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Research Papers: Flows in Complex Systems

Elliptical Shape Hole-Pattern Seals Performance Evaluation Using Design of Experiments Technique1

[+] Author and Article Information
Hanxiang Jin

Laboratory for Turbomachinery
and Components,
Department of Biomedical
Engineering and Mechanics,
Virginia Tech,
Norris Hall, Room 324, 495 Old Turner Street,
Blacksburg, VA 24061
e-mail: hj3dy@vt.edu

Alexandrina Untaroiu

Laboratory for Turbomachinery
and Components,
Department of Biomedical
Engineering and Mechanics,
Virginia Tech,
Norris Hall, Room 324, 495 Old Turner Street, Blacksburg, VA 24061
e-mail: alexu@vt.edu

Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received September 26, 2016; final manuscript received January 24, 2018; published online March 16, 2018. Assoc. Editor: Wayne Strasser.

J. Fluids Eng 140(7), 071101 (Mar 16, 2018) (16 pages) Paper No: FE-16-1631; doi: 10.1115/1.4039249 History: Received September 26, 2016; Revised January 24, 2018

Hole-pattern annular gas seals have two distinct flow regions: an annular jet-flow region between the rotor and stator, and cylindrical indentions in the stator that serve as cavities where flow recirculation occurs. As the working fluid enters the cavities and recirculates, its kinetic energy is reduced, resulting in a reduction of leakage flow rate through the seal. The geometry of the cylindrical cavities has a significant effect on the overall performance of the seal. In this study, the effects of elliptical shape hole pattern geometry on the leakage and dynamic response performance of an industry-relevant hole-pattern seal design are investigated using a combination of computational fluid dynamics (CFD), hybrid bulk flow-CFD analysis, and design of experiments (DOEs) technique. The design space was defined by varying the values of five geometrical characteristics: the major and minor radius of hole, the angle between the major axis and the axis of the seal, the spacing between holes along the seal axis, and hole spacing in the circumferential direction. This detailed analysis allowed for a greater understanding of the interaction effects from varying all of these design parameters together as opposed to studying them one variable at a time. Response maps generated from the calculated results demonstrate the effects of each design parameter on seal leakage as well as the co-dependence between the design parameters. The data from this analysis were also used to generate linear regression models that demonstrate how these parameters affect the leakage rate and the dynamic coefficients, including the effective damping.

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Figures

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Fig. 1

Seal geometry: (a) fluid domain of baseline model and (b) cross section view of hole-pattern seal

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Fig. 2

Illustration of (a) geometry variables and constrains for the design space and (b) example of elliptical shape surface patterning obtained through parametrization

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Fig. 3

(a) Mesh for baseline model and (b) detail view

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Fig. 4

Velocity plot for baseline model: (a) vector plot and (b) contour plot

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Fig. 5

Leakage rate (kg/s) versus two design variables: (a) rab and a and (b) nc and rab

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Fig. 6

Response surfaces for the direct stiffness (N/m) versus design variables: (a) rab and a and (b) na and nc

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Fig. 7

Response surfaces of cross-coupled stiffness (N/m) versus design variables: (a) θ and a, (b) θ and rab, and (c) na and nc

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Fig. 8

Response surfaces of direct damping (N s/m) versus design variables: (a) rab and a and (b) na and nc

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Fig. 9

Response surfaces of effective damping versus (a) θ and a, (b) θ and rab, and (c) nc and θ

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Fig. 10

Comparison of predicted regression model with actual values from all design points for: (a) leakage rate, (b) direct stiffness, (c) cross-coupled stiffness, (d) direct damping, and (e) effective damping coefficient

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Fig. 11

Seal geometry with high performance leakage rate characteristics: (a) pressure contour, (b) velocity plot, and (c) velocity contour

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Fig. 12

Seal geometry with a low performance leakage rate characteristics: (a) pressure contour, (b) velocity plot, and (c) velocity contour

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Fig. 13

Pressure contours—comparison between the high and low performance leakage rate seal models: (a) side by side comparison and (b) difference plot for pressure for the two seal models

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Fig. 14

Velocity contours—comparison between the high and low performance leakage rate seal models: (a) side by side comparison and (b) difference plot

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Fig. 15

High performance seal geometry—corresponding to a higher effective damping coefficient compared to baseline design which indicates a better stability potential: (a) pressure contour, (b) velocity plot, and (c) velocity contour

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Fig. 16

Low performance seal geometry—corresponding to a lower effective damping coefficient compared to baseline design, which indicates a poorer stability potential: (a) pressure contour, (b) velocity plot, and (c) velocity contour

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Fig. 17

Pressure contours—comparison between the high and low performance seal geometry for effective damping coefficient: (a) side by side comparison and (b) difference plot

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Fig. 18

Velocity contour—comparison between the high and low performance seal geometry for effective damping coefficient: (a) side by side comparison and (b) difference plot

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