Definite predictions on anomalous scaling are obtain ed in terms of the modified structure functions: [[E(l,a)](q)(R)], whe re [E(l,a,r,t)](R) is the part of the turbulent energy coming from Fou rier components in a band (a-1)k around k similar to l(-1), spatially averaged over a volume of size R similar to l/(a-1) around r. (C) 1995 American Institute of Physics.