engines are well suited for a higher range of specific speeds and
work at relatively high efficiency.
The axialflow turbine consists of two main elements, a set of
stationary vanes followed by a turbine rotor. Axialflow turbines
may be of the singlerotor or multiplerotor type. A stage consists
of two main components: a turbine nozzle and a turbine rotor or
wheel, as shown in figure 1.21. Turbine blades are of two basic
types, the impulse and the reaction. Modern aircraft gas turbines
use blades that have both impulse and reaction sections, as shown in
figure 1.23.
Figure 1.23. ImpulseReaction Turbine Blade.
The stationary part of the turbine assembly consists of a row
of contoured vanes set at a predetermined angle to form a series of
small nozzles which direct the gases onto the blades of the turbine
rotor. For this reason, the stationary vane assembly is usually
called the turbine nozzle, and the vanes are called nozzle guide
vanes.
b. Singlerotor turbine. Some gas turbine engines use a
singlerotor turbine, with the power developed by one rotor. This
arrangement is used on engines where low weight and compactness are
necessary. A singlerotor, singlestage turbine engine is shown in
figure 1.24, and a multiplerotor, multiplestage turbine engine is
shown in figure 1.25.
c. Multiplerotor turbine. In the multiplerotor turbine the
power is developed by two or more rotors. As a general rule,
multiplerotor turbines increase the total power generated in a unit
of small diameter. Generally the turbines used in Army aircraft
engines have multiple rotors. Figure 1.26 illustrates a multistage,
multiplerotor turbine assembly.
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