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Research Papers: Gas Turbines: Turbomachinery

A Comparison of Single and Double Lip Rim Seal Geometries

[+] Author and Article Information
Svilen S. Savov

Whittle Laboratory,
Department of Engineering,
University of Cambridge,
Cambridge CB3 0DY, UK
e-mail: sss44@cam.ac.uk

Nicholas R. Atkins

Whittle Laboratory,
Department of Engineering,
University of Cambridge,
Cambridge CB3 0DY, UK
e-mail: nra27@cam.ac.uk

Sumiu Uchida

Technology and Innovation HQ,
Mitsubishi Heavy Industries Ltd.,
5-717-1 Fukahori-machi,
Nagasaki 851-0392, Japan
e-mail: sumiu_uchida@mhi.co.jp

Contributed by the Turbomachinery Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received November 24, 2016; final manuscript received May 3, 2017; published online July 19, 2017. Editor: David Wisler.

J. Eng. Gas Turbines Power 139(11), 112601 (Jul 19, 2017) (13 pages) Paper No: GTP-16-1545; doi: 10.1115/1.4037027 History: Received November 24, 2016; Revised May 03, 2017

The effect of the purge flow, engine-like blade pressure field, and mainstream flow coefficient are studied experimentally for a single and double lip rim seal. Compared to the single lip, the double lip seal requires less purge flow for similar levels of cavity seal effectiveness. Unlike the double lip seal, the single lip seal is sensitive to overall Reynolds number, the addition of a simulated blade pressure field, and large-scale nonuniform ingestion. In the case of both seals, unsteady pressure variations attributed to shear layer interaction between the mainstream and rim seal flows appear to be important for ingestion at off-design flow coefficients. The double lip seal has both a weaker vane pressure field in the rim seal cavity and a smaller difference in seal effectiveness across the lower lip than the single lip seal. As a result, the double lip seal is less sensitive in the rotor–stator cavity to changes in shear layer interaction and the effects of large-scale circumferentially nonuniform ingestion. However, the reduced flow rate through the double lip seal means that the outer lip has increased sensitivity to shear layer interactions. Overall, it is shown that seal performance is driven by both the vane/blade pressure field and the gradient in seal effectiveness across the inner lip. This implies that accurate representation of both, the pressure field and the mixing due to shear layer interaction, would be necessary for more reliable modeling.

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References

Figures

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Fig. 1

Test rig schematic and potential ingress/egress patterns

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Fig. 2

(a) CP from steady RANS CFD at measured rig boundary conditions and Mis = 0.64 compared to measurements at both Mis = 0.64 and 0.2. Data are located on the hub line, 0.02cx downstream of the vane trailing edge. Steady RANS CFD results with engine geometry and boundary conditions are shown for comparison. (b) Comparison of CP,rel from steady RANS CFD between the engine and stubby blade just downstream of the mixing plane at a radial height of 40% rig span, 12.5% span on the engine vane.

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Fig. 3

Sectional views of single lip and double lip seals. Not to scale.

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Fig. 4

Table of experimental studies performed on the single lip and double lip seals

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Fig. 5

Schematic illustration of sealing parameter, Φ, and mainstream flow coefficient, ϕ

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Fig. 6

εc versus Φ curves for the single lip and double lip seals at high and low Re conditions with and without blades, at an engine-matched mainstream flow coefficient. Double lip seal measurements without mainstream flow are also plotted.

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Fig. 7

Unbladed single lip seal: normalized pressure, P¯, and seal effectiveness, εc, across two vane pitches in the rim seal and rotor–stator cavities across three values of Φ

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Fig. 8

Unbladed double lip seal: normalized pressure, P¯, and seal effectiveness, εc, across two vane pitches in the rim seal and rotor–stator cavities across three values of Φ

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Fig. 9

Vane pressure field peak-to-peak pressures for the single lip and double lip seals bladed and unbladed at the high Re condition

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Fig. 10

Difference in εc across the single lip and double lip seals plotted against Φ and against cavity εc

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Fig. 11

Radial seal effectiveness profile in the rim seal cavity for the single lip seal

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Fig. 12

Unbladed configuration of single lip seal at the high Re condition: circumferential εc for three values of Φ labeled (a), (b), and (c) and eccentricity, e, measurements relative to seal clearance, sc

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Fig. 13

(a) Schematic representation of likely nonuniform ingestion pattern into the rotor–stator cavity. (b) Radial εc profiles at location a–a for unbladed single lip seal showing a radial increase in εc. (c) A radial increase in seal effectiveness from literature. Replotted from Sangan et al. [45]. (a) Hypothesized flow path along stator boundary layer, (b) radial εc measurements (section a–a), and (c) in literature.

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Fig. 14

Unbladed configuration of double lip seal at the high Re condition: circumferential εc ∼ 0.8

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Fig. 15

Spectrograms of the unsteady pressure in the rim seal cavity for the single lip seal with and without rotor blades at Reθ = 4.9 × 106 and Rex = 2.3 × 106. The spectrograms are plotted for three levels of cavity εc, a, b, c. Note: ΔPseal is taken at a cavity εc of 0.875.

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Fig. 16

Spectrograms of the unsteady pressure in the rim seal cavity for the double lip seal with and without rotor blades at Reθ = 4.9 × 106 and Rex = 2.3 × 106. The spectrograms are plotted for three levels of cavity εc, a, b, c. Note: ΔPseal is taken at a cavity εc of 0.925.

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Fig. 17

Single lip seal, bladed configuration at Reθ = 4.9 × 106, Rex = 2.3 × 106, and cavity εc ∼ 0.9: spectrograms of the unsteady pressure signal at three radial locations (rim seal, rotor–stator cavity, and purge feed cavity) over 60 disk revolutions

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Fig. 18

Comparison of steady and unsteady pressures for the single lip (a) and double lip (b) seals, Reθ = 4.9 × 106, Rex = 2.3 × 106

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Fig. 19

Single lip seal. Top: spectrograms of unsteady pressure signal in the rim seal cavity at the three disk speeds corresponding to a, b, and c. Bottom: variation in seal effectiveness, εc, with disk speed normalized by mainstream velocity at three radial locations.

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Fig. 20

Double lip seal. Top: spectrograms of unsteady pressure signal in the rim seal cavity at three disk speeds. Bottom: variation in seal effectiveness, εc, with disk speed normalized by mainstream velocity at three radial locations.

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Fig. 21

Effect of disk speed on relative flow velocity at the rim seal cavity

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