A device is described which changes the Mach number capability of a wind tunnel without permanently altering the existing nozzle of the tunnel. An insert is removably attached to the wall of the existing nozzle expansion area thereby creating a second minimum section upstream of the model test section. The added insert may be removed without complicated and expensive changes to the basic wind tunnel. In one embodiment, a removable insert is disposed within wind tunnel nozzle walls with a portion of the flow boundary layer being bled off from the tunnel via passageway and tunnel exit to reduce the extent of separated flow normally occuring upstream of the insert contraction section

Couch, L. M.

English

NASA Technical Reports Server

United States Patent [191 11 11 4,286,460 
Couch WI Sep. 1, 1981 
[54] WIND TUNNEL SUPPLEMENTARY MACH 
[75] Inventor: Lana M. Couch, Mathews, Va. 
[73] Assignee: The United States of America as 
NUMBER MINIMUM SECTION INSERT 
represented by the Administrator of 
the National Aeronautics and Space 
Administration, Washington, D.C. 
[21] Appl. No.: 135,040 
[22] Filed: Mar. 28, 1980 
[51] Int. Cl.3 .............................................. GOlM 9/00 
[52] U.S. C1. ...................................................... 73/147 
[58] Field of Search .......................................... 73/147 
[561 References Cited 
U.S. PATENT DOCUMENTS 
3,011,341 12/1961 Hill ......................................... 73/147 
FOREIGN PATENT DOCUMENTS 
712706 10/1941 Fed. Rep. of Germany ............. 73/147 
Primary Examiner-Donald 0. Woodiel 
Attorney, Agent, or Firm-Howard J. Osborn; John R. 
Manning; Wallace J. Nelson 
[571 ABSTRACT 
The invention relates to a device which changes the 
Mach number capability of a wind tunnel without per- 
manently altering the existing nozzle of the tunnel. An 
insert (14) is removably attached to the wall (17) of the 
existing nozzle expansion area (22) thereby creating a 
second minimum section (15) upstream of the model test 
section (21). The added insert (14) may be removed 
without complicated and expensive changes to the basic 
wind tunnel. In the embodiment illustrated in FIG. 2, a 
removable insert (25) is disposed within wind tunnel 
nozzle walls (17) with a portion of the flow boundary 
layer being bled off from the tunnel via passageway (29) 
and tunnel exit (28) to thereby reduce the extent of 
separated flow normally occuring upstream of the insert 
contraction section. 
5 Claims, 2 Drawing Figures 
21 
https://ntrs.nasa.gov/search.jsp?R=19820003215 2020-03-21T15:28:42+00:00Z
U.S. Patent Sep. 1,1981 Sheet 1 of 2 4,286,460 
U.S. Patent Sep. 1,1981 Sheet 2 of 2 4,286,460 
1 
4,286460 
WIND TUNNEL SUPPLEMENTARY MACH 
NUMBER MINIMUM SECTION INSERT 
ORIGIN OF THE INVENTION 
The invention described herein was made by an em- 
ployee of the United States Government and may be 
manufactured and used by or for the Government for 
governmental purposes without the payment of any 
royalties thereon or therefor. 
BACKGROUND 
Wind tunnels are tubelike structures or passages in 
which a high-speed wind or gas stream is produced and 
within which objects such as engines, aircraft, airfoils, 
rocket missiles or scale models of these objects are 
placed to investigate the air flow about them and the 
aerodynamic forces acting upon them. Wind tunnels are 
designed to simulate forces acting on the test object to 
which the full size object would be subjected if it were 
in actual flight. 
Most wind tunnel nozzles create a high speed gas 
stream by supplying a compressed gas, usually air, to a 
converging-diverging nozzle which accelerates and 
expands the pressurized gas and forms it into a high 
speed gas stream. The converging-diverging nozzle 
usually comprises an inlet section whose cross-sectional 
area decreases in the direction of flow through the noz- 
zle, and a diverging outlet section, usually of relatively 
great length, whose cross-sectional area increases in the 
direction of flow through the nozzle, with a “throat” 
joining the converging and diverging sections. 
As is well known in the high speed gas dynamic art, 
the speed ultimately attained by the gas accelerated in a - -  
wellldesigned converging-diverging nozzle depends 
upon the “area ratio” of the nozzle, that is, the ratio of section, and thereby, decreases the maximum model size 
the CrOSS-SeCtiOnal area O f  the nozzle passageway at its that can be tested. Third, any change of Mach numbers 
exit to the cross-sectional area at its throat. Thus, by would require considerable time, thereby decreasing 
preselecting the area ratio of the nozzle, the ultimate the efficiency of the testing procedure. Fourth, the 
’peed Of the gas can be made “transonic” 40 replaceable nozzle system can adversely affect the abil- 
air), or “supersonic” (substantially greater than Mach 
’), or ~‘hypersonic,, (very much greater than Mach ’). combustion wind tunnel. Fifth, with a system using an 
The construction of wind tunnels is expensive and adjustable first minimum section, not only would the 
involves elaborate and sophisticated technology. With 45 installation cost probably be prohibitive, but also the 
the supersonic and hypersonic tunnels, the area ratio of increased mechanical complexity of any device de- 
the nozzle must be made extremely large in order to signed to vary the area ratio of the nozzle would neces- 
produce the desired wind speeds. A large area ratio sarily increase the probability of malfunction and distor- 
usually is attained by making the throat area small as tion of the high speed gas stream. Finally, maintenance 
possible rather than by making the exit area larger. This 50 of such a system would be costly and time consuming. 
is done in order to make the wind tunnel test section of Thus, a need continues to exist for an inexpensive 
reasonable size and as inexpensive as possible, and in wind tunnel system providing variable Mach numbers 
order to minimize the quantity of gas flow through the in a fixed nozzle wind tunnel. 
nozzle and thus minimize the required capacity of the Accordingly, it is an object of the present invention 
system used to supply compressed gas to the wind tun- 55  to provide a means for quickly and inexpensively 
changing the Mach number capability of a wind tunnel. nel. To maximize the area ratio of the nozzle, the cross- Another object of the present invention is to provide 
sectional area at the throat can be minimized. The a device which can vary the Mach number capability of throat area is minimized by making the passage connect- a wind tunnel without altering the original wind tunnel ing the converging and diverging sections as small as 60 
possible. Often, the throat height or spacing will be only structure. 
greater Or less than Mach ‘ 9  Or the ’peed Of sound in ity to sustain or even start a combustion process in a 
a few hundredths of an inch. With such minute spat- by the 
ings, the slightest deformation of the throat structure is Present invention by using an insert Positioned in the 
likely to cause substantial distortion of the gas stream. nozzle expansion area to create a second minimum set- 
Consequently, most wind tunnels are designed with 65 tion. The insert comprises a converging inlet area and a 
nozzles which are relatively immutable. diverging exit area and can be quickly attached or re- 
If the cross-sectional area of the throat section cannot moved. Unlike the prior art methods, the basic structure 
be changed, then the ultimate Mach number capability of the wind tunnel nozzle is never altered. 
These and Other Objects are 
2 
of the wind tunnel cannot be varied. However, re- 
searchers often wish to test aerodynamic models at 
variable Mach numbers. Thus, designers have sought 
ways to change the cross-sectional area of the throat 
section to provide supplementary Mach numbers with- 
out sacrificing the precision of the wind tunnel perfor- 
mance characteristics. 
PRIOR ART 
Previous methods for providing additional Mach 
numbers in a fixed nozzle wind tunnel have included 
either (1) changing the area of the original first mini- 
mum section plus recontouring the original nozzle to 
15 provide the area ratio required for the desired test sec- 
tion Mach number, or (2) recontouring the original 
nozzle plus changing the original nozzle exit area to 
provide the area ratio required for the desired test sec- 
tion Mach number. 
With either method, the first minimum section has to 
be designed either to be replaceable with a first mini- 
mum section of different dimensions, or the design must 
provide a means of adjusting the area ratio and contour- 
25 ing of the nozzle. These prior art methods entail numer- 
ous disadvantages. First, replacement of the original 
first minimum section and contoured nozzle usually is 
an excessively expensive operation. Second, increasing 
the original throat diameter to lower the Mach number 
30 would result in a much longer nozzle than a typical 
lower-Mach-number nozzie. Therefore, boundary layer 
would have a longer distance to gfow and would be 
much thicker than usual for that Mach number and 
would occupy a large portion of the test section area. 
35 This decreases the diameter of uniform flow in the test 
10 
2o 
4,286,460 
3 4 
second minimum section 15 to a value greater than one 
but less than the Mach number desired at model test 
A more complete appreciation of the invention and section 21. The desired Mach number would then be 
many of the attendant advantages thereof will be attained by conventional expansion of the gas stream 
readily attained as the same becomes better understood 5 through contoured expansion section 19. 
by reference to the following detailed description when Alternatively, insert 14 can restrict the flow of the 
considered in COnnectiOn with the accompanying draw- gas stream sufficiently to produce Mach one at second 
ings, wherein: minimum section 15. Conventional expansion of the gas 
FIG. 1 is a section view of the preferred embodiment stream provided by contoured expansion section 19 
Of a wind tunnel nozzle insert according to the present 10 would then accelerate the gas stream to the desired 
invention; and Mach number at model test section 21. 
FIG. 2 is a section view of a nozzle insert according In a specific example of the first alternative, an eight- 
to the present invention and mounted in spaced relation- foot hypersonic wind tunnel with a fixed nozzle 11 
ship with the wind tunnel wall. having an area ratio of essentially 104:l (area of nozzle 
DETAILED DESCRIPTION OF T H E  l5 exit to nozzle throat area) typically would provide a 
INVENTION nominal Mach number of seven at model test section 21 
before the addition of insert 14. Once insert 14 is at- 
ne1 10 having a throat 12 and a nozzle 11. An insert 14 number just upstream of insert 14 where the flow is 
exit area walls 17, with conventional seals provided about four. After passage through second minimum 
between the and to prevent leakage' section 15, the gas stream accelerates through insert 
Insert 14 comprises a contoured contraction section 18 expansion area 22 to model test section 21 where the 
made of various materials depending on the gas energy 25 . insert 14 reduces the nominal Mach number at model level, that is, the combined temperature-pressure effect, test section 21 from seven to five without altering fixed of the wind tunnel. For example, with a low energy nozzle 11. Different inserts would be employed for each tunnel, aluminum, fiberglass-covered wood or wood 
would be suitable while in a high energy tunnel, steel, desired Mach number in a specific 
would be preferable. Finally, for a very high energy shown an embodiment of the invention in which con- 
could be used. With a high energy tunnel, the bolt at- ders or spacers 26 for securing insert 25 to nozzle expan- 
tachment points would be designed to accommodate 35 sion area walls 17 but while also serving to maintain a 
the expansion of the insert material. Insert 14 may be of terminated Passageway 29 between insert 25 and nozzle 
unitary or sectional construction. However, in the pre- expansion area 17. As air flow Passes through 
ferred embodiment, insert 14 would be manufactured in 11, boundary layer thickness develops. This 
two or more sections to facilitate attachment to the boundary layer flows through passageway 29 from 
wind tunnel wall. 40 which it is removed from wind tunnel 10 through exit 
In the operation of a typical wind tunnel, a high speed Passageway 28 as shown by flow arrow 27. Bleeding Off 
gas stream enters nozzle 11 passing downstream the boundary layer can reduce the extent of separated 
through first minimum section 15 toward nozzle exit flow that would occur immediately upstream of insert 
area 16 as shown by the flow arrow indicated by nu- Contraction Section 30. Insert 25 is contoured On all 
meral20. Conventionally, the Mach number of the gas 45 sides to acC0mmdate both the flow through ~ c o n d  
stream at throat 12 is equal to one. Nozzle 11 has an minimum section 15 and the flow through passageway 
expansion section which accelerates the gas stream to a 29. 
higher Mach number at the model test section. By at- The illustrations described herein are intended 
taching the second minimum section insert 14 to the merely as illustrations of possible embodiments of the 
nozzle expansion area walls 17, the conventional expan- 50 invention. The invention is not limited thereby and 
sion of the gas stream downstream of first minimum many modifications and variations thereof will be 
section 13 is terminated and the velocity of the gas readily apparent to those skilled in the art without de- 
stream is reduced. Contoured contraction section 18 of parting from the spirit and scope of the instant inven- 
insert 14 functions to decelerate and direct the gas tion. 
stream through second minimum section designated by 55 What is claimed as new and desired to be secured by 
reference numeral 15. Once the gas stream emerges Letters Patent of the United States is: 
from second minimum section 15, it passes through 1. In combination with a wind tunnel having a nozzle 
contoured expansion section 19 which is designed to with a first minimum section and a nozzle expansion 
cancel spurious shock waves and conventionally accel- area having walls, an apparatus for providing supple- 
erate the gas stream to the Mach number desired at 60 mentary wind tunnel Mach numbers, said apparatus 
model test section 21. The dimension, shape and loca- comprising a second minimum section insert releasably 
tion of insert 14, as well as the minimum diameter of the attached to said walls of said nozzle expansion area of 
passage of second minimum section 15, depend on the said wind tunnel. 
Mach number desired in model test section 21, and the 2. An apparatus as in claim 1, whereby said second 
existing nozzle exit area Mach number and Mach num- 65 minimum section insert releasably attached to said walls 
ber development rate with distance along nozzle 11. of said nozzle expansion area comprises a contoured 
Insert 14 can restrict the flow of the gas stream suffi- contraction section, a contoured expansion section, and 
ciently to reduce the Mach number of the gas stream at a minimum area passage connecting said contoured 
DESCRIPT1oN OF THE 
Referring now to '9 there is shown a wind tun- tached to nozzle expansion area walls 17, the Mach 
Zo decelerated by second minimum section 15, would be is removably attached by bolts (not shown) to 
and a expansion section 19' Insert l4 can be Mach number would be about five. Thus, installation of 
nickel, or a metal covered with a ceramic coating 30 
tunnel, a high temperature resistent metal, an actively 
cooled metal, or a metal covered with a ceramic coating 
Referring now more particularly to 2, there is 
toured i's& 25 is attached by bolts (not shown) extend- 
ing through or other temperature resistent cylin- 
4,286,460 
5 6 
contraction section with said contoured expansion sec- 
tion. 
3. An apparatus as in claim 1, whereby said second 
minimum section insert is contiguous with said walls of 
said nozzle expansion area. 5 
4. An apparatus as in claim 1, whereby said second 
minimum section insert is spaced from said walls of said 
nozzle expansion area thereby providing a terminated 
passageway between said second minimum section in- 
sert and said walls of said nozzle expansion area, and 10 
means for bleeding off wind tunnel flow between said 
insert and said walls. 
5. A method for varying the Mach number capability 
of a wind tunnel which comprises: 
providing a wind tunnel having a nozzle with a first 15 
minimum section and a nozzle expansion area hav- 
ing walls; 
providing a releasably attachable second minimum 
section having a contoured canverging and con- 
20 
traction section, a contoured diverging and expan- 
sion section, and a minimum area passage connect- 
ing the contraction section with the expansion sec- 
tion; 
adjusting the diameter of the passage connecting the 
contraction section with the expansion section of 
the second minimum section insert relative to the 
nozzle exit area to provide a desired Mach number 
capability; 
positioning the insert on the walls of the nozzle ex- 
pansion area relative to the nozzle to provide a 
desired Mach number capacity; and 
providing a flow of gas through the first minimum 
section of the nozzle and through the second mini- 
mum section insert, whereby the Mach number of 
the gas stream at the nozzle exit area is determined 
by its passage through the second minimum section 
insert. * * * * *  
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Wind tunnel supplementary Mach number minimum section insert

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