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TECHNICAL PAPERS

Fluid Dynamics and Performance of Partially and Fully Shrouded Axial Turbines

[+] Author and Article Information
L. Porreca

T. Behr, J. Schlienger, A. I. Kalfas, R. S. Abhari

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

J. Ehrhard

ALSTOM Switzerland Ltd.

E. Janke

Rolls Royce Deutschland

J. Turbomach 127(4), 668-678 (Mar 01, 2004) (11 pages) doi:10.1115/1.2008972 History: Received October 01, 2003; Revised March 01, 2004

A unique comparative experimental and numerical investigation carried out on two test cases with shroud configurations, differing only in the labyrinth seal path, is presented in this paper. The blade geometry and tip clearance are identical in the two test cases. The geometries under investigation are representative of an axial turbine with a full and partial shroud, respectively. Global performance and flow field data were acquired and analyzed. Computational simulations were carried out to complement the investigation and to facilitate the analysis of the steady and unsteady flow measurements. A detailed comparison between the two test cases is presented in terms of flow field analysis and performance evaluation. The analysis focuses on the flow effects reflected on the overall performance in a multi-stage environment. Strong interaction between the cavity flow and the blade tip region of the rotor blades is observed up to the blade midspan. A marked effect of this interaction can be seen in the downstream second stator where different vortex structures are observed. Moreover, in the partial shroud test case, a strong tip leakage vortex is developed from the first rotor and transported through the downstream blade row. A measurable change in the second stage efficiency was observed between the two test cases. In low aspect ratio blades within a multi-stage environment, small changes in the cavity geometry can have a significant effect on the mainstream flow. The present analysis has shown that an integrated and matched blade-shroud aerodynamic design has to be adopted to reach optimal performances. The additional losses resulting from small variations of the sealing geometry could result in a gain of up to one point in the overall stage efficiency.

Copyright © 2005 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

“LISA” Two stages axial turbine facility

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Figure 2

Schematic of the shroud configuration: (a) partial shroud, (b) full shroud

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Figure 3

Turbine traversing probe planes

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Figure 4

Spatial discretization in the labyrinth path (a) partial shroud, (b) full shroud

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Figure 5

Mass averaged yaw angles at the exit of the first rotor–plane A1–(a) absolute, (b) relative

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Figure 6

Absolute mass averaged yaw angles from midspan up to the cavity at the exit of the first rotor–plane A1

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Figure 7

End wall static pressure coefficient over the first rotor outer casing

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Figure 8

Measured static pressure distribution on the second stator: (a) 75%, (b) 90% span

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Figure 9

(a) Mass flow distribution, (b) mass averaged pitch angle at exit of the first rotor–Plane A1

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Figure 10

Mass averaged total pressure coefficient at exit of the first rotor–Plane A1–(a) absolute, (b) relative

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Figure 11

Mass averaged (a) total pressure coefficient (b) yaw angle at the exit of the second stator—Plane A2

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Figure 12

Measured total pressure coefficient and secondary flow vector plot downstream of the second stator–Plane A2–(a) PS test case, (b) FS test case

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Figure 13

Measured entropy function downstream of the second stator—Plane A2—(a) PS test case (b) FS test case

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Figure 14

Experimental time-distance diagram of the mass-averaged absolute yaw angle at the exit of the first rotor in three blade passing period (PS test case)—Plane A1

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Figure 15

Experimental mass-averaged yaw angle variation in three blade passing period at the exit of the first rotor. (PS test case)–Plane A1—(a) minimum and maximum values and 5HP measurements (b) variation range.

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Figure 16

Experimental time dependent relative total pressure coefficient in one blade passing period at the exit of the first rotor (PS test case)—Plane A1

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Figure 17

Experimental mass averaged yaw angle variation in three blade passing period at the exit of the second stator (PS test case)—Plane A2—(a) minimum and maximum values and 5HP measurements, (b) variation range

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Figure 18

Frequency of occurrence of the measured unsteady absolute yaw angle at 5.5%, 15%, 36%, 52% and 90% span at the exit of the second stator (PS test case)—Plane A2. Symbols show the 5HP measurements.

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Figure 19

Measured spanwise efficiency change between FS and PS test case

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Figure 20

Measured loading coefficient variation across the second rotor in three blade passing periods—PS test case—(a) minimum and maximum values, (b) variation range

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Figure 21

Measured isentropic enthalpy drop across the second stage—PS test case

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