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Most modern passenger and military aircraft are powered by
gas turbine engines, which are also called
jet engines. There are several different types
of gas turbine engines, but all turbine engines have some parts
in common. All gas turbine engines have a power turbine
located downstream of the burner to extract
energy from the hot flow and turn the
is done on the
power turbine by the hot exhaust flow from the burner.
Description of Images
The bottom of the figure shows:
- computer drawings of a turbojet
with the location of the turbine relative to the other engine
components, on the right
- the turbine section alone with the central shaft attached to
the turbine, on the left.
In both drawings, the turbine is magenta in color and
the shaft is colored blue. The left
end of the shaft would be attached to
which is colored cyan in the drawing on the right.
Here is an animated version of the turbine section:
The upper left of the figure shows an actual power turbine.
The turbine, like the compressor, is composed of several rows of
airfoil cascades. Some of the rows, called rotors, are
connected to the central shaft and rotate
at high speed. Other rows, called stators, are fixed and do
not rotate. The job of the stators is to keep the flow from spiraling
around the axis by bringing the flow back parallel to the axis.
Depending on the engine type, there may
be multiple turbine stages present in the engine. Turbofan
and turboprop engines usually employ a
separate turbine and shaft to power the fan and gear box
respectively. Such an arrangement is termed a two spool
engine. For some high performance engines, an additional turbine and
shaft is present to power separate parts of the compressor. This
arrangement produces a three spool engine. The power turbine
shown on the upper left of the figure is for a two spool, turbofan
There are several interesting turbine design details present on
this slide. Since the turbine extracts energy from the flow, the
across the turbine. The pressure gradient helps keep the
to the surface of the turbine blades. Since the boundary
layer is less likely to separate on a turbine blade
than on a compressor blade,
the pressure drop across a single turbine stage
can be much greater than the pressure increase
across a corresponding compressor stage. A single turbine stage can
be used to drive multiple compressor stages.
Because of the high pressure change across the turbine,
the flow tends to leak around the tips of the blades.
The tips of turbine blades are often connected by a thin
metal band to keep the flow from leaking,
as shown in the picture at the upper left.
Turbine blades exist in a much more hostile environment than
compressor blades. Sitting just downstream of the burner, the blades
experience flow temperatures of more than a thousand degrees
Fahrenheit. Turbine blades must be made of special
materials that can withstand the heat, or they must be actively cooled.
upper right of the figure, we show a picture of a single, actively
cooled turbine blade. The blade is hollow and cool air, which is
bled off the compressor, is pumped through the blade and out through
the small holes on the surface to keep the surface cool.
Parts of a Jet Engine:
- Beginner's Guide Home Page