Figure 1-22.--Twin-spool engine.
rotors. They are referred to as LP compressor and
turbine powers the GG and accessories. The PT
powers the ship's propeller through the reduction
turbine rotor and HP compressor and turbine
gear and shafting. Refer to figures 1-21 and 1-22
rotor (fig. 1-22). The LP compressor and turbine
as we discuss these turbines.
are connected by a shaft. The shaft runs through
the hollow shaft that connects the HP turbine to
the HP compressor. The starter drives the HP
Gas Generator Turbine
assembly during engine start. The PT functions
The turbine that drives the compressor of a
the same as in the split-shaft engine. A larger
GTE is located aft of the combustion chamber
volume of air can be handled as compared to a
outlet. The turbine consists of two basic elements,
single- or split-shaft engine. The increase in overall
the stator or nozzle, and the rotor. A cutaway
dimensions and complexity makes the engine less
view of a stator element is shown in figure 1-23;
desirable for ship's propulsion than the split-shaft
a rotor element is shown in figure 1-24.
engine, as this type of engine has more moving
parts.
TURBINE STATORS.--The stator element
of the turbine section is known by a variety of
TURBINE ASSEMBLIES
names. The most common are turbine nozzle
The GTEs are not normally classified by
vanes and turbine guide vanes. In this text,
turbine stators are usually referred to as nozzles.
turbine type. However, we will discuss turbines
The turbine nozzle vanes are located directly aft
now so you will have knowledge of their
of the combustion chambers and immediately
construction before we describe the General
forward of, and between, the turbine wheels.
Electric LM2500 GTE in the next chapter.
Turbine nozzles have a twofold function.
In theory, design, and operating
First, the nozzles prepare the mass flow for
characteristics, the turbines used in GTEs are
harnessing of power through the turbine rotor.
similar to those used in steam plants. The GTE
This occurs after the combustion chamber has
differs from the steam turbine chiefly in (1) the
introduced the heat energy into the mass airflow
type of blading material used, (2) the means
and delivered it evenly to the nozzles. The
provided for cooling the turbine shaft bearings,
stationary vanes of the turbine nozzles are
and (3) the lower ratio of blade length to wheel
contoured and set at a certain angle. The spaces
diameter.
between the vanes form several small nozzles that
The designations GG and PT are used to
discharge the gas as extremely high-speed jets. The
differentiate between the turbines. The GG
1-20
