Research Papers: Gas Turbines: Structures and Dynamics

Use of Pressure Measurements to Determine Effectiveness of Turbine Rim Seals

[+] Author and Article Information
J. Michael Owen, James A. Scobie, GeonHwan Cho, Gary D. Lock

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

Kang Wu

Department of Thermal Engineering,
Tsinghua University,
Beijing 100084, China

Carl M. Sangan

Department of Mechanical Engineering,
University of Bath,
Bath BA2 7AY, UK
e-mail: c.m.sangan@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 21, 2014; final manuscript received July 28, 2014; published online October 7, 2014. Editor: David Wisler.

J. Eng. Gas Turbines Power 137(3), 032510 (Oct 07, 2014) (10 pages) Paper No: GTP-14-1417; doi: 10.1115/1.4028395 History: Received July 21, 2014; Revised July 28, 2014

The ingress of hot gas through the rim seal of a gas turbine depends on the pressure difference between the mainstream flow in the turbine annulus and that in the wheel-space radially inward of the rim seal. In this paper, a previously published orifice model is modified so that the sealing effectiveness εc determined from concentration measurements in a rig could be used to determine εp, the effectiveness determined from pressure measurements in an engine. It is assumed that there is a hypothetical “sweet spot” on the vane platform where the measured pressures would ensure that the calculated value of εp equals εc, the value determined from concentration measurements. Experimental measurements for a radial-clearance seal show that, as predicted, the hypothetical pressure difference at the sweet spot is linearly related to the pressure difference measured at an arbitrary location on the vane platform. There is good agreement between the values of εp determined using the theoretical model and values of εc determined from concentration measurements. Supporting computations, using a 3D steady computational fluid dynamics (CFD) code, show that the axial location of the sweet spot is very close to the upstream edge of the seal clearance. It is shown how parameters obtained from measurements of pressure and concentration in a rig could, in principle, be used to calculate the sealing effectiveness in an engine.

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Fig. 1

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

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Fig. 2

Rig test section with inset highlighting the static pressure taps in the vane hub (location A) and typical pressure asymmetry in the annulus. (Red indicates the stationary disk and blue indicates the rotating disk.)

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Fig. 3

Typical circumferential variation of pressure coefficient at location A in the annulus. CF = 0.538, Reϕ = 8.17 × 105, and Φ0 = 0. (Symbols denote experimental measurements and curve shows computed variation.)

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Fig. 4

Schematic of radial-clearance seal and annulus showing location A. Static dimensions in mm: h = 10; S = 20; sc,ax = 2.00; sc,rad = 1.28; and soverlap = 1.86.

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Fig. 5

Comparison between theoretical and measured values of εc for radial-clearance seal

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Fig. 6

Effect of Φomin on computed variation of g∧ and g with x showing location of sweet spot. (Horizontal broken lines show values of g∧; solid curve shows computed variation of g(x); and solid vertical line shows mean value of computed x∧.)

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Fig. 7

Computed variation of x∧ with Φomin. (Solid line shows mean value of x∧, with its geometric position shown in relation to the seal clearance (inset).)

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Fig. 8

Effect of r1/b on measured variation of g(xA) with Φo/Φmin

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Fig. 9

Variation of g∧ with measured values of g(xA). (Solid line shows linear regression of data.)

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Fig. 10

Variation of g∧ and g (xA) with Φomin

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Fig. 11

Variation of sealing effectiveness with Φomin. (Solid symbols denote values of εp from pressure measurements; open symbols denote values of εc from concentration measurements; and solid curve is based on effectiveness equation.)




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