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The experimental set-up of the rotating disk.
Mean azimuthal velocity profiles at R = 430 (○), 470 (*), 510 (×), 550 (□), 590 (◊), 630 (▽). Solid line is the laminar theory profile.
Profiles of v rms . The symbols are the same as in Fig 2.
Fourier power spectra for ensemble-averaged time series measured at z = 1.3 at (a) R = 430, (b) R = 470, (c) R = 510, (d) R = 550, (e) R = 590, and (f) R = 630.
v rms variance measured at z = 1.3 and a constant rotational speed Ω* = 1400 rpm. Solid and dashed lines are exponential fittings for each instability region given as v rms ∼ exp (αR), where α is the growth rate. These coefficients for solid and dashed lines are α = 0.058 and 0.017, respectively. Circles denote unfiltered signal, triangles show band-pass filtered signal (17 < ω*/Ω* < 70) below R ⩽ 490 and high-passed filtered signal (17 < ω*/Ω*) for 495 ⩽ R ⩽ 525.
The PDF of the filtered instantaneous azimuthal fluctuation velocity v at z = 1.3 normalized by the wall speed. Filled contours indicate 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, and 90% of the local PDF value.
The PDF of the instantaneous azimuthal fluctuation velocity normalized by the wall speed to show the z-structure at (a) R = 470, (b) R = 490, (c) R = 510, (d) R = 530, (e) R = 550, (f) R = 570, (g) R = 590, (h) R = 610, and (i) R = 630, namely cases P02 to P09 in Table I. Filled contours indicate same as Fig. 6. The range of the abscissa is −0.5 to +0.5 for all R. Note that in the free stream far above the disk, the positive values of v emanates from the high velocity fluid near the disk giving a positive skewness, i.e., the picture here is opposite to the one that would be observed for the flow over a stationary plate where the skewness is negative close to the boundary-layer edge. The white + signs in (e) and (f) show the position of the double peaks.
Experimental conditions, where r* and z represent the radial and axial positions of the probe, respectively.
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