An experimental study on axisymmetric turbulence. (2nd report. On the scales and the turbulence Reynolds numbers of the axisymmetric turbulence field).

Abstract

An axisymmetric turbulence field was generated behind honeycomb grids in a wind-tunnel test section. Integral and microscales were experimentally determined and their streamwise evolution was inspected. The aspect of the evolution differed from that of the quasi-isotropic turbulence, because it was influenced by the energy exchange between the spectral components of velocity fluctuations. The turbulence Reynolds numbers based on the integral scales became regardless of the degree of the anisotropy if the length scale was taken as the geometrical mean of the longitudinal and lateral integral scales. The turbulence Reynolds number based on the equivalent microscale was not free from the effect of the streamwise deformation of the spectra. These facts issue a warning to the easy application of the 'local-isotropy concept' on the anisotropic turbulence.