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Research Papers: Gas Turbines: Structures and Dynamics

Design of an Improved Turbine Rim-Seal

[+] Author and Article Information
James A. Scobie

Department of Mechanical Engineering,
University of Bath,
Bath BA2 7AY, UK
e-mail: j.a.scobie@bath.ac.uk

Roy Teuber

Siemens Industrial Turbomachinery Ltd.,
Lincoln LN5 7FD, UK
e-mail: roy.teuber@web.de

Yan Sheng Li

Siemens Industrial Turbomachinery Ltd.,
Lincoln LN5 7FD, UK
e-mail: yansheng.li@siemens.com

Carl M. Sangan

Department of Mechanical Engineering,
University of Bath,
Bath BA2 7AY, UK
e-mail: c.m.sangan@bath.ac.uk

Michael Wilson

Department of Mechanical Engineering,
University of Bath,
Bath BA2 7AY, UK
e-mail: m.wilson@bath.ac.uk

Gary D. Lock

Department of Mechanical Engineering,
University of Bath,
Bath BA2 7AY, UK
e-mail: g.d.lock@bath.ac.uk

1Corresponding author.

Contributed by the Structures and Dynamics Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received July 13, 2015; final manuscript received July 16, 2015; published online September 1, 2015. Editor: David Wisler.

J. Eng. Gas Turbines Power 138(2), 022503 (Sep 01, 2015) (10 pages) Paper No: GTP-15-1266; doi: 10.1115/1.4031241 History: Received July 13, 2015

Rim seals are fitted in gas turbines at the periphery of the wheel-space formed between rotor disks and their adjacent casings. These seals, also called platform overlap seals, reduce the ingress of hot gases which can limit the life of highly stressed components in the engine. This paper describes the development of a new, patented rim-seal concept showing improved performance relative to a reference engine design, using unsteady Reynolds-averaged Navier–Stokes (URANS) computations of a turbine stage at engine conditions. The computational fluid dynamics (CFD) study was limited to a small number of purge-flow rates due to computational time and cost, and the computations were validated experimentally at a lower rotational Reynolds number and in conditions under incompressible flow. The new rim seal features a stator-side angel wing and two buffer cavities between outer and inner seals: the angel-wing promotes a counter-rotating vortex to reduce the effect of the ingress on the stator; the two buffer cavities are shown to attenuate the circumferential pressure asymmetries of the fluid ingested from the mainstream annulus. Rotor disk pumping is exploited to reduce the sealing flow rate required to prevent ingress, with the rotor boundary layer also providing protective cooling. Measurements of gas concentration and swirl ratio, determined from static and total pressure, were used to assess the performance of the new seal concept relative to a benchmark generic seal. The radial variation of concentration through the seal was measured in the experiments and these data captured the improvements due to the intermediate buffer cavities predicted by the CFD. This successful design approach is a potent combination of insight provided by computation, and the flexibility and expedience provided by experiment.

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References

Figures

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Fig. 1

(a) Typical high-pressure gas turbine stage and (b) detail of rim seal [4]

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Fig. 2

Rim-seal concepts investigated by CFD: (a) reference seal and (b) angel-wing seal

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Fig. 3

Nomenclature for angel-wing seal

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Fig. 8

Rig test section highlighting pressure instrumentation (red/background, stationary; blue/foreground, rotating; see online version for color)

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Fig. 4

CFD model: (a) model domain and (b) wheel-space mesh

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Fig. 5

Convergence behavior for the sealing effectiveness εcc at four rim-seal positions

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Fig. 6

Case of maximum ingress for improved seal design: (a) computed velocity stream lines; (b) contour plot with swirl ratio β—note, the swirl contours were limited to β = 1 despite β > 1 in the annulus; and (c) contour plot of sealing effectiveness εcc

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Fig. 7

Case of maximum egress for improved seal design; (a) computed velocity stream lines; (b) contour plot with swirl ratio β—note, the swirl contours were limited to β = 1 despite β > 1 in the annulus; and (c) contour plot of sealing effectiveness εcc

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Fig. 9

Evolution of rim seal design from reference seal to angel wing

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Fig. 10

(a) Reference rim seal; (b) angel-wing seal; and (c) close up of angel-wing seal showing a selection of the 15 radial measurement locations including two sampling taps within the angel-wing structure

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Fig. 11

Radial distribution of concentration effectiveness for reference and angel-wing seals at three sealing flow rates

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Fig. 12

Measured variation of concentration effectiveness with nondimensional sealing flow rate for angel-wing seal at four sampling points (symbols denote data; lines are theoretical curves)

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Fig. 13

Experimental variation of concentration effectiveness with nondimensional sealing flow rate for reference and angel-wing seals, tested at the range of conditions given in Table 1 (symbols denote data; lines are theoretical curves)

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Fig. 14

(a) Experimental variation of concentration effectiveness with nondimensional sealing flow rate for four seal configurations; (b): detail of highlighted region in (a)

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Fig. 15

Radial distribution of swirl ratio for reference and angel-wing seals at three sealant flow rates

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