Investigation of a Two-Step Nozzle in an 11-Inch Hypersonic Tunnel Page: 4 of 60
This report is part of the collection entitled: National Advisory Committee for Aeronautics Collection and was provided to UNT Digital Library by the UNT Libraries Government Documents Department.
Extracted Text
The following text was automatically extracted from the image on this page using optical character recognition software:
NACA RM L9G26
THE PROBLEM OF THE HYPERSONIC TUNNEL
As mentioned previously, this investigation was undertaken to study
the problems to be met in designing hypersonic tunnels. The most
important of these problems result from the following factors:
(1) The large area ratios
(2) The large pressure ratios across the system required to maintain
the flow
(3) The large decrease in free-stream temperature that takes place
through the nozzle
(4) The large variations in static pressure through the nozzle
The large area expansion from the first minimum, or M = 1 section,
to the test section, or final Mach number section (104.1:1 at M = 7),
creates many difficulties. In general, it means that the first minimum
area becomes very small and requires extremely accurate machine work.
The flow in the nozzle is also very sensitive to small boundary-layer
changes at the first minimum. For the approximately 10-inch-square
test section of the.nozzle used in this investigation, the first minimum
area is about I square inch. In a conventional two-dimensional nozzle,
this would amount to a slit 1/10 inch high and 10 inches wide, whereas
at a Mach number of 10 this slit would be reduced to a height of about
0.020 inch. Nozzles which avoid the need for a thin slit-like first
minimum are the two-step nozzle which may have an almost square throat
and the three-dimensional nozzle. The three-dimensional form of nozzle
involves many design problems, particularly if optical viewing of the
flow is required.
Also encountered at the high Mach numbers is the difficulty'of
providing the large pressure ratios required to drive the tunnel. ;For
example, the stagnation-pressure ratio across a normal shock at M 7
is about 65, while at M = 10 it becomes about 328. Use of these shock
losses as a rough index to the required pressure ratios indicates that,
with reasonable size and densities, large amounts of power will be
required to drive a hypersonic tunnel. Of course, by the use of second
minimums (that is, an area reduction after the test section) a
substantial reduction in the pressure ratio required to maintain flow
can be expected.
A third major obstacle to overcome in order to obtain a satisfactory
flow is the heating requirement. In order to maintain the static
temperature of the air above the liquefaction temperature in the test
section, the stagnation temperature must be increased to a point atCONFIDENTIAL
CONFIDENTIAL
Upcoming Pages
Here’s what’s next.
Search Inside
This report can be searched. Note: Results may vary based on the legibility of text within the document.
Tools / Downloads
Get a copy of this page or view the extracted text.
Citing and Sharing
Basic information for referencing this web page. We also provide extended guidance on usage rights, references, copying or embedding.
Reference the current page of this Report.
McLellan, Charles H.; Williams, Thomas W. & Bertram, Mitchel H. Investigation of a Two-Step Nozzle in an 11-Inch Hypersonic Tunnel, report, October 25, 1949; (https://digital.library.unt.edu/ark:/67531/metadc58362/m1/4/: accessed April 25, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.