Editing Centrifugal compressor (section)

=== Centrifugal impeller ===

[[File:2 polys.png|thumb|upright= 1.35|Figure 1.2.1 - Graphic modeling of the impeller, similar to turbocharger impeller]]
The identifying component of a centrifugal compressor stage is the centrifugal impeller rotor. Impellers are designed in many configurations including "open" (visible blades), "covered or shrouded", "with splitters" (every other inducer removed), and "w/o splitters" (all full blades). Figures 1.1, 1.2.1, and 1.3  show three different open full inducer rotors with alternating full blades/vanes and shorter length splitter blades/vanes. Generally, the accepted mathematical nomenclature refers to the leading edge of the impeller with subscript 1. Correspondingly, the trailing edge of the impeller is referred to as subscript 2.

As working-gas/flow passes through the impeller from stations 1 to 2, the kinetic and potential energy increase. This is identical to an axial compressor with the exception that the gases can reach higher energy levels through the impeller's increasing radius. In many modern high-efficiency centrifugal compressors the gas exiting the impeller is traveling near the speed of sound.

Most modern high-efficiency impellers use "backsweep" in the blade shape.<ref name="Japikse">
{{cite book|author=Japikse, David
|title=Centrifugal Compressor Design and Performance
|year=1996
|publisher=Concepts ETI .
|isbn=978-0-933283-03-9}}
</ref><ref name="Whitfield, Baines">
{{cite book|author=Whitfield, A. |author2=Baines, N. C.
|title=Design of Radial Turbomachinery
|year=1990
|publisher=Longman Scientific and Technical
|isbn=978-0-470-21667-5}}</ref><ref name="Aungier">
{{cite book|author=Aungier, Ronald H.
|title=Centrifugal Compressors, A Strategy for Aerodynamic Design and Analysis
|publisher=ASME Press
|year=2000
|isbn=978-0-7918-0093-5}}</ref>

A derivation of the general [[Euler equations (fluid dynamics)]] is [[Euler's pump and turbine equation]], which plays an important role in understanding impeller performance. This equation can be written in the form:

Equation-1.2 (see Figures 1.2.2 and 1.2.3 illustrating impeller velocity triangles)

:<math>E=\left(\frac {u_2}{2g}-\frac {u_1}{2g}\right)+\left(\frac {w_2}{2g}-\frac {w_1}{2g}\right)+\left(\frac {c_2}{2g}-\frac {c_1}{2g}\right)</math>
where:
*{{mvar|1}} subscript 1 is the impeller leading edge (inlet), station 1
*{{mvar|2}} subscript 2 is the impeller trailing edge (discharge), station 2
*{{mvar|E}} is the [[energy]] added to the fluid
*{{mvar|g}} is the acceleration due to [[gravity]]
*{{mvar|u}} is the impeller's circumferential velocity, units [[velocity]]
*{{mvar|w}} is the velocity of flow relative to the impeller, units velocity
*{{mvar|c}} is the absolute velocity of flow relative to stationary, units velocity
<gallery>
Impeller inlet meridional triangles.PNG|Figuer1.2.2 -Inlet velocity triangles for centrifugal compressor impeller
Impeller exit meridional trianges.PNG|Figuer1.2.3 - Exit velocity triangles for centrifugal compressor impeller
</gallery>