Research Papers

Improving Turbine Stage Efficiency and Sealing Effectiveness Through Modifications of the Rim Seal Geometry

[+] Author and Article Information
Ivan Popovíc

e-mail: ivan.popovic@cantab.net

Howard P. Hodson

Whittle Laboratory,
University of Cambridge,
Cambridge, UK

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in JOURNAL OF TURBOMACHINERY. Manuscript received April 30, 2012; final manuscript received June 1, 2013; published online September 13, 2013. Editor: David Wisler.

J. Turbomach 135(6), 061016 (Sep 13, 2013) (10 pages) Paper No: TURBO-12-1041; doi: 10.1115/1.4024872 History: Received April 30, 2012; Revised June 01, 2013

This paper presents an investigation of a range of engine realistic rim seals starting from a simple axial seal to different types of overlapping seals. The experiments were performed in a large-scale linear cascade equipped with a secondary air system capable of varying independently both the mass fraction as well as the swirl velocity of the leakage air. The experimental results were also complemented by computationally fluid dynamics (CFD) to provide better insight in the flow physics. It has been found that the key feature of the rim seals that affect their impact on overall loss generation and their ability to provide good sealing effectiveness was the location and the size of the recirculation zones within the rim seal. The requirements for good sealing and reduced spoiling effects on the main gaspath flow often led to contradictory designs. In general, the recirculation zones were found to improve sealing by reducing the effect of the pitchwise (circumferential) variation in the pressure distribution due to the blade's potential field, and thus reduce ingestion. However, at the same time the recirculation zones tend to increase the loss generation. The best compromise was found when the outer part of the seal and its interface with the rotor platform was as smooth as possible to minimize the spoiling losses, while the recirculation zones were confined to the inner part of the seal to maintain acceptable levels of sealing effectiveness. A new rim seal design, which utilizes the best attributes of the above mentioned designs was developed. Linear cascade tests showed the losses due to the leakage-mainstream interaction were reduced by 33% compared to the datum seal design. Further validation was performed by examining the new configuration using unsteady full-stage calculations under engine realistic conditions. These calculations suggest an improvement of nearly 0.2% in the stage efficiency.

Copyright © 2013 by ASME
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Fig. 1

Cascade and secondary air injector

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Fig. 2

Plane for calculation of sealing effectiveness

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Fig. 3

Computational mesh

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Fig. 4

Rim seal geometries

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Fig. 5

Overall seal performance in terms of losses and sealing effectiveness for configurations C2, C3.1, and C4.1

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Fig. 6

Isosurface of fluid temperature slightly below mainstream air temperature at LF = 1.0%

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Fig. 7

Effects of rim seal geometry on adiabatic cooling effectiveness at a fixed leakage fraction of 1.0%

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Fig. 12

Calculated effects of outer recirculation zone on the overall seal performance

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Fig. 8

Experimentally measured total pressure contours coefficient (CPO) and normalized streamwise vorticity (Cωs) at a plane 50% Cx downstream of blade row at LF = 1.0%

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Fig. 9

Measured effects of internal recirculation zone on the overall seal performance

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Fig. 10

Rim seal aerothermodynamics midpitch meridional plane at LF = 0.75% for C3.1 and C3.2

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Fig. 11

Rim seal aerothermodynamics midpitch meridional plane at LF = 1.0% for C4.1 and C4.2

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Fig. 13

Predicted improvements in the overall performance by means of superpositioning

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Fig. 15

Performance of the best performing rim seals

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Fig. 16

End wall aerodynamics at LF = 1.0%

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Fig. 14

Predicted effects of rim seal–rotor platform blending with and without annulus step

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Fig. 17

Pitchwise averaged yaw angles at the plane 50%Cx downstream of the blade row—experimental results

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Fig. 18

Numerical validation using the unsteady full-stage calculations: time-averaged sealing effectiveness and efficiency drop relative to the baseline



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