Summary of Investigations of Mark 25 Aerial-Torpedo Turbine Page: 4 of 25
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NACA M SE5OD12
The results of these studies are given in references 1 to 8
and are summarized herein with a discussion of the source of the
losses affecting turbine performance.
APPARATUS AND PROCEDURE
Turbine. - The Mark 25 aerial-torpedo power plant is a two-
stage counterrotating impulse turbine, designed to operate at a
pressure ratio of 15 and a turbine speed of 18,000 rpm. The two
turbine rotors are geared to operate at the same rotative speeds but
in opposite directions. The shroud-band diameters of the forward
and rear turbine rotors are 11.00 and 11.32 inches, respectively;
the corresponding blade lengths are 0.40 and 0.55 inch. Pitch diam-
eter of both rotors was 10.48 inches. An axial clearance of
0.150 inch between the two rotors was maintained.
The turbine operates with nozzles that effect a 900 arc of gas
admission. Design specifications require the gas to expand through
the nozzles and to enter the forward turbine blades at supersonic
relative velocities. Because most of the gas-velocity energy is
absorbed by the forward turbine rotor, the flow leaving the first
stage and entering the second stage is subsonic for idealized flow.
The second-stage turbine rotor is designed for a small amount of
reaction. This rotor is included in the design primarily for elim-
inating gyroscopic action.
In order to obtain the single-stage data, the turbine was modi-
fied and investigated as a single-stage unit. A description of
the standard turbine and the modifications necessary to convert the
two-stage unit into a single-stage turbine are given in references 1
and 2, respectively.
Nozzles. - Eight nozzles were investigated in all. Alphabetical
notation of the nozzles was arbitrarily selected to distinguish the
various nozzle designs as supplied by the manufacturer. All nozzles
are described in references 1, 3, and 5. The different design vari-
ables of these nozzles are summarized in the following table:
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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/m1/4/: accessed November 14, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.