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Axial-flow
compressors are dynamic rotating compressors that
use arrays of fan-like aerofoils to progressively
compress the working fluid. They are used where
there is a requirement for a high flows or a compact
design.
The arrays of aerofoils are set in rows, usually as
pairs: one rotating and one stationary. The rotating
aerofoils, also known as blades or rotors,
decelerate and pressurise the fluid. The stationary
aerofoils, also known as a stators or vanes, turn
and decelerate the fluid; preparing and redirecting
the flow for the rotor blades of the next stage.
Axial compressors are almost always multi-staged,
with the cross-sectional area of the gas passage
diminishing along the compressor to maintain an
optimum axial Mach number. Beyond about 5 stages or
a 4:1 design pressure ratio, variable geometry is
normally used to improve operation.
Axial compressors can have high efficiencies; around
90% polytropic at their design conditions. However,
they are relatively expensive, requiring a large
number of components, tight tolerances and high
quality materials. Axial-flow compressors can be
found in medium to large gas turbine engines, in
natural gas pumping stations, and within certain
chemical plants. |
