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Research Papers

Leakage and Cavity Pressures in an Interlocking Labyrinth Gas Seal: Measurements Versus Predictions

[+] Author and Article Information
Luis San Andrés

Fellow ASME
Mast-Childs Chair Professor
Mechanical Engineering Department,
Texas A&M University,
College Station, TX 77843
e-mail: lsanandres@tamu.edu

Tingcheng Wu

Research & Development, Siemens,
500 Paul Clark Dr,
Olean, NY 14760
e-mail: wutingcheng29@gmail.com

Jose Barajas-Rivera

Mechanical Engineering Department,
Texas A&M University,
College Station, TX 77843
e-mail: jpb7678@tamu.edu

Jiaxin Zhang

Petroleum Engineering Department,
Texas A&M University,
College Station, TX 77843
e-mail: jiaxin.zhang2018@tamu.edu

Rimpei Kawashita

Mitsubishi Heavy Industries, Ltd.,
2 Chome-2-1-1 Araichō Shinhama,
Takasago-shi, Hyōgo-ken 676-8686, Japan
e-mail: rinpei_kawashita@mhi.co.jp

1Corresponding author.

Manuscript received June 25, 2019; final manuscript received June 25, 2019; published online August 2, 2019. Editor: Jerzy T. Sawicki.

J. Eng. Gas Turbines Power 141(10), 101007 (Aug 02, 2019) (9 pages) Paper No: GTP-19-1309; doi: 10.1115/1.4044284 History: Received June 25, 2019; Revised June 25, 2019

Gas labyrinth seals (LS) restrict secondary flows (leakage) in turbomachinery and their impact on the efficiency and rotordynamic stability of high-pressure compressors and steam turbines can hardly be overstated. Among seal types, the interlocking labyrinth seal (ILS), having teeth on both the rotor and the stator, is able to reduce leakage up to 30% compared to other LSs with either all teeth on the rotor (TOR) or all teeth on the stator. This paper introduces a revamped facility to test gas seals for their rotordynamic performance and presents measurements of the leakage and cavity pressures in a five teeth ILS. The seal with overall length/diameter L/D = 0.3 and small tip clearance Cr/D = 0.00133 is supplied with air at T = 298 K and increasing inlet pressure Pin = 0.3–1.3 MPa, while the exit pressure/inlet pressure ratio PR = Pout/Pin is set to range from 0.3 to 0.8. The rotor speed varies from null to 10 krpm (79 m/s max. surface speed). During the tests, instrumentation records the seal mass flow (m˙) and static pressure in each cavity. In parallel, a bulk-flow model (BFM) and a computational fluid dynamics (CFD) analysis predict the flow field and deliver the same performance characteristics, namely leakage and cavity pressures. Both measurements and predictions agree closely (within 5%) and demonstrate that the seal mass flow rate is independent of rotor speed. A modified flow factor Φ¯=m˙T/(PinD1PR2) characterizes best the seal mass flow with a unique magnitude for all pressure conditions, Pin and PR.

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References

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Figures

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Fig. 1

Schematic view of an ILS (drawing not to scale)

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Fig. 2

Cross-sectional view [8] and aerial photograph of test rig for gas seals

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Fig. 3

(a) Cross-sectional view of housing and seal section; (b) center ring with swirl injection holes; (c) photograph of two seal halves and ring showcasing location of sensors for cavity pressures

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Fig. 4

Diagram (not to scale) of air flow from a source through test housing/seal section to exit/discharge

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Fig. 5

Schematic side view of test seal and pressure sensors location

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Fig. 6

Isometric view of housing holding test seals and a central insert with a swirl vane. Graph depicts connection of ends of differential pressure transducers into a muffler plenum.

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Fig. 7

2D CFD model, mesh and applied boundary conditions for test ILS

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Fig. 8

Measured ILS mass flow rate versus pressure difference (Pin − Pout) and operation at three pressure ratios (PR = 0.3, 0.5, 0.8) and three rotor speeds (Ω = 0, 7.5, 10 krpm)

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Fig. 9

Measured ILS mass flow rate versus CFD and BFM predictions. Inlet pressure Pin increases and pressure ratio PR = 0.3, 0.5, 0.8. Rotor speed Ω = 7.5 krpm (½DΩ = 59 m/s).

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Fig. 10

Measured cavity pressure (Pcav/Pin) versus cavity # for pressure ratios PR = 0.3, 0.5, and 0.8. Inlet pressure Pin ranges from 292 kPa to 905 kPa. Rotor speed Ω = 0 and 7.5 krpm (½D Ω = 0, 59 m/s).

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Fig. 11

Measured cavity pressure (Pcav/Pin) versus cavity # for operation at rotor speeds = 0, 5 krpm, and 7.5 krpm. Inlet pressure Pin ranges from 300 kPa to 600 kPa and pressure ratio PR = 0.5.

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Fig. 12

CFD predicted flow field in last cavity of ILS and Mach number. Seal operates at Pin = 363 kPa, PR = 0.3, 0.5, 0.8, and rotor speed Ω = 7.5 krpm (½DΩ = 59 m/s).

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Fig. 13

Cavity pressures (Pcav_i/Pin): (a) CFD and BFM predicted and (b) measured. ILS operates at Pin = 292–1150 kPa, PR = 0.3–0.8, and rotor speed Ω = 0–10 krpm (RΩ = 0–79 m/s).

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Fig. 14

Experimentally derived and predicted flow factor ϕ versus pressure difference and pressure ratio PR = 0.3, 0.5, 0.8. Rotor speed Ω = 0, 3, 7.5, and 10 krpm (bars denote uncertainty).

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Fig. 15

Experimentally derived and predicted flow factor ϕ versus pressure ratio and a number of inlet pressure conditions. Rotor speed = 7.5 krpm.

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Fig. 16

Schematic view of (a) test ILS and (b) an equivalent seal (single tooth) with an effective clearance

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Fig. 17

Modified flow factor Φ¯ versus inlet pressure and three pressure ratios PR = 0.3, 0.5, 0.8. Rotor speed Ω = 0, 3, 7.5, and 10 krpm. Box denotes one standard deviation.

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