ANISOTROPY OF THE SPECTRUM OF TURBULENCE AT SMALL WAVE-NUMBERS

Abstract

In a previous paper it has been shown theoretically that the tendency to isotropic turbulence does not exist for the large-scale components of homogeneous turbulence. This paper provides experimental evidence that the large-scale components of turbulence behind a grid in a uniform stream are anisotropic, even though the total turbulent energy may be distributed with approximate spherical symmetry. The evidence consists (a) of a comparison between two different velocity correlations for large spatial intervals, in the initial period of decay, and (b) of measurements of the directional distribution of turbulent energy in the final period of decay when all except the large-scale components of the motion have been greatly reduced by viscous decay.