The asymmetric adjustable supersonic nozzle for wind-tunnel application Page: 2 of 31
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TECH LIBRARY KAPB, NM
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NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS 0 06006
TECHNICAL NOTE. 2919
TEE ASYMMETRIC ADJUSTABLE SUPERSONIC NOZZLE
FOR WIND-TUNNEL APPLICATION
By K. Julian Allen
The development of an asymmetric type of adjustable supersonic
nozzle suitable for application to wind tunnels is described. This new
type of nozzle permits continuous adjustment of the test-section Mach
number without the requirement of flexible walls. Uniformity of flow
within the test section as well as the compression ratio required for
the attainment of the supersonic flow are considered.
The advantages and disadvantages of this nozzle relative to the
conventional interchangeable-fixed-block and flexible-wall nozzles
In the design of any wind tunnel, the attainment of a uniform
velocity stream in the test section is the prime consideration. The
velocity gradients parallel and normal to the test-section center line
must be small in order that the results of aircraft model tests may be
applied with confidence to the determination of the free-flight aircraft
behavior. To determine the effects of compressibility on the aerodynamic
characteristics of aircraft models in the conventional type of wind tun-
nel, the test-section airspeed must, in addition, be adjustable.
In the familiar subsonic wind tunnel, neither of these requirements
is difficult to obtain. An entrance nozzle, the walls of which provide
a smooth and continuous passage from the air entrance through the flat-
walled test section, will suffice to prevent important gradients normal
to.the tunnel axis. In a nonviscous fluid, zero axial velocity gradients
at the test section would obtain with parallel and flat walls at the test
section, but for a real fluid same flare of the walls must be provided to
a allow for the growth of the boundary layer along the nozzle surfaces.
With such a tunnel, the test-section airspeed may be very conveniently
adjusted by changing the rotational speed of the driving fan or compressor.
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Allen, H. Julian. The asymmetric adjustable supersonic nozzle for wind-tunnel application, report, March 1953; (https://digital.library.unt.edu/ark:/67531/metadc56650/m1/2/: accessed April 24, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.