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Research Papers: Gas Turbines: Structures and Dynamics

Measured Comparison of Leakage and Rotordynamic Characteristics for a Slanted-Tooth and a Straight-Tooth Labyrinth Seal

[+] Author and Article Information
Naitik J. Mehta

Mechanical Engineer-Rotating Equipment,
Bechtel OG&C,
Houston, TX 77056
e-mail: nmehta1@bechtel.com

Dara W. Childs

The Leland T. Jordan Chair
of Mechanical Engineering,
Turbomachinery Laboratory,
Texas A&M University,
College Station, TX 77843
e-mail: dchilds@tamu.edu

Contributed by the Structures and Dynamics Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received July 31, 2013; final manuscript received August 16, 2013; published online October 21, 2013. Editor: David Wisler.

J. Eng. Gas Turbines Power 136(1), 012501 (Oct 21, 2013) (11 pages) Paper No: GTP-13-1286; doi: 10.1115/1.4025267 History: Received July 31, 2013; Revised August 16, 2013

Measured results are presented to compare rotordynamic coefficients and leakage of a slanted-tooth labyrinth seal and a straight-tooth labyrinth seal. Both seals had identical pitch, depth, and number of teeth. The teeth inclination angle of the teeth on the slanted-tooth labyrinth was 65 deg from the normal axis. Experiments were carried out at an inlet pressure of 70 bar-a (1015 psi-a), pressure ratios of 0.4, 0.5, and 0.6, rotor speeds of 10.2, 15.35, and 20.2 krpm, and a radial clearance of 0.2 mm (8 mils). One zero and two positive inlet preswirl ratios were used. The results show only minute difference in the rotordynamic coefficients between the two seals. The slanted-tooth labyrinth seal consistently leaked approximately 10% less at all conditions. Predictions were made using a one control volume bulk-flow model (1CVM) which was developed for a straight-tooth labyrinth seal design. 1CVM under-predicted the rotordynamic coefficients and the leakage.

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References

Figures

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Fig. 1

Seal tooth profile of the seals

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Fig. 2

Cross-sectional view of annular gas seal test stand (AGSTS) [14]

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Fig. 4

Detailed sectional drawings of the preswirl rings [14]

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Fig. 5

Preswirl measurement and preswirl ring [14]

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Fig. 6

Dimensions for the slanted-tooth labyrinth seal

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Fig. 7

Dimensions for the straight-tooth labyrinth seal

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Fig. 8

Horizontal stiffener

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Fig. 9

Vertical stiffener

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Fig. 10

Stator coordinate systems viewed from the NDE

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Fig. 11

Dynamic stiffness data for slanted-tooth labyrinth after subtracting the baseline data

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Fig. 12

Variation of Re(HXX) with the stator masses

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Fig. 13

Variation of Re(HYY) with the stator masses

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Fig. 14

Cross-coupled stiffness versus inlet preswirl ratio

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Fig. 15

Direct damping versus inlet preswirl

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Fig. 16

Reaction forces developed by a synchronously-precessing labyrinth seal

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Fig. 17

Effective damping versus inlet preswirl

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Fig. 18

Whirl frequency ratio for slanted-tooth labyrinth seal

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Fig. 19

Seal leakage versus inlet preswirl

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Fig. 20

Prediction versus measurements of k and C at 20.2 krpm and 0.5 PR

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Fig. 21

Prediction versus measurements for Ceff at 20.2 krpm and 0.5 PR

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Fig. 22

Prediction versus measurements of leakage rate (m·) at 20,200 rpm and 0.5 PR

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