Isotropy vs anisotropy in small-scale turbulence

The decay of large-scale anisotropies in small-scale turbulent flow is inve stigated. By introducing two different kinds of estimators we discuss the r elation between the presence of a hierarchy for the isotropic and the aniso tropic scaling exponents and the persistence of anisotropies. By direct mea surements on a channel flow numerical simulation we show that the presence of a hierarchy for the isotropic and the anisotropic scaling exponent is no t in contradiction with the persistence of anisotropies at small scales. (C ) 2001 American Institute of Physics.