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Research Papers: Gas Turbines: Structures and Dynamics

Numerical Investigations for Leakage and Windage Heating in Straight-Through Labyrinth Seals

[+] Author and Article Information
Kali Charan Nayak

Department of Mechanical Engineering,
Indian Institute of Science,
Bangalore 560012, India
e-mail: kali_nayak@yahoo.co.in

Pradip Dutta

Department of Mechanical Engineering,
Indian Institute of Science,
Bangalore 560012, India

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 August 26, 2014; final manuscript received August 8, 2015; published online September 18, 2015. Editor: David Wisler.

J. Eng. Gas Turbines Power 138(1), 012507 (Sep 18, 2015) (10 pages) Paper No: GTP-14-1515; doi: 10.1115/1.4031343 History: Received August 26, 2014; Revised August 08, 2015

The ability to quantify leakage flow and windage heating for labyrinth seals with honeycomb lands is critical in understanding gas turbine engine system performance and predicting its component life. Variety of labyrinth seal configurations (number of teeth, stepped or straight, honeycomb cell size) are in use in gas turbines, and for each configuration, there are many geometric factors that can impact a seal's leakage and windage characteristics. This paper describes the development of a numerical methodology aimed at studying the effect of honeycomb lands on leakage and windage heating. Specifically, a three-dimensional computational fluid dynamics (CFD) model is developed utilizing commercial finite volume-based software incorporating the renormalization group (RNG) k-ε turbulence model with modified Schmidt number. The modified turbulence model is benchmarked and fine-tuned based on several experiments. Using this model, a broad parametric study is conducted by varying honeycomb cell size, pressure ratio (PR), and radial clearance for a four-tooth straight-through labyrinth seal. The results show good agreement with available experimental data. They further indicate that larger honeycomb cells predict higher seal leakage and windage heating at tighter clearances compared to smaller honeycomb cells and smooth lands. However, at open seal clearances larger honeycomb cells have lower leakage compared to smaller honeycomb cells.

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Figures

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Fig. 1

Schematic of the problem of interest

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Fig. 2

(a) Computational model with boundary conditions and (b) periodic 1/2-1-1/2 HC sector grid

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Fig. 8

Windage heating comparison: CFD, analytical correlation, and experiment

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Fig. 7

Seal leakage comparison: CFD, analytical correlation, and experiment

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Fig. 6

Labyrinth seal leakage comparison for Collins experiment with 3.2 mm HCs

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Fig. 5

Labyrinth seal leakage comparison for Collins experiment with smooth lands

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Fig. 4

Seal leakage predictions at 0.5 mm clearance

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Fig. 3

Sensitivity of (a) grid resolution and (b) turbulence model on seal leakage

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Fig. 9

Velocity vectors colored by swirl (Ψ). (a) CL = 0.75mm,Smooth, (b) CL = 0.75 mm, HC = 1.588 mm, and (c) CL = 0.25mm, Smooth.

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Fig. 11

Flow field at the tooth tip for different clearances of theseal with HC = 3.2 mm, PR = 1.8. (a) CL = 0.25 mm, (b) CL = 0.5 mm, (c) CL = 1.0 mm and (d) CL = 2.0 mm.

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Fig. 12

Variation of flow parameter with clearance for different HC sizes at PR = 1.8

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Fig. 13

Flow field at the tooth tip for different clearances of theseal with HC = 0.8 mm, PR = 1.8. (a) CL = 0.25 mm, (b) CL = 0.5 mm, (c) CL = 1.0 mm, and (d) CL = 2.0 mm.

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Fig. 14

Variation of flow ratio with clearance for different HC sizes at unworn conditions

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Fig. 15

Variation of flow parameter at varied pressure ratio and clearance for (a) smooth land (b) 3.2 mm honeycomb lands

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Fig. 16

Variation of pocket swirl with clearance for different HC sizes at PR = 1.8. Pocket two swirl is taken for comparison.

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Fig. 17

Variation of windage number with clearance for different HC sizes at PR = 1.8

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Fig. 10

Variation of bypass flow for different HC sizes at unworn conditions

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Fig. 18

Velocity vectors colored by air swirl in seal region with 0.25 mm clearance for various HCs. (a) Smooth land, (b) 0.8 mm HCs, (c) 1.6 mm HCs, and (d) 3.2 mm HCs.

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Fig. 19

Velocity vectors colored by swirl in seal region with 0.5 mm clearance for various HCs. (a) 0.8 mm HCs and (b) 3.2mm HCs.

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