Most modern passenger and military aircraft are powered by
gas turbine engines, which are also called
jet engines. There are several different types
of jet engines, but all jet engines have some partsin
common. All jet engines have a compressor
to increase the pressure of the incoming air
before it enters the burner.
Compressor performance
has a large influence on total engine
performance.
There are two main types of compressors used in jet engines. The
compressor shown above is called a centrifugal compressor
because the flow through the compressor is turned perpendicular to
the axis of rotation.
The other type of compressor is an axial
compressor and is discussed on a separate slide. The very first
jet engines used centrifugal compressors, and they are still used on
small
turbojets and
turbo shaft
engines.
How does a centrifugal compressor work? The details are quite
complex because the blade geometries and the resulting flows are
three dimensional, unsteady, and can have important viscous
and compressibility effects. Each blade on the compressor
produces a pressure variation much like the airfoil
of a spinning propeller. But unlike a
propeller blade, the blades of a centrifugal compressor are close to
one another, which seriously alters the flow between the blades.
Centrifugal compressors also do
work
on the flow by turning, and
therefore accelerating, the flow radially. Compressor designers must
rely on wind tunnel testing and
sophisticated computational
models to determine the performance
of a centrifugal compressor. The performance is characterized by the
pressure ratio across the compressor CPR, the rotational speed of
the shaft necessary to produce the pressure increase, and an
efficiency factor that indicates how much additional work is required
relative to an ideal compressor.
Activities:
Guided Tours
-
Parts of a Jet Engine:
-
Compressor:
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