Component and over-all performance evaluation of an axial-flow turbojet engine over a range of engine-inlet Reynolds numbers Page: 7 of 44
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NAOA RM E52B08
from about 7750 rpm at a flight Mach number of 0.2 to about 5450 rpm
at a flight Mach number of 1.3. The data of this report may be used
to determine performance only at flight conditions in the choked
region above this curve.
In order to aid in determining the Reynolds number index corres-
ponding to a given flight condition and thereby determine the engine
performance at NACA standard altitude conditions from the generalized
data presented, the values of 8, e, $, and Reynolds number index are
given in table II for a wide range of flight conditions; 100 percent
ram-pressure recovery was assumed.
Compressor performance characteristics are presented in figure 6
for the range of Reynolds number indices investigated. The decrease in
compressor efficiency encountered with the reduction in Reynolds number
index is shown in figure 6(a). The peak compressor efficiency occurred
at a corrected engine speed of about 7000 rpm for all Reynolds number
indices investigated and decreased from 82. percent to 78 percent as
Reynolds number index was decreased from 0.95 to 0.2 (corresponding to
an increase in altitude from 10,000 to 50,000 ft at a flight Mach num-
ber of 0.7). Corrected compressor air flow is shown as a function of
corrected engine speed over the range of Reynolds number indices investi-
gated in figure 6(b), At Reynolds number indices of 0.4 and above,
corrected air flow generalized at corrected engine speeds below about
7200 rpm. At a corrected engine speed of 8000 rpm, the corrected com-
pressor air-flow decreased from 90.7 to 86.0 pounds per second as
Reynolds number index was decreased from 0.95 to 0.2. The ratio of
midframe air-bleed to compressor air flow is presented in figure 7 as
a function of the ratio of compressor outlet total pressure to ambient
static pressure. The engine air flow is equal to the compressor air
flow minus the midframe air-bleed. The decrease in efficiency and-air
flow will shift the compressor operating point (equilibrium point with
the turbine) because of the increase in work required of the turbine.
The amount of this shift is illustrated in figure 6(c). Although the
compressor operating lines shifted as Reynolds number index was reduced,
the simultaneous decrease in air flow and increase in turbine-inlet
temperature due to the loss in efficiency was such that the variation
of compressor pressure ratio with corrected engine speed generalized
for all Reynolds number indices investigated as shown in figure 6(d).
Variation of the total-pressure-loss ratio across the combustor
with corrected engine speed is shown in figure 8(a). Over the range of
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Walker, Curtis L.; Huntley, S. C. & Braithwaite, W. M. Component and over-all performance evaluation of an axial-flow turbojet engine over a range of engine-inlet Reynolds numbers, report, July 10, 1952; (https://digital.library.unt.edu/ark:/67531/metadc59177/m1/7/: accessed April 21, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.