Extended self-similarity in anisotropic grid-generated turbulent flow

The form of scaling called Extended Self-Similarity (ESS) is investigated experimentally in a grid-generated turbulent how at low Reynolds number. Measurements are conducted by means of single probe Hot Wire Anemometry (HWA). The how is first analyzed in order to localize qualitatively the anisotropic region downstream of the grid, and then the statistical properties of the small scale fluctuations are investigated by means of ESS scaling. The efficacy of ESS is verified by measuring velocity fluctuations in two positions downstream of the grid (x/M = 9 and 163) and by determination of the low-order (1 to 6) statistical moments of the velocity spatial difference. For each measurement position a scaling is observed which allows the intermittency exponents to be detected accurately. It is then found that ESS is valid even for non-isotropic and non-homogeneous large scale conditions (i.e. a few mesh lengths downstream of the grid). The effect of the anisotropy on the magnitude of the scaling exponents is also analyzed by comparison with previous investigations in homogeneous turbulence. A low sensitivity of the scaling range extensions with respect to decreasing distance from the grid (i.e. for flow conditions varying from isotropic to anisotropic turbulence) is also detected.