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Research Papers

Analysis of the Variable Geometry Effect in Radial Turbines

[+] Author and Article Information
Nicolas Binder1

Institut Supérieur de l'Aéronautique et de l'Espace (ISAE), Université de Toulouse, 10 Avenue Edouard Belin, BP 54032, 31055 Toulouse Cedex 4, Francenicolas.binder@isae.fr

Sebastien Le Guyader

Institut Supérieur de l'Aéronautique et de l'Espace (ISAE), Université de Toulouse, 10 Avenue Edouard Belin, BP 54032, 31055 Toulouse Cedex 4, Francesebastien.leguyader@isae.fr

Xavier Carbonneau

Institut Supérieur de l'Aéronautique et de l'Espace (ISAE), Université de Toulouse, 10 Avenue Edouard Belin, BP 54032, 31055 Toulouse Cedex 4, Francexavier.carbonneau@isae.fr

1

Corresponding author.

J. Turbomach 134(4), 041017 (Jul 21, 2011) (9 pages) doi:10.1115/1.4003713 History: Received April 02, 2010; Revised February 07, 2011; Published July 21, 2011; Online July 21, 2011

The influence of variable geometry stators on the stage behavior is analyzed from both theoretical and experimental points of view. A theoretical analysis of the trajectory of some pressure-ratio lines in a loading-to-flow-coefficient diagram leads to the definition of a specific dimensionless parameter: the reduced section. This parameter is representative of the stator geometric configuration and is thus expected to be a good candidate to describe the variable geometry problem. From a theoretical point of view, this parameter is no less than the formal expression of the link between the geometric configuration of the stator and the behavior of the stage. An experimental approach decomposed in three phases is then led to evaluate this assessment. The results clearly demonstrate the crucial influence of the reduced section in the operating point definition. It leads to the conclusion that from a theoretical point of view, the two solutions mainly used in the industry for variable geometry stages (variation of the height or of the opening position of the stator blades) are equivalent provided that they are sanitized of their respective technological drawbacks. It has also been shown that the geometric configuration of the stator chosen to reach a specific value of the reduced section has some incidence on the efficiency of the stage. This observation gives some opportunities for optimization, for which some axis of reflection is given.

Copyright © 2012 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Pressure-ratio line evolution in a ψ−ϕ map

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Figure 2

Geometric factors of the stator

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Figure 3

Geometries for which a bad guiding of the flow is expected

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Figure 4

ψ−ϕ map at πts=1.8 for all the opening positions of the reference stator

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Figure 5

ψ−ϕ map at πts=1.8 for some combined variations of stator opening position and stator height

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Figure 6

Variation of the pressure-ratio line’s slope with the value of S3∗

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Figure 7

Superposition of the map for both high and small stator heights. Numerical values are relative to the reference state.

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Figure 8

Mass-flow and rotational speed evolution against the reduced section for πts=1.8

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Figure 9

Equivalence in the ψ−ϕ map of initial and modified configurations for πts=1.8

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Figure 10

Pressure-ratio line’s slope of the modified configurations

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Figure 11

Reproduction of the variable geometry behavior without opening-configuration modification

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Figure 12

Efficiency evolution with the mass-flow for πts=1.8

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Figure 13

ψ−ϕ map at πts=1.8 for the different geometries having the same reduced section value (3a,…,3d)

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Figure 14

Mass-flow and rotational speed evolutions against the pressure-ratio value

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Figure 15

Efficiency evolution against the reduced tip-speed

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Figure 16

Efficiency evolution against the free space parameter

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