  Recent developments in turbulence are focused on the effect of large scale
anisotropy on the small scale statistics of velocity increments. According to
Kolmogorov, isotropy is recovered in the large Reynolds number limit as the
scale is reduced and, in the so-called inertial range, universal features
-namely the scaling exponents of structure functions - emerge clearly. However
this picture is violated in a number of cases, typically in the high shear
region of wall bounded flows. The common opinion ascribes this effect to the
contamination of the inertial range by the larger anisotropic scales, i.e. the
residual anisotropy is assumed as a weak perturbation of an otherwise isotropic
dynamics. In this case, given the rotational invariance of the Navier-Stokes
equations, the isotropic component of the structure functions keeps the same
exponents of isotropic turbulence. This kind of reasoning fails when the
anisotropic effects are strong as in the production range of shear dominated
flows. This regime is analyzed here by means of both numerical and experimental
data for a homogeneous shear flow. A well defined scaling behavior is found to
exist, with exponents which differ substantially from those of classical
isotropic turbulence. Contrary to what predicted by the perturbation approach,
such a deep alteration concerns the isotropic sector itself. The general
validity of these results is discussed in the context of turbulence near solid
walls, where more appropriate closure models for the coarse grained
Navier-Stokes equations would be advisable.
