Summary of Investigations of Mark 25 Aerial-Torpedo Turbine Page: 3 of 25
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NACA RM SE5OD2
somewhat with different nozzles, no specific trend of efficiency
with nozzle size or shape within the range investigated could be
established. Increasing the blade height from 0.35 to 0.45 inch
resulted in an increase of blade efficiency from 0.47 to 0.54 a't
design conditions with nozzle H. The effect on the performance of
the single-stage turbine of changing the blade-inlet angle from
170to 200 was negligible.
Consideration of the losses affecting the turbine performance
indicated that any further improvement must originate from decreasing
the following losses: (a) leaving losses that could be partly recov-
ered by either a more effective second stage or by a suitably designed
stator row and diffuser; and (b) losses resulting from large turning
of supersonic flow, which might be decreased by an improved blade-
Torpedoes operating on a combustion cycle require a high-
pressure-ratio low-speed gas turbine to drive the propellers of
the unit. Some types of rocket require similar turbines to power
the fuel or propellant pumps. Both applications involve the extrac-
tion of maximum power with minimum size and weight of power plant,
combustion constituents, and gearing. Because of the need for infor-
mation on turbines of this type, at the request of the Bureau of
Ordnance, Department of the Navy, an extensive investigation was
made at the NACA Lewis laboratory on the two-stage counterrotating
impulse turbine from the Mark 25 aerial torpedo.
Because of the aforementioned design requirements, this partic-
lar turbine had an 11-inch blade-tip diameter, a 900 are of admission,
small nozzle- and rotor-passage areas, supersonic-design velocities
relative to the first rotor, and counterrotation of the second rotor
to minimize gyroscopic effects. In a turbine of this size and type,
it is at present virtually impossible to predict the performance on
the basis of a sound design method. The investigation consisted
principally of the experimental determination of the performance both
of the standard turbine and of the turbine with modified components
inasmuch as detailed flow measurements within the turbine could not
be obtained with available methods. Among the variables investigated
were nozzle-passage size and shape, first-stage rotor-blade height
and inlet angle, and shrouding of the first-stage rotor. Also inves-
tigated were the division of work between the two stages, the effect
of axial nozzle-rotor clearance, and the magnitudes of such losses
as disk windage, rotor-blade pumping losses, and mechanical losses.
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Schum, Harold J.; Whitney, Warren J. & Buckner, Howard A., Jr. Summary of Investigations of Mark 25 Aerial-Torpedo Turbine, report, March 1, 1950; (digital.library.unt.edu/ark:/67531/metadc64214/m1/3/: accessed November 13, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.