Equilibrium Operating Performance of Axial-Flow Turbojet Engines by Means of Idealized Analysis Page: 1 of 12
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EQUILIBRIUM OPERATING PERFORMANCE OF AXIAL-FLOW TURBOJET ENGINES
BY MEANS OF IDEALIZED ANALYSIS
By JOHN C. SANDERS and EDWARD C. CHAPIX
A method of predicting equilibrium operating performance of
turbojet engines has been developed, with the assumption of
.simple model processes for the components. Results of the
analysis are plotted in terms of dimensionless parameters
comprising critical engine dimensions and over-all operating
This investigation was made for an engine in which the ratio
of axial inlet-air velocity to compressor-tip velocity is con-
s.tant, which approximates turbojet engines z.with axial-flow
Experimental correlation of the theory with data from several
existing axial-flow-type engines was good and showed close
correlation between calculated and measured performance.
The equilibrium operating performance of a turbojet engine
can be predicted from a knowledge of the component char-
acteristics and -the engine-design variables. A method of
obtaining equilibrium performance is presented in reference 1.
This method consists in considering the engine by its com-
ponents (compressor, burner, turbine, and exhaust nozzle)
and computing over-all performance from the given charac-
teristics of each component. Because component charac-
teristics are so complex and there are so many variables,
computations based on available analyses are lengthy and
are also limited to a single engine and operating point for
any one series of calculations. A definite need exists for a
more general form of analysis that will permit an approximate
prediction of the performance of any engine configuration
at any flight speed or altitude based on several critical
dimensions and operating variables.
The first step in such an analysis is that of describing
complicated component processes in some simplified manner.
A method often successfully used is that of approximating
actual processes by means of simple model processes with the
final accuracy dependent on the degree of model refinement.
Some work has already been done in approximating turbojet-
component performance by means of model processes.
Progress in the description of turbine performance by means
of model processes is reported in reference 2.
An analysis in which the dimensions of the components are
related to the performance of a turbojet engine was made at
the NACA Lewis laboratory during 1948 and is presented
herein. The results are presented in such a fashion that
they are applicable to any turbojet engine. This general
presentation requires a knowledge of the efficiencies of the
individual components, compressor and turbine, under
various operating conditions. The performance of turbojet
engines for constant efficiencies of compressor and turbine
may be read directly from the general presentation. Super-
imposition of compressor and turbine characteristics upon
the general presentation permits accurate calculation of the
performance. Results of the analysis are compared with
This analysis is of interest for three reasons:
(1) It is a step toward a rational calculation of turbojet-
engine performance, the full realization of which will permit
calculation of performance from the drawings of the engine.
(2) The generalized presentation shows how variations in
important design and operating parameters will influence
(3) The analysis affords a method of accurately matching
compressors and turbines for which the performance char-
acteristics are known in detail.
The following symbols are used in this report:
A cross-sectional area, square feet
A5 turbine minimum-passage area, square feet
a velocity of sound based on total temperature, feet
D compressor-rotor-blade-tip diameter, feet
F net thrust, pounds
f fuel-air ratio plus 1
K ratio of inlet-air velocity to compressor-blade-tip
-.1 compressor-blade-tip "Mach number based on inlet
M1.o compressor-blade-tip MIach number based on ambi-
0 flight.. Mach number based on ambient temperature
N engine speed, rpm
P total pressure, potmnds per square foot absolute
p static pressure, pounds per square foot absolute
Q air flow, cubic feet per second
R gas constant, foot-poumds per slug OR
r total-pressure ratio
T total temperature, OR
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Sanders, John C. & Chapin, Edward C. Equilibrium Operating Performance of Axial-Flow Turbojet Engines by Means of Idealized Analysis, report, February 25, 1949; (digital.library.unt.edu/ark:/67531/metadc60326/m1/1/: accessed December 16, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.