The exit duct forms an envelope which changes the direction of the gas flow by providing an
outlet close to the compressor turbine guide vanes. The vanes ensure that the expanding gases are
directed to the compressor turbine blades at the proper angle to drive the compressor.
9.7.
TURBINE SECTION
The turbine rotor consists of two separate single-stage turbines located in the center of the
gas generator case and completely surrounded by the annular combustion chamber liner. The following
subparagraphs discuss the compressor and power turbines.
a.
The compressor turbine consists of a turbine disk, blades, and weights. The turbine
drives the compressor in a counterclockwise direction. The turbine assembly is splined to the
compressor front hub and secured by a threaded centerlocking turbine bolt and washer. A master spline
is provided to ensure that the disk assembly is always installed to a position to retain original balance.
The disk has a circumferential reference groove to enable checking disk growth. The 58 cast steel alloy
blades in the compressor turbine disk are secured in fir-tree serrations in the disk by individual tubular
rivets.
The compressor turbine is separated from the power turbine by an interstage baffle.
This baffle prevents dissipation of turbine gas and transmission of heat to turbine disk faces.
b.
The power turbine disk assembly, consisting of a turbine disk, blades, and weights,
drives the reduction gearing through the power turbine shaft in a clockwise direction. The power turbine
guide vanes are located ahead of the power turbine rotor in the gas stream. The vanes direct the flow of
gas at the most efficient angle to drive the power turbine. The power turbine disk is made to close
tolerances and has a circumferential reference groove to permit taking disk growth measurements when
required. A master spline insures that the turbine disk assembly is installed in a predetermined position
to retain the original balance. The required number of weights is determined during balancing
procedures and riveted to a special flange located on the rear of the turbine disk. The power turbine
blades differ from those of the compressor turbine in that they are cast with notched and shrouded tips.
The blades are secured by fir-tree serrations in the turbine disk. The blade tips rotate inside a double
knife-edge shroud and form a continuous seal when the engine is running. This reduces tip leakage and
increases turbine efficiency.
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