Applications of auxiliary air injectors to supersonic wind tunnels Page: 2 of 55
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NACA RM A53101 3 1176 01434 7984
NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS
APPLICATIONS OF AUXILIARY AIR INJECTORS TO SUPERSONIC
By Joseph M. Spiegel; Robert U. Hofstetter, and
Donald M. Kuehn
& Adverse effects of high compression-ratio requirements for super-
sonic vind tunnels are discussed, together with the use of second throats
for alleviating these effects. The application of an air injector as an
auxiliary to a conventional wind tunnel is explained, and a one-
dimensional theory and experimental data are presented to demonstrate
the feasibility of the device for reducing starting and running compres-
sion ratios, but at the expense of an increase in power requirements.
For a continuous-operation wind tunnel of variable Mach number and con-
ventional compressor drive-unit, the installation of an air-injector
system can extend the Mach number range without surging the compressor
and can reduce starting difficulties. These results are obtainable
without any additional pumping equipment. For a blowdown-type wind
tunnel with a divergent diffuser, the installation of an air-injector
system can reduce starting loads, increase running time, and raise the
maximum operating Mach number. It should not be used when power is of
primary concern, except possibly as a device for controlling boundary
layer at mass ratios less than 0.2. A recommended design procedure is
provided for the application of the auxiliary-injector principle to
supersonic wind tunnels.
In the design of supersonic wind tunnels, a primary problem is the
large loss of total pressure which results from the deceleration of
supersonic flow in the. diffuser. This deceleration occurs in the form
of strong shock waves which, in turn, produce additional losses as a
result of their interaction with the boundary layer of the wind-tunnel
diffuser. Thus, the wind-tunnel drive system must provide sufficient
compression ratio (ratio of settling-chamber to diffuser-exit total
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Spiegel, Joseph M.; Hofstetter, Robert U. & Kuehn, Donald M. Applications of auxiliary air injectors to supersonic wind tunnels, report, November 25, 1953; (digital.library.unt.edu/ark:/67531/metadc60515/m1/2/: accessed January 20, 2019), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.