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THE HIGH SPEED
FRONTIER
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- Chapter 3: Transonic Wind
Tunnel Development (1940 -1950)
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- THE ANNULAR TRANSONIC
TUNNEL
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- [80] Not really a wind
tunnel at all in the usual sense, the Annular Transonic Tunnel
more properly falls in the "whirling-arm" category. It was also
variously referred to as the "Rotating-Disc Transonic
Research Equipment," "Special Transonic Research Equipment,"
"Annular-Throat Tunnel," and "Langley Transonic Tunnel." C. duP.
Donaldson proposed the scheme in late 1944, thinking of it as a
single-bladed axial fan rotating at transonic speeds. The single
blade or test airfoil had very small tip clearance with the
annular passage so that the flow
could
approach two-dimensionality. To
avoid wake interference a low-speed axial flow was induced in the
annular passage by a blower, and the boundary layers on both
surfaces of the annulus were removed ahead of the rotor
(fig.
18). In effect, the test airfoil
would be flying in a channel of infinite depth and choking would
not occur.
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- Of the several difficult problems of this
scheme, the most formidable...
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- [81] FIGURE 19.-Section through
axis of rotation of the pressure-transter device of B. W. Corson, Jr.
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- ....was the accurate determination of the
forces on the whirling test airfoil. In all probability the
annular tunnel would never have been attempted, and perhaps it
would never have been conceived at all, had it not been for the
invention, successful development, and prior use by our 16-foot
tunnel group of a pressure-transfer device which made it
possible to obtain accurate pressure distributions about the test
airfoil.
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- The design of the multiple-pressure
transfer device was proposed by Blake W. Corson, Jr., in 1943
(ref.
96) (see fig. 19). It was developed successfully by J. F. Runckel,
R. S. Davey, and M. F. Miller, in consultation with Corson,
substantially as proposed. It was used initially in a pressure
distribution study on the rotating blades of a 42-inch diameter
axial compressor (ref. 97). Davey later developed an improved transfer
[82]
device using mechanical seals which was used in the annular
transonic tunnel and in the high-speed propeller program
(ref.
98). The availability of the
original device was at the heart of the Annular Transonic Tunnel
enterprise.
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- Because of its close relationships to our
axial compressor research at the 16-foot tunnel, the Annular
Transonic Tunnel concept was placed in our group for design,
development, and exploitation. Much of our electrical equipment
could be used directly. A suitable cinder-block building was
erected on the 16-foot grounds to house the new tunnel. As one can
see in the photograph (fig. 20) the annular tunnel was a substantial new facility,
considerably exceeding the other small high-speed airfoil
tunnels in cost. Early in 1947 the first successful runs
were made (ref. 49), and the first pressure distributions ever
measured on an airfoil at Mach 1 were obtained (ref. 99).
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- After a 5-year life, the Annular Tunnel
was decommissioned in 1952.
It had major limitations: only
simple airfoils could be tested; the test process was cumbersome
(only 5 airfoils were tested in 5 years) ; for structural reasons
speeds above Mach 1were never attempted; and when the X-1 data and
semi-open-tunnel data became available, it was evident that the
Annular Tunnel pressures were uniformly too high by a small but
ever-present amount for which no explanation could ever be found
(ref.
100). There was obviously no
justification to continue the Annular Tunnel after the simple,
more productive semi-open, and the more versatile slotted tunnels
came into operation.
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- COMMENTARY
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- Public announcement of the Annular
Transonic Tunnel was made at the opening exercises of the May 1949
Biennial Inspection of the Langley Laboratory. To heighten the
emphasis, NACA called on John Stack to describe the
accomplishment. What was actually happening here, beyond the
revelation of an interesting new facility, was an unprecedented
attempt by NACA to divert attention away from the slotted
transonic tunnel developments. NACA subsequently admitted the dual
intent of this announcement in a rather surprising statement found
in the 40th Annual Report of 1954,
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- [83] FIGURE 20.-The
Annular Transonic Tunnel, opened at the rotor section. R. Turner,
left, and L. W. Habel.
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- it is to be doubted whether the NACA would
have given the [ATT] device the importance implied by the [1949]
public announcement except that it served to explain away rumors
that a successful transonic wind tunnel had been developed. Such
was in fact the case.... At the same time that the (1949]
announcement of the annular-throat wind tunnel was being made,
construction was being rushed towards completion of
the first of the large [slotted] transonic wind
tunnels.
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- By the time of Stack's public
announcement, it was already clear that the ATT had serious
deficiencies and very limited prospects; the semi-open 4 x 19-inch
facility had already proved itself and had taken up the entire
burden of the transonic airfoil program.
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- The necessity for NACA in 1954 to reveal
the dual nature of the 1949 ATT announcement is obvious. They were
saying in effect, "This time we are going to tell you about the
real transonic tunnel." It seems to have been taken for granted
that tactics of this kind were justified in the interest of
national security in the environment of the early fifties.
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- [84] I doubt that the
1949 announcement did much to divert attention from the slotted
tunnel; too many outsiders already knew about it.
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