Investigation of turbines suitable for use in a turbojet engine with high compressor pressure ratio and low compressor-tip speed 6: experimental performance of two-stage turbine Page: 3 of 29
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NACA RM E56E04
diagrams for the turbine requirements imposed by engine operation with
constant exhaust-nozzle area (ref. 2) and engine operation at constant
design rotative speed (ref. 3). Based on the analyses presented in ref-
erences 1 to 3, a turbine-outlet annular area of 405 square inches was
specified for engine operations with constant exhaust-nozzle area and
550 square inches for engine operation at constant design rotative speed.
Because the turbine design requirements for engine operation at
constant design rotative speed were more critical than those for engine
operation with constant exhaust-nozzle area, it was necessary to incor-U
porate a downstream stator behind a two-stage turbine in order to obtain
reasonable velocity diagrams. These velocity diagrams and those for the
two-stage turbine of reference 2 had higher Mach numbers, greater turn-
ing within blade rows, atd lower static-pressure drops across some of the
blade rows than those used in conventional turbine designs. Less criti-
cal turbine aerodynamic designs could, of course, have been obtained with
three-stage turbines or by increasing the design rotative speed, as dis-
cussed in reference 4.
Although the two-stage turbine design for engine operation with con-
stant exhaust-nozzle area and the two-stage turbine design with a down-
stream stator for engine operation at constant design rotative speed were
critical, achievement of reasonably good turbine performance appeared to
be feasible. However, only an experimental demonstration can verify this;
therefore, a two-stage turbine and a two-stage turbine with a downstream
stator were fabricated and investigated as components with cold-air
turbine-inlet conditions. The performance of the two-stage turbine with
a downstream stator is presented in reference 5. At equivalent design
work and speed the brake internal efficiency of this turbine was 0.81,
and the maximum efficiency obtained was 0.85. The downstream stator left
very little energy in the form of tangential velocity in the gas and, in
general, performed well with 0.78 recovery being obtained at equivalent
design work and speed. The poor over-all performance of this turbine was
attributed in part to the blade design procedure used, which appeared to
be inadequate for a turbine with such critical aerodynamic limits. In
addition, secondary-flow and tip-clearance effects that could not be ac-
counted for in design may have contributed to the poor performance. The
purpose of the subject report is to present and discuss the performance
of the two-stage turbine.
The two-stage turbine was operated at a constant inlet total (stag-
nation) pressure of 35 inches of mercury absolute and an inlet total tem-
perature of 7000 R. Over-all turbine performance characteristics were
obtained over a range of pressure ratios and speeds. These performance
results are presented in terms of brake internal efficiency, equivalent
work output, equivalent weight flow, and eq ivalent rotor speed.
In addition to the over-all performance, radial surveys of total
pressure and.flow abgle were made behind each blade row and ahead of the
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Davison, Elmer H.; Schum, Harold J. & Petrash, Donald A. Investigation of turbines suitable for use in a turbojet engine with high compressor pressure ratio and low compressor-tip speed 6: experimental performance of two-stage turbine, report, August 20, 1956; (https://digital.library.unt.edu/ark:/67531/metadc62779/m1/3/: accessed March 28, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.