EXTENDED UNIVERSALITY IN MODERATE-REYNOLDS-NUMBER FLOWS

In the inertial interval of turbulence one asserts that the velocity s tructure functions S(n)(r) scale like r(nzetan). Recent experiments in dicate that S. (r) has a more general universal form [rf(r/eta)]nzetan , where eta is the Kolmogorov viscous scale. This form seems to be obe yed on a range of scales that is larger than power law scaling. It is shown here that this extended universality stems from the structure of the Navier-Stokes equations and from the property of the locality of interactions. The approach discussed here allows us to estimate the ra nge of validity of the universal form. In addition, we examine the pos sibility that the observed deviations from the classical values of zet a(n) = 1/3 are due to the finite values of the Reynolds numbers and th e anisotropy of the excitation of turbulence.