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Research Papers

Experimental Measurements of Ingestion Through Turbine Rim Seals—Part III: Single and Double Seals

[+] Author and Article Information
Gary D. Lock

Department of Mechanical Engineering,
University of Bath,
Bath BA2 7AY, UK

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received June 28, 2012; final manuscript received August 10, 2012; published online June 26, 2013. Editor: David Wisler.

J. Turbomach 135(5), 051011 (Jun 26, 2013) (11 pages) Paper No: TURBO-12-1088; doi: 10.1115/1.4007504 History: Received June 28, 2012; Revised August 10, 2012

This paper describes experimental results from a research facility, which experimentally models hot gas ingress into the wheel-space of an axial turbine stage. Measurements of CO2 gas concentration in the rim-seal region and inside the wheel-space are used to assess the performance of generic (though engine-representative) single and double seals in terms of the variation of concentration effectiveness with sealing flow rate. The variation of pressure in the turbine annulus, which governs externally induced ingress, was obtained from steady pressure measurements downstream of the vanes. The benefit of using double seals is demonstrated: the ingested gas is shown to be predominately confined to the outer wheel-space radially outward of the inner seal; and in the inner wheel-space, radially inward of the inner seal, the effectiveness is shown to be significantly higher. Criteria for ranking the performance of single and double seals are proposed, and the performance limit for any double seal is shown to be one in which the inner seal is exposed to rotationally induced ingress. Although the ingress is a consequence of an unsteady, three-dimensional flow field and the cause-effect relationship between pressure and the sealing effectiveness is complex, the experimental data is shown to be successfully calculated by simple effectiveness equations developed from a theoretical model. The data illustrate that, for similar turbine-stage velocity triangles, the effectiveness can be correlated using two empirical parameters. In principle, these correlations could be extrapolated to a geometrically similar turbine operating at engine-representative conditions.

Copyright © 2013 by ASME
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References

Figures

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Fig. 1

Generic rotor-stator turbine stage and double-seal inset

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Fig. 2

Simplified diagram of ingress and egress, showing boundary layers on the stator and rotor

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Fig. 3

Rig test section showing turbine stage

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Fig. 4

Circumferential distribution of Cp over nondimensional vane pitch at design condition: Rew / Reϕ = 0.538

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Fig. 5

Single seal configurations

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Fig. 6

Double seal configurations

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Fig. 7

Simplified diagram of double seal

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Fig. 8

Simplified diagram of ingress and egress for double axial-clearance seal, Φ0 < Φmin

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Fig. 9

Effect of sealing flow rate on measured radial variation of effectiveness on stator surface for single and double axial-clearance seals (S1 and D1). Open symbols denote D1; solid symbols denote S1.

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Fig. 10

Effect of sealing flow rate on measured radial variation of effectiveness on stator surface for single and double radial-clearance seals (S2c and D2). Open symbols denote D2; solid symbols denote S2c.

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Fig. 11

Comparison between theoretical effectiveness and experimental data for seal S1: EI and RI ingress (symbols denote data; lines are theoretical curves)

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Fig. 12

Variation of εc with Φo for single radial-clearance seals S2a, S2b, S2c: EI ingress (symbols denote data; lines are theoretical curves)

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Fig. 13

Variation of εc with Φo for single and double axial-clearance seals (S1 and D1): EI ingress (symbols denote data; lines are theoretical curves)

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Fig. 14

Variation of εc with Φo for single and double radial-clearance seals (S2b and D2): EI ingress (symbols denote data; lines are theoretical curves)

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Fig. 15

Comparison between theoretical effectiveness and εc,13 data for seals D1 and D2: EI and RI ingress (symbols denote data; lines are theoretical curves)

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Fig. 16

Seal performance ranking shown in order of magnitude of Φmin for all seal configurations

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