Approach to isotropy in a smooth wall turbulent boundary layer

The approach to local isotropy in a smooth wall turbulent boundary layer is examined using measurements of velocity spectra and moments, up to order 4 , of velocity increments. The ratio of the measured spectrum of the wall no rmal velocity fluctuation v to that calculated using isotropy from the meas ured spectrum of the longitudinal velocity fluctuation u, depends mainly on the Kolmogorov-normalized local mean strain rate and the Taylor microscale Reynolds number. These parameters also affect in a systematic way the depa rture from isotropy of the u - v spectral correlation coefficient and of th e v increment moments. (C) 2000 The Japan Socity of Fluid Mechanics and Els evier Science B.V. All rights reserved.