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Research Papers

Optimized Shroud Design for Axial Turbine Aerodynamic Performance

[+] Author and Article Information
L. Porreca1

Turbomachinery Laboratory, Swiss Federal Institute of Technology, CH-8092 Zurich, Switzerlandluca.porreca@ch.manturbo.com

A. I. Kalfas2

Turbomachinery Laboratory, Swiss Federal Institute of Technology, CH-8092 Zurich, Switzerland

R. S. Abhari

Turbomachinery Laboratory, Swiss Federal Institute of Technology, CH-8092 Zurich, Switzerland

1

Present address: MAN Turbo AG Schweiz, Zurich, Switzerland.

2

Present address: Aristotle University of Thessaloniki, Thessaloniki, Greece.

J. Turbomach 130(3), 031016 (May 05, 2008) (12 pages) doi:10.1115/1.2777187 History: Received February 12, 2007; Revised March 06, 2007; Published May 05, 2008

This paper presents a comprehensive study of the effect of shroud design in axial turbine aerodynamics. Experimental measurements and numerical simulations have been conducted on three different test cases with identical blade geometry and tip clearances but different shroud designs. The first and second test cases are representative of a full shroud and a nonaxisymmetric partial shroud geometry while the third test case uses an optimized partial shroud. Partial shrouds are sometimes used in industrial application in order to benefit from the advantage of shrouded configuration, as well as reduce mechanical stress on the blades. However, the optimal compromise between mechanical considerations and aerodynamic performances is still an open issue due to the resulting highly three-dimensional unsteady flow field. Aerodynamic performance is measured in a low-speed axial turbine facility and shows that there are clear differences between the test cases. In addition, steady and time resolved measurements are performed together with computational analysis in order to improve the understanding of the effect of the shroud geometry on the flow field and to quantify the sources of the resultant additional losses. The flow field analysis shows that the effect of the shroud geometry is significant from 60% blade height span to the tip. Tip leakage vortex in the first rotor is originated in the partial shroud test cases while the full shroud case presents only a weak indigenous tip passage vortex. This results in a significant difference in the secondary flow development in the following second stator with associated losses that varies by about 1% in this row. The analysis shows that the modified partial shroud design has improved considerably the aerodynamic efficiency by about 0.6% by keeping almost unchanged the overall weight of this component, and thus blade root stresses. The work, therefore, presents a comprehensive flow field analysis and shows the impact of the shroud geometry in the aerodynamic performance.

Copyright © 2008 by American Society of Mechanical Engineers
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References

Figures

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Figure 4

Mass-averaged absolute yaw angle at the exit of the first rotor (Plane A1): expt. data (left), and expt. and CFD data of the EPS case (right)

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Figure 5

Mass-averaged relative total pressure coefficient at the exit of the first rotor (Plane A1): expt. data (left), and expt. and CFD data of the EPS case (right)

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Figure 6

Measured relative total pressure coefficient at the exit of the first rotor at one blade passing position (Plane A1)

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Figure 7

Measured time-distance diagram of relative total pressure coefficient at 80% blade span at the exit of the first rotor (Plane A1)

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Figure 8

Mass-averaged yaw angle at the exit of the second stator (Plane A2) expt. data (left), and expt. and CFD data of the EPS case (right)

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Figure 9

Mass-averaged total pressure coefficient at the exit of the second stator (Plane A2): expt. data (left), and expt. and CFD data of the EPS case (right)

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Figure 10

Measured total pressure coefficient and secondary flow vector plot at the exit of the second stator FS* (top), PS* (middle), and EPS (bottom) (Plane A2) (data marked with asterisk are from Porreca (9))

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Figure 11

Calculated streamlines and entropy function on the second stator suction surface: FS (top), PS (middle), and EPS (bottom)

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Figure 12

Calculated area-averaged meridional entropy function: FS (top), PS (middle), and EPS (bottom) test cases

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Figure 13

Mass-averaged yaw angle at the turbine exit (Plane A3): expt. data (left), and expt. and CFD data of the EPS case (right)

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Figure 14

Calculated streamline evolution at the turbine exit region (second rotor). Colors indicate entropy level.

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Figure 15

Entropy generation rate in different regions of the second rotor blade row as a percentage of the total entropy production in the second stage

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Figure 16

Measured total to total second stage efficiency in the FS, PS, and EPS test cases

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Figure 3

Details of the numerical mesh on the shroud location: FS (left), PS (middle), and EPS (right)

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Figure 2

Schematic of the shroud geometry: FS (left), PS (middle), and EPS (right)

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Figure 1

Meridional view of the two-stage geometry and the shroud different configurations

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