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Research Papers: Gas Turbines: Structures and Dynamics

Leakage Degradation of Straight Labyrinth Seal Due to Wear of Round Tooth Tip and Acute Trapezoidal Rub-Groove

[+] Author and Article Information
Yahya Dogu

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

Mustafa C. Sertçakan

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

Koray Gezer

Mechanical Engineering Department,
Kirikkale University,
Yahsihan,
Kirikkale 71450, Turkey
e-mail: koraygezer90@gmail.com

Mustafa Kocagül

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

Ercan Arıcan

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

Murat S. Ozmusul

Pro Solutions USA LLC,
453 Kinns Road,
Clifton Park, NY 12065
e-mail: ozmusul@prousa.us

Contributed by the Structures and Dynamics Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received August 9, 2016; final manuscript received December 15, 2016; published online March 7, 2017. Editor: David Wisler.

J. Eng. Gas Turbines Power 139(7), 072506 (Mar 07, 2017) (12 pages) Paper No: GTP-16-1399; doi: 10.1115/1.4035657 History: Received August 09, 2016; Revised December 15, 2016

In this paper, labyrinth seal leakage is numerically quantified for an acute trapezoidal rub-groove accompanied with a rounded tooth, as a function of rub-groove sizes and tooth-groove axial positions. Analyses parameters include clearance, pressure ratio, number of teeth, and rotor speed. Labyrinth seals wear during engine transients. Radial incursion and axial movement of the rotor–stator pair cause the labyrinth teeth to rub against the unworn stator surface. The labyrinth teeth and/or stator wear depending on their material hardness. Wear damage in the form of material loss or deformation permanently increases seal clearance, and thus, leakage. This leakage is known to be dependent on the shape and geometry of the worn tooth and the stator rub groove. There are two types of reported tooth tip wear. These can be approximated as a mushroom shape and a round shape. The stator rub-groove shapes can be approximately simulated in five forms: rectangle, trapezoid (isosceles and acute), triangle, and ellipse. In this paper, the acute trapezoidal rub-groove shape is specifically chosen, since it is the most similar to the most commonly observed rub-groove form. The tooth tip is considered to be rounded, because the tooth tip wears smoothly and a round shape forms during rub-groove formation. To compare the unworn tooth, the flat stator is also analyzed as a reference case. All analyzed parameters for geometric dimensions (groove width, depth, wall angle, and tooth-groove axial position) and operating conditions (flow direction, clearance, pressure ratio, number of teeth, and rotor speed) are analyzed in their practical ranges. Computational fluid dynamics (CFD) analyses are carried out by employing a compressible turbulent flow solver in a 2D axisymmetrical coordinate system. CFD analyses show that the rounded tooth leaks more than an unworn sharp-edged tooth, due to the formation of a smooth and streamlined flow around the rounded geometry. This smooth flow yields less flow separation, flow disturbance, and less of vena contracta effect. The geometric dimensions of the acute trapezoidal rub-groove (width, depth, wall angle) significantly affect leakage. The effects of clearance, pressure ratio, number of teeth, and rotor speed on the leakage are also quantified. Analyses results are separately evaluated for each parameter.

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Figures

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Fig. 1

Photographs for shapes of tooth tip wear and rub-groove: (a) [8], (b) [2], (c) [3], (d) [4], (e) [5], (f) [6], (g) [7], (h) [9], (i) [8], (j) [10], (k) [4], and (l) [11]

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Fig. 2

Possible wear shapes for tooth and rub-groove

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Fig. 3

Geometry of round tooth and rub-groove

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Fig. 4

Representative labyrinth seal geometry and boundary conditions

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Fig. 5

Representative mesh generation

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Fig. 6

Test and CFD model comparisons (a) straight labyrinth seal without rub-groove and (b) stepped labyrinth seal with rub-groove

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Fig. 7

Flow pattern plots for unworn seal and worn tooth with groove: (a) nondimensional pressure contours, (b) Mach number contours, (c) velocity vectors, and (d) velocity vectors around first tooth

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Fig. 8

Nondimensional pressure change at midline of clearance

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Fig. 9

Leakage and discharge coefficient versus groove width

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Fig. 10

Leakage and discharge coefficient versus groove depth

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Fig. 11

Discharge coefficient versus tooth-groove axial position

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Fig. 12

Leakage and discharge coefficient versus groove wall angle at downstream side

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Fig. 13

Leakage and discharge coefficient for straight and reversed flow directions

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Fig. 14

Leakage and discharge coefficient versus tooth clearance

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Fig. 15

Leakage and discharge coefficient versus pressure ratio

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Fig. 16

(a) Leakage and discharge coefficient versus number of teeth and (b) percentage of leakage reduction for increment of number of teeth

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Fig. 17

Leakage and discharge coefficient versus rotor speed

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Fig. 18

Velocity vectors and Mach number around first tooth for n = 0 and 40 krpm

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Fig. 19

Nondimensional axial velocity at first tooth clearance region showing vena contracta effect for n = 0 and 40 krpm

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