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Mechanical, Materials and Aerospace Engineering
Illinois Institute of Technology
Abstract-
The two experiments of Österlund and Hites (e.g., see note in Phys. Fluids, vol. 12,
no. 1, p. 1, 2000) have been recently extended to Reynolds numbers based on momentum
thickness exceeding 70,000. The present measurements are carried out on a flat plate
in zero-pressure gradient in the National Diagnostic Facility (NDF). As in our
previous work, the wall shear stress is directly measured using oil-film
interferometry and hot-wire anemometry is utilized to measure the velocity. Contrary
to the recent conclusions of Barenblatt, Chorin and Prostokishin (JFM, vol. 410, p.
263, 2000, and Phys. Fluids, vol. 12, no. 9, p. 2159, 2000; see also our comment on
page 2360 of the same issue), the mean velocity distribution in the overlap region for
these higher Reynolds number boundary layers continues to be very accurately described
by the Reynolds-number-independent log law. Our work has established that the subtle
differences between the two relations representing the overlap region, and the data,
can only be revealed with the aid of the derivatives of the velocity with respect to
the distance from the wall; particularly when only low to moderate Reynolds number
experiments are available. As concluded from the earlier two experiments, the values
of the log-law coefficients that best represent the data are k = 0.38 and B = 4.1.
In addition, the data from four independent investigations of turbulent flow through
two-dimensional channels and pipes have been examined using the same techniques to
establish which of the two relations is more representative. These investigations
include DNS, LDV and PIV of the channel flow, and the Pitot-probe measurements in the
"super-pipe" experiment. Recent re-interpretations of the superpipe results by Tony
Perry and his colleagues will be mentioned. Finally, brief comments will also be
included on asymptotic analyses of turbulent boundary layer and channel flows with an
emphasis on the wall region and the various ways of scaling the outer flow.
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