Reynolds number effects on the fine structure of uniformly sheared turbulence

This study is an experimental investigation of the fine structure of uniformly sheared turbulence within the framework of Kolmogorov's local isotropy theory. The fine structure was invoked from statistics of derivatives and differences of the streamwise velocity, in both the streamwise and transverse directions, for turbulence Reynolds numbers Re-lambda between 140 and 660. The streamwise derivative had a pdf with highly asymmetrical, stretched tails, which became more pronounced as Re-lambda increased. Its skewness grew slowly with Re-lambda, while its flatness increased at a higher rate, in conformity with previous studies. The transverse derivative had a pdf with a tail asymmetry that decreased as Re-lambda increased. Its skewness was positive and decreased from about 0.70 at Re-lambda=140 to about 0.34 at Re-lambda=660, while its flatness had values near 8.0 and increased only slightly with Re-lambda. The pdf and flatnesses of velocity differences suggested that intermittency in the inertial spectral range increased with a decreasing separation distance and increasing Re-lambda. Structure functions up to fourth order were compatible with Kolmogorov's hypotheses, while the sixth-order structure functions required some correction. (C) 2000 American Institute of Physics. [S1070-6631(00)50311-0].