Heat transfer in oscillatory flow. Progress report, January 1983-December 1983 Page: 6 of 40
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c. Quality Control
Any periodicity externally added to a tunnel generates free-stream
turbulence. Existing unsteady flow facilities operate with turbulence
levels of the order of 1%. Careful studies require much lower turbu-
lence levels. To quiet the flow in our tunnel we studied the literature
on honeycombs and screens (Dryden and Abbott, 1948; Schubauer, Spangen-
berg and Klebanoff, 1948; Loehrke and Nagib, 1976; Wigeland, et al,
1978; Tan-atichat, et al, 1982) and contacted personally an expert in
the field (Nagib, 1983). As a result of our investigations, we
installed in the settling chamber a second set of finer honeycombs and 3
sets of fine screens.
Typical results are shown in Tables 1 and 2, obtained with an LDV
tracker and counter respectively. In this table, the tunnel speed and
the by-pass valve are controlled independently. It is surprising that
the by-pass system influences greatly the turbulence level, even though
it is far upstream of the test section. We have also performed an
exhaustive study of turbulence frequency spectra examples of which are
shown in Fig. 2.
d. Pressure Control '
The acceleration and deceleration of large masses of water induce
fluctuations of pressure that may exceed the strength of the plexiglass
structure. Moreover, the efficient operation of hydrogen bubbles
require pressure levels lower than the atmosphere. To control the pres-
sure level in the tunnel, we have installed a water trap and piping
which connects the system to a vacuum pump. A separate level indicator
was added and numerous valves as shown in Fig. 3.
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Telionis, D. P. & Diller, T. E. Heat transfer in oscillatory flow. Progress report, January 1983-December 1983, report, January 1, 1983; Blacksburg, Virginia. (https://digital.library.unt.edu/ark:/67531/metadc1069990/m1/6/: accessed July 16, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.