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Research Papers: Hydrodynamic Lubrication

Comparisons of Rotordynamic Characteristics Predictions for Annular Gas Seals Using the Transient Computational Fluid Dynamic Method Based on Different Single-Frequency and Multifrequency Rotor Whirling Models

[+] Author and Article Information
Zhigang Li

Institute of Turbomachinery
School of Energy & Power Engineering,
Xi'an Jiaotong University,
Xi'an 710049, China

Jun Li

Institute of Turbomachinery
School of Energy & Power Engineering,
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
School of Energy & Power Engineering,
Xi'an Jiaotong University,
Xi'an 710049, China

1Corresponding author.

Contributed by the Tribology Division of ASME for publication in the JOURNAL OF TRIBOLOGY. Manuscript received December 17, 2014; final manuscript received June 7, 2015; published online July 23, 2015. Assoc. Editor: Mihai Arghir.

J. Tribol 138(1), 011701 (Jul 23, 2015) (18 pages) Paper No: TRIB-14-1308; doi: 10.1115/1.4030807 History: Received December 17, 2014

The three-dimensional (3D) transient computational fluid dynamic (CFD) method was proposed to predict rotordynamic coefficients for annular gas seals. This transient CFD method uses unsteady Reynolds-Averaged Navier–Stokes (RANS) solution technique and mesh deformation theory, which requires a rotor whirling model as the rotor excitation signal to solve the transient leakage flow field in seal and obtain the transient fluid response forces on the rotor surface. A fully partitioned pocket damper seal (FPDS) was taken as the test object to validate the present numerical method. Comparisons were made between experimental data and rotordynamic coefficient predictions using the three variations of the single-frequency and multiple-frequency rotor whirling models: (1) one-dimensional whirling model, (2) circular orbit whirling model, and (3) elliptical orbit whirling model. The numerical results show that the rotordynamic coefficients predicted by the present CFD method and six different rotor whirling models all agree well with the experiment data, and nearly coincide for all rotor whirling models. The proposed transient CFD method can be used to perform a reasonably accurate prediction of the frequency-dependent rotordynamic coefficients for annular gas seals based on any one of the present six rotor whirling models, as long as ensuring the combination of these whirling model parameters captures the small perturbation theory. The rotor whirling parameters such as whirling orbit, amplitude, and frequency number are important in predicting rotor whirling motion and fluid response forces, but have almost no effect on the computed rotordynamic coefficients. The benefit of the multiple-frequency rotor whirling models is the ability to calculate accurate rotordynamic coefficients of annular gas seals in a wide frequency range with a simulation time on the order of one-tenth the cost of the single-frequency whirling models.

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Figures

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Fig. 1

Schematic of one-control-volume and two control-volume bulk-flow models

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Fig. 2

Frame transfer from stationary to rotating (steady-state CFD-based method)

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Fig. 3

Three types of rotor vibration analysis models with two degrees-of-freedom (2DOF): (a) straight line orbit, (b) circle orbit, and (c) elliptical orbit

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Fig. 4

1D rotor whirling model

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Fig. 5

Circle orbit rotor whirling model

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Fig. 6

Elliptical orbit rotor whirling model

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Fig. 7

Geometry of the experimental FPDS [41]

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Fig. 8

Computational model and mesh of the FPDS

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Fig. 9

Multiple-frequency whirling orbits of the seal rotor: (a) 1D whirling, (b) circle orbit whirling, and (c) elliptical orbit whirling

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Fig. 10

Comparisons of predicted rotor whirling motions for three types of multiple-frequency whirling models at zero inlet preswirl, x excitation or forward whirling: (a) 1D whirling model (x excitation), (b) circle orbit whirling model (forward whirling), and (c) elliptical orbit whirling model (x excitation)

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Fig. 11

Comparisons of predicted rotor whirling motions for three types of single-frequency whirling models at zero inlet preswirl, x excitation or forward whirling: (a) 1D whirling model (x excitation), (b) circle orbit whirling model (forward whirling), and (c) elliptical orbit whirling model (x excitation)

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Fig. 12

Comparisons of predicted fluid response forces for three types of multiple-frequency whirling models at zero inlet preswirl, x excitation or forward whirling: (a) 1D whirling model (x excitation), (b) circle orbit whirling model (forward whirling), and (c) elliptical orbit whirling model (x excitation)

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Fig. 13

Comparisons of predicted fluid response forces for three types of single-frequency whirling models at zero inlet preswirl, x excitation or forward whirling: (a) 1D whirling model (x excitation), (b) circle orbit whirling model (forward whirling), and (c) elliptical orbit whirling model (x excitation)

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Fig. 14

Comparisons of predicted rotordynamic coefficients for three types of multiple-frequency whirling models at zero inlet preswirl: (a) direct stiffness, (b) direct damping, (c) cross-coupling stiffness, and (d) effective damping

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Fig. 15

Comparisons of predicted rotordynamic coefficients for three types of multiple-frequency whirling models at 60 m/s inlet preswirl: (a) direct stiffness, (b) direct damping, (c) cross-coupling stiffness, and (d) effective damping

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Fig. 16

Comparisons of static pressure contours on the cross section through the middle of annular cavity 3 and phasor diagram of the fluid response forces for three multiple-frequency whirling models at zero inlet preswirl, T=0.1s, x excitation or forward whirling: (a) one-dimensional whirling model (x excitation), (b) circle orbit whirling model (forward whirling), and (c) elliptical orbit whirling model (x excitation)

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Fig. 17

Comparisons of static pressure contours on the cross section through the middle of annular cavity 3 and phasor diagram of the fluid response forces for three single-frequency whirling models at zero inlet preswirl, T=0.1s, x excitation or forward whirling: (a) one-dimensional whirling model (x excitation), (b) circle orbit whirling model (forward whirling), and (c) elliptical orbit whirling model (x excitation)

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