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Research Papers: Gas Turbines: Structures and Dynamics

Computational Fluid Dynamics Investigation of Labyrinth Seal Leakage Performance Depending on Mushroom-Shaped Tooth Wear

[+] Author and Article Information
Yahya Dogu

Department of Mechanical Engineering,
Kirikkale University,
Yahsihan, Kirikkale 71450, Turkey
e-mail: yahya.dogu@hotmail.com

Mustafa C. Sertçakan

Department of Mechanical Engineering,
Kirikkale University,
Yahsihan, Kirikkale 71450, Turkey
e-mail: mcem_sertcakan@hotmail.com

Ahmet S. Bahar

Department of Mechanical Engineering,
Kirikkale University,
Yahsihan, Kirikkale 71450, Turkey
e-mail: ahmetserhatbahar@gmail.com

Altuğ Pişkin

TUSAS Engine Industries, Inc. (TEI),
Eskisehir 26003, Turkey
e-mail: altug.piskin@tei.com.tr

Ercan Arıcan

TUSAS Engine Industries, Inc. (TEI),
Eskisehir 26003, Turkey
e-mail: ercan.arican@tei.com.tr

Mustafa Kocagül

TUSAS Engine Industries, Inc. (TEI),
Eskisehir 26003, Turkey
e-mail: mustafa.kocagul@tei.com.tr

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 15, 2015; final manuscript received August 12, 2015; published online September 29, 2015. Editor: David Wisler.

J. Eng. Gas Turbines Power 138(3), 032503 (Sep 29, 2015) (10 pages) Paper No: GTP-15-1319; doi: 10.1115/1.4031369 History: Received July 15, 2015; Revised August 12, 2015

Conventional labyrinth seal applications in turbomachinery encounter a permanent teeth tip damage and wear during transitional operations. This is the dominant issue that causes unpredictable seal leakage performance degradation. Since the gap between the rotor and the stator changes depending on engine transitional operations, labyrinth teeth located on the rotor/stator wear against the stator/rotor. This wear is observed mostly in the form of the labyrinth teeth becoming a mushroom shape. It is known that, as a result of this tooth tip wear, leakage performance permanently decreases, which negatively affects the engine's overall efficiency. However, very limited information about leakage performance degradation caused by mushroom wear is available in open literature. This paper presents a study that numerically quantifies leakage values for various radii of mushroom-shaped labyrinth teeth by changing tooth-surface clearance, pressure ratio, number of teeth, and rotor speed. Analyzed parameters and their ranges are mushroom radius (R = 0–0.508 mm), clearance (cr = 0.254–2.032 mm), pressure ratio (Rp = 1.5–3.5), number of teeth (nt = 1–12), and rotor speed (n = 0–80 krpm). Computational fluid dynamics (CFD) analyses were carried out by employing compressible turbulent flow in 2D axisymmetrical coordinate system. CFD leakage results were also compared with well-known labyrinth seal semi-empirical correlations. Given a constant clearance, leakage increases with the size of the mushroom radius that forms on the tooth. This behavior is caused by less flow separation and flow disturbance, and the vena contracta effect for flow over the smoothly shaped mushroom tooth tip compared to the sharp-edged tooth tip. This leakage increase is higher when the tooth tip wear is considered as an addition to the unworn physical clearance, since the clearance dominates the leakage. The leakage affected by the number of teeth was also quantified with respect to the mushroom radius. The rotational effect was also studied as a secondary parameter.

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Figures

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Fig. 9

Stream function for unworn and worn tooth

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Fig. 10

Static pressure change at midline of clearance

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Fig. 11

Mach number change at midline of clearance

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Fig. 8

Velocity vectors for unworn and worn tooth

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Fig. 7

Velocity magnitude contours for unworn and worn tooth

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Fig. 6

Static pressure contours for unworn and worn tooth

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Fig. 5

Representative mesh generation

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Fig. 4

Geometric dimensions of mushroomed tooth

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Fig. 3

Representative labyrinth seal geometry and boundary conditions

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Fig. 2

Approximate geometry of the mushroom-shaped teeth used for modeling (all dimensions are in mm)

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Fig. 1

Photographs of tooth tip wear: (a) Ref. [18]; (b) Ref. [19]; and (c) Ref. [20]

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Fig. 18

Leakage change with respect to number of teeth

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Fig. 19

Amount and percentage of leakage reduction for increment of number of teeth

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Fig. 20

Leakage with respect rotor speed

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Fig. 12

Pressure load over first and last (fourth) tooth with respect pressure ratio and Mach number for mushroom radius of R = 0.254 mm

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Fig. 13

Leakage results from CFD and other correlations

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Fig. 14

Leakage comparison: (a) stepped labyrinth seal [21] and (b) straight-through labyrinth seal

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Fig. 15

Leakage with respect to mushroom radius for constant clearance

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Fig. 16

Leakage with respect to mushroom radius for variable clearance

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Fig. 17

Leakage with respect to pressure ratio and mushroom radius or clearance

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