To test the local-isotropy predictions of Kolmogorov's (1 941) universal equilibrium theory, we have taken hot-wire measurements of the velocity fluctuations in the testsection-ceiling boundary layer of the 80 x 120 foot Full-Scale Aerodynamics Facility at NASA Ames Research Center, the world's largest wind tunnel. The maximum Reynolds numbers based on momentum thickness

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In this paper the fractal nature of velocity signals as measured in turbulent Bows is investigated. In particular, we study the geometrical nature of the graph (x,f(x) ) of the function f that gives one component of the velocity at position x. Special emphasis is given to the effects that a limited resolution of the signal, or natural small-scale cutoffs, have on the estimate of the fractal dimension, and a procedure to account for such finite-size effects is proposed and tested on artificial fractal graphs. We then consider experimental data from three turbulent Aows: the make behind a circular cylinder, the atmospheric surface layer, and the rough-wall zero-pressure-gradient boundary layer developing on the test-section ceiling of the 80X 120 ft full-scale NASA Ames wind tunnel (the world's largest wind tunnel). The results clearly indicate that at high Reynolds numbers, turbulent velocity signals have a fractal dimension of D =1.7+0.05, very near the value of D= -', expected for Gaussian processes with a --', power law in their power spectrum.

Extensive experimental studies are presented of the effects of prolonged streamline divergence on developing turbulent boundary layers. The experiment was arranged as source flow over a flat plate with a maximum divergence parameter of about 0.075. Mild, but alternating in sign, upstream-pressure-gradient effects on diverging boundary layers are also discussed.It appears that two overlapping stages of development are involved. The initial stage covers a distance of about 20 initial boundary-layer thicknesses (δ0) from the start of divergence, where the coupled effects of pressure gradient and divergence are present. In this region there is a fairly large reduction in divergence parameter, Rθ (Reynolds number based on momentum thickness) remains constant (≈ 1400) and the boundary-layer properties change rapidly. In the second region, which lasts nearly to the end of the diverging section, the pressure-gradient effects are negligible, the rate of decrease in divergence parameter is very small and Rθ increases gradually. Up to the last measurement station (≈ 100δ0) the flow is still considered to be at a low Reynolds number (Rθ ≈ 2000). For almost the entire length of this region, the profiles of non-dimensional eddy viscosity appear to be self-similar, but have larger values than for the unperturbed flow. Also in this region, beyond 35δ0, the wake parameter, which has reduced significantly, becomes nearly constant and independent of Rθ. On the other hand the entrainment rate attains a constant value at around 50δ0. It appears that the boundary layer reaches a state of equilibrium. It is suggested that this is the result of an enhanced turbulent diffusion to the outer layer. Spectral measurements show that divergence affects mainly the low-wavenumber, large-scale motions. However, there is no change in large-eddy configurations, since the dimensionless structure parameters show only negligible deviations from the unperturbed values.