Applications of auxiliary air injectors to supersonic wind tunnels Page: 4 of 55
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NACA RM A53I01
the auxiliary air injector presents some attractive features on the
basis of the incompatibility between conventional air-compressor charac-
teristics and supersonic-wind-tunnel requirements. If the air that
must be bypassed to prevent compressor surge is channeled to an auxil-
iary injector, an improvement in both starting and running characteris-
tics of the wind tunnel would be expected.
In this report a one-dimensional analysis of the auxiliary-injector
principle is presented, together with some experimental results. Exam-
ples are given that demonstrate the improvement in operating character-
istics of both intermittent- and continuous-operation wind tunnels from
the standpoint of compression-ratio reduction.
& a sonic velocity, ft/sec
A cross-sectional area, sq ft
C any constant
cp specific heat at constant pressure, ft2/sec2Or
K stagnation pressure ratio, P-
injector mass flow
m mass-flow ratio, injector mass flow
test-section mass flow
M Mach number
P power, ft-lb/sec
p static pressure, b/sq ft abs
Q flow quantity, based on compressor intake conditions, cu ft/min
r compression ratio
rf correction factor,
R perfect-gas constant, ft2/sece/oF
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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/m1/4/: accessed December 13, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.