An experimental study on axisymmetric turbulence. (3rd Report, Anisotropy tensor, scale anisotropy and probability density distribution of axisymmetric turbulence).

Abstract

A homogeneous cigar-shaped axisymmetric turbulence field was experimentally analyzed. The anisotropy tensor, scale anisotropy and probability density distribution were obtained from velocity fluctuations. The behavior of these parameters was interpreted by a model of eddy structure and related to the streamwise evolution of the spectra. The isotropy was recovered at first by large-scale turbulent eddies and then by smaller ones. The axisymmetric turbulence did not attain complete isotropy but reached a quasi-equilibrium state with weak anisotropy in the far downstream region. The probability density distribution of turbulent fluctuation was distorted by the strong anisotropy and gradually approached a Gaussian distribution in the process of return to isotropy.