Transverse and longitudinal scaling laws in non-homogeneous low Re turbulence

The statistical properties of the velocity fluctuation components at moderate Rr, are studied in homogeneous and non-homogeneous turbulence by an experimental technique. Measurements are performed by means of a hot-wire anemometer with X-probe downstream of a screen for several positions, x/M=9 up to 109, where M is the screen mesh size, with Re-lambda ranging from 37 to 82. The homogeneity of the flow is analyzed by means of velocity measurements in different transverse positions and a direct evaluation of the local isotropy of the flow is performed by means of velocity spectra. The scaling properties of the statistical moments of the structure functions up to the order of six, are investigated in the extreme positions by means of the extended self-similarity (ESS) method and the intermittency exponents are detected for both homogeneous and non-homogeneous flow conditions. A comparison of the longitudinal and transverse intermittency exponents as functions of the position is then performed and discussed in addition to the analysis of the transition from the anomalous to a regular scaling for small spatial separation. (C) 1996 American Institute of Physics.