NACA Transonic Wing-Tunnel Test Sections Page: 3 of 95
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C I CA 18 NoM L JO6
fact, the very first efforts to construct high-speed wind tunnots were
made usn g openthroat tunnl. Lar ge power requirements and flow
u teadiness of open-throat tunels at high Mach numbers, however,
nter-posed s.eZrious disadvantages and thus closed,,throat .t..unnels were
employed. As the need for adequate .research facilities for the range of
Mach number near and throg 1.0 grew, new efforts were instituted to
solve the problem of wind-tuinel testing limitations for the ich
number 1.0 region. Fundamental considerations of the problem of win}d-
tunnel-wall corrections and choking limitations ledto to the idea of a
"porous wall.
Theoretical consideration of the problem with subsonic flow indicated
the possibility of reducing the interference due to boundaries by means
of slots in the solid boundary extending in the direction of flow. On
the basis of approximate theoretical results, such a slotted. wind tunnel
was designed. Tests of a model in this slotted wind tunnel indicated that
the primary object of minimizing the interference effects due to constric-
tion had- been attained., At the same time, the tests showed that the
slotted test section could be operated continuously through the transonic
range to low supersonic Mach numbers without change in tunnel configuration.
No theory has yet been developed for upper transonic and supersonic operation
The subsonic theo y was first developed in useful form in September 1946.
This paper presents the significant research results obtained to date.
S ONIC TORY
The first investigation un dertaken in this project was a theoretical
study of the solid blockage in a wind tunnel with cylindrical boundary
containing open slots parallel to the flow. It was thought possible,
since the interference velocities due to the walls are of opposite signs
with free and solid boundaries, that the opposite effects might be so
combined in a slotted tunnel as to produce zero solid blockage. The
theoretical development follows.
Consider a doublet placed on the axis of a circular slotted wind
tunnel (fig, i). On the assumption of incompressible potential flow, the
potential due to this doublet is
V (x2 F)
where
m the doublet strength
x coordinate in the axial direction
r radial cord inateCO14NF DENT ILl
('I '-) P, , I k T
J "U "UA"Ij
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Wright, Ray H. & Ward, Vernon G. NACA Transonic Wing-Tunnel Test Sections, report, October 25, 1948; (https://digital.library.unt.edu/ark:/67531/metadc57837/m1/3/: accessed April 25, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.