Anomalous scaling exponents and coherent structures in high Re fluid turbulence

The scaling exponents of the velocity structure functions are predicted by a simple model based on the probability density function (PDF) of the local turbulent kinetic energy fluctuations with no hypotheses on the shape of t he most intermittent coherent structures. The energy fluctuations are presu med to be induced by statistically independent coherent structures and, the refore, are characterized by exponential-like PDFs. Accounting also for the scaling of the energy with the scale, a recursive formula is obtained whic h permits the calculation of the scaling exponents of the velocity structur e functions. The predicted exponents are checked to be in good agreement wi th previous theoretical and experimental results. The main hypotheses behin d the present approach are also validated by analyzing experimental velocit y time series acquired in a jet flow at moderately high Re-lambda. It is al so shown that present approach allows the calculation of the scaling expone nts also in cases of nonhomogeneous turbulence. (C) 2000 American Institute of Physics. [S1070-6631(00)02302-3].