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Research Papers

Numerical Investigations on Rotordynamic Characteristic of Hole-Pattern Seals With Two Different Hole-Diameters

[+] Author and Article Information
Xin Yan

Institute of Turbomachinery,
Xi'an Jiaotong University,
Xi'an 710049, China
e-mail: xinyan@mail.xjtu.edu.cn

Kun He

MOE Key Laboratory of Thermo-Fluid Science and Engineering,
Xi'an Jiaotong University,
Xi'an 710049, China
e-mail: hekun@mail.xjtu.edu.cn

Jun Li

Institute of Turbomachinery,
Xi'an Jiaotong University,
Xi'an 710049, China
Collaborative Innovation Center of Advanced Aero-Engine,
Beijing 100191, China
e-mail: junli@mail.xjtu.edu.cn

Zhenping Feng

Institute of Turbomachinery,
Xi'an Jiaotong University,
Xi'an 710049, China
e-mail: zpfeng@mail.xjtu.edu.cn

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received May 1, 2014; final manuscript received November 22, 2014; published online January 21, 2015. Assoc. Editor: Rakesh Srivastava.

J. Turbomach 137(7), 071011 (Jul 01, 2015) (18 pages) Paper No: TURBO-14-1058; doi: 10.1115/1.4029239 History: Received May 01, 2014; Revised November 22, 2014; Online January 21, 2015

The rotordynamic characteristic of the hole-pattern seals with two different hole-diameters was investigated using the unsteady Reynolds-averaged Navier–Stokes (URANS) equations solutions and bulk flow methods. The mesh deformation method combined with elliptical orbit model was adopted to numerically solve the transient flow fields. By integrating the transient reaction forces on the rotor surface, the rotordynamic coefficients of the hole-pattern seals at a set of excitation frequencies were obtained with the reaction-force/motion model. The effects of mesh density, constant temperature assumption, and turbulence model on the numerical accuracy were analyzed for both large hole-diameter hole-pattern (LDHP) and small hole-diameter hole-pattern (SDHP) seals. The comparisons between the two bulk flow methods (i.e., the isothermal bulk flow method (ISOTSEAL) and the ideal gas bulk flow method with energy equation (ideal gas bulk flow model)) and transient computational fluid dynamics (CFD) method were performed. It shows that, compared to the experimental data, the isothermal URANS (constant temperature assumption) and total energy URANS (consider the temperature varying) solutions almost have the same accuracy with respect to the rotordynamic coefficients predictions. However, for the direct damping coefficient predictions, the total energy URANS method has a slight advantage over the isothermal URANS for both SDHP and LDHP cases. For the LDHP seal, the predicted rotordynamic coefficients are not sensitive to the selected turbulence models, but as the hole-diameter becomes smaller, the effect of turbulence model on the numerical accuracy becomes pronounced. Among the studied numerical methods, the isothermal URANS solutions with standard k–ε turbulence model have a good performance taking both numerical accuracy and computational time into consideration. For the SDHP seal, the present ideal gas bulk flow method and ISOTSEAL can provide the reasonable predictions of the rotordynamic coefficients. However, for the LDHP seal, both of them show a low accuracy in predicting the rotordynamic coefficients.

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Figures

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Fig. 1

Locations of hole-pattern seal in a centrifugal compressor [11]

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Fig. 2

Hole-pattern seal stator [11]

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Fig. 3

Section view of the test rig [10]

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Fig. 4

Dimensions of the hole-pattern (a) SDHP [8] and (b) LDHP (unit: mm) [10]

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Fig. 5

Computational models and meshes for the hole-pattern seals (fluid domain). (a) SDHP seal. (b) LDHP seal.

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Fig. 6

Fluid forces on the seal rotor, SDHP. (a) 100 Hz, isothermal URANS, k-ε. (b) 100 Hz, total energy URANS, SST.

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Fig. 7

Fluid forces on the seal rotor, LDHP. (a) 100 Hz, isothermal URANS, k-ε. (b) 100 Hz, total energy URANS, SST.

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Fig. 8

Grid sensitivity analysis for LDHP seal. (a) Cross-coupled damping Cxy. (b) Direct damping Cxx. (c) Cross-coupled stiffness Kxy. (d) Direct stiffness Kxx. (e) Effective damping Ceff. (f) Effective stiffness Keff.

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Fig. 9

Grid sensitivity analysis for SDHP seal. (a) Cross-coupled damping Cxy. (b) Direct damping Cxx. (c) Cross-coupled stiffness Kxy. (d) Direct stiffness Kxx. (e) Effective damping Ceff. (f) Effective stiffness Keff.

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Fig. 10

Rotordynamic coefficients predictions for LDHP seal. (a) Cross-coupled damping Cxy. (b) Direct damping Cxx. (c) Cross-coupled stiffness Kxy. (d) Direct stiffness Kxx.

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Fig. 11

Comparisons of the pressure and shear stress between the URANS and bulk flow method (f = 320 Hz). (a) Averaged static pressure along axial direction. (b) Averaged circumferential shear stress on rotor. (c) Averaged axial shear stress on rotor. (d) Averaged circumferential shear stress on stator. (e) Averaged axial shear stress on stator.

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Fig. 12

Rotordynamic coefficients predictions for SDHP seal. (a) Cross-coupled damping Cxy. (b) Direct damping Cxx. (c) Cross-coupled stiffness Kxy. (d) Direct stiffness Kxx.

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Fig. 13

Rotordynamic coefficients predictions for LDHP seal with different turbulence models. (a) Cross-coupled damping Cxy. (b) Direct damping Cxx. (c) Cross-coupled stiffness Kxy. (d) Direct stiffness Kxx. (e) Effective damping Ceff. (f) Effective stiffness Keff.

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Fig. 14

Rotordynamic coefficients predictions for SDHP seal with different turbulence models. (a) Cross-coupled damping Cxy. (b) Direct damping Cxx. (c) Cross-coupled stiffness Kxy. (d) Direct stiffness Kxx. (e) Effective damping Ceff. (f) Effective stiffness Keff.

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Fig. 15

Transient static pressure contours on the rotor surface for LDHP seal (f = 320 Hz)

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Fig. 16

Transient static pressure contours on the stator surface for LDHP seal (f = 320 Hz)

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Fig. 17

Transient static pressure contours on the rotor surface for SDHP seal (f = 200 Hz)

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Fig. 18

Transient static pressure contours on the stator surface for SDHP seal (f = 200 Hz)

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Fig. 19

Transient static pressure distributions on the rotor surface for LDHP seal (f = 320 Hz)

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Fig. 20

Transient static pressure distributions on the rotor surface for SDHP seal (f = 200 Hz)

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