blades. Some models of turboprop engines use as
section. It always has flanges to provide for the
front and rear bolting of the assembly to the
many as five turbine stages. You should remember
combustion chamber housing and the exhaust
that regardless of the number of wheels necessary
cone assembly, respectively. Figure 1-39 shows a
for driving engine parts, there is always a turbine
turbine casing.
nozzle in front of each wheel.
The occasional use of more than one turbine
EXHAUST SECTION
wheel is necessary in cases of heavy rotational
The exhaust section of the turbojet engine is
loads. Heavy loads that require multiple-stage
made up of several parts, each of which has its
turbine wheels often make it advantageous to
use multiple rotors. Shafts are bolted to the
individual functions. Although the parts have
appropriate turbine on one end and at the other
individual purposes, they also have one common
end to the unit requiring the rotative power.
function. They must direct the flow of hot gases
Typical of this situation are split compressors or
rearward in such a manner as to prevent
propellers, or a gas generator for helicopters, In
turbulence, while causing a high final or exit
velocity to the gases.
each of these situations, the turbine for each of
In performing the various functions, each of
the rotors may have one or more stages.
In the single-rotor turbine, shown in figure
the parts affects the flow of gases in different
1-23, the power is developed by one rotor. All
ways, as described in the following paragraphs.
The exhaust section is directly behind the
engine-driven parts are driven by this single wheel,
This arrangement uses engines where the need for
turbine section. It ends with the ejection of gas
low weight and compactness predominates. The
at the rear in the form of a high-velocity jet.
single-rotor turbine may be either single or
The parts of the exhaust section include the
multiple stage.
exhaust cone, tailpipe (if required), and the
In the multiple-rotor turbine, the power is
exhaust, or jet nozzle, Each of these parts is
developed by two or more rotors. It is possible
discussed individually so the exhaust section will
for each turbine rotor to drive a separate part of
be quite familiar to you.
the engine. For example, a triple-rotor turbine
The exhaust cone collects the exhaust gases
may be so arranged that the first turbine
discharged from the turbine assembly and
drives the rear half of the compressor and the
gradually converts them into a solid jet. During
accessories. The second turbine drives the front
this operation, the velocity of the gases will
half of the compressor, and the third turbine
decrease slightly, and the pressure will increase.
furnishes power to a propeller (fig. 1-38).
This is caused by the diverging passage between
The turbine rotor arrangement for a dual-
the outer duct and the inner cone. The annular
area between the two units increases rearward
rotor turbine, such as required for a split-spool
compressor, is similar to the arrangement in figure
(fig. 1-40).
1-38. The difference is in the use of the third
turbine for a propeller,
The remaining elements concerning the turbine
is the turbine casing or housing. The turbine
casing encloses the turbine wheel and the nozzle
vane assembly. It gives either direct or indirect
support to the stator elements of the turbine
Figure 1-40.-Exhaust collector and welded support status.
Figure 1-39.-Turbine casing assembly.
1-27
