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Gas Turbines: Structures and Dynamics

Prediction of Rotordynamic Coefficients for Short Labyrinth Gas Seals Using Computational Fluid Dynamics

[+] Author and Article Information
Alexander O. Pugachev1

Institute of Energy Systems,  Technische Universität München, Boltzmannstrasse 15, 85748 Garching, Germanypugachev@tum.de

Ulrich Kleinhans, Manuel Gaszner

Institute of Energy Systems,  Technische Universität München, Boltzmannstrasse 15, 85748 Garching, Germany

1

Corresponding author.

J. Eng. Gas Turbines Power 134(6), 062501 (Apr 12, 2012) (10 pages) doi:10.1115/1.4005971 History: Received July 18, 2011; Revised November 10, 2011; Published April 09, 2012; Online April 12, 2012

The analysis is presented for the computational fluid dynamics (CFD)-based modeling of short labyrinth gas seals. Seal leakage performance can be reliably predicted with CFD for a wide operating range and various sealing configurations. Prediction of seal influence on the rotordynamic stability, however, is a challenging task requiring relatively high computer processing power. A full 3D eccentric CFD model of a short staggered three-tooth-on-stator labyrinth seal is built in ANSYS CFX. An extensive grid independence study is carried out showing influence of the grid refinement on the stiffness coefficients. Three methods for the prediction of stiffness and damping coefficients as well as the effect of turbulence modeling, boundary conditions, and solver parameters are presented. The rest of the paper shows the results of a parameter variation (inlet pressure, preswirl, and shaft rotational speed) for two labyrinth seals with a tooth radial clearance of 0.5 mm and 0.27 mm, respectively. The latter was compared with experimental data in Pugachev and Deckner, 2010, “Analysis of the Experimental and CFD-Based Theoretical Methods for Studying Rotordynamic Characteristics of Labyrinth Gas Seals,” Proceedings of ASME Turbo Expo 2010, Paper No. GT2010-22058.

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Copyright © 2012 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Geometry of the three-tooth-on-stator staggered labyrinth seal (SSS seal)

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Figure 2

Computational model of the short labyrinth gas seal

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Figure 3

Dynamic model of the seal

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Figure 4

Predicted pressure distribution in two sealing cavities; dashed lines show the position of planes for the determination of local coefficients

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Figure 5

Angle of peak pressure as a function of axial distance on rotor and stator

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Figure 6

Results of the mesh density study for the stiffness coefficients

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Figure 7

Tooth region in the final mesh

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Figure 8

Experimental and theoretical stiffness coefficients for the SSS labyrinth seal with 0.27 mm tooth radial clearance from Ref. [1] (direct stiffness versus leakage, cross-coupled stiffness versus inflow swirl force)

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Figure 9

Predicted leakage for different tooth radial clearances

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Figure 10

Global stiffness (a) and damping (b) coefficients for different tooth radial clearances

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Figure 11

Global stiffness (a) and damping (b) coefficients as functions of inlet swirl and inlet pressure

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