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Research Papers: Gas Turbines: Structures and Dynamics

Leakage and Rotordynamic Coefficients of Brush Seals With Zero Cold Clearance Used in an Arrangement With Labyrinth Fins

[+] Author and Article Information
Manuel Gaszner

Research Assistant break/>e-mail: gaszner@es.mw.tum.de

Alexander O. Pugachev

Research Associate
e-mail: pugachev@tum.de

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

Christos Georgakis

Manager, CT Blades,
ALSTOM,
Rugby CV21 2NH, UK
e-mail: christos.georgakis@power.alstom.com

Paul Cooper

Steam Turbines Chief Engineers Office,
ALSTOM,
Rugby CV21 2NH, UK
e-mail: paul.cooper@power.alstom.com

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 June 13, 2013; final manuscript received August 1, 2013; published online September 23, 2013. Editor: David Wisler.

J. Eng. Gas Turbines Power 135(12), 122506 (Sep 23, 2013) (11 pages) Paper No: GTP-13-1167; doi: 10.1115/1.4025236 History: Received June 13, 2013; Revised August 01, 2013

A brush-labyrinth sealing configuration consisting of two labyrinth fins upstream and one brush seal downstream is studied experimentally and theoretically. Two slightly different brush seal designs with zero cold radial clearance are considered. The sealing configurations are tested on the no-whirl and dynamic test rigs to obtain leakage performance and rotordynamic stiffness and damping coefficients. The no-whirl tests allow identification of the local rotordynamic direct and cross-coupled stiffness coefficients for a wide range of operating conditions, while the dynamic test rig is used to obtain both global stiffness and damping coefficients but for a narrower operating range limited by the capabilities of a magnetic actuator. Modeling of the brush-labyrinth seals is performed using computational fluid dynamics. The experimental global rotordynamic coefficients consist of an aerodynamic component due to the gas flow and a mechanical component due to the contact between the bristle tips and rotor surface. The computational fluid dynamics (CFD)–based calculations of rotordynamic coefficients provide, however, only the aerodynamic component. A simple mechanical model is used to estimate the theoretical value of the mechanical stiffness of the bristle pack during the contact. The results obtained for the sealing configurations with zero cold radial clearance brush seals are compared with available data on three-tooth-on-stator labyrinth seals and a brush seal with positive cold radial clearance. Results show that the sealing arrangement with a line-on-line welded brush seal has the best performance overall with the lowest leakage and cross-coupled stiffness. The predictions are generally in agreement with the measurements for leakage and stiffness coefficients. The seal-damping capability is noticeably underpredicted.

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References

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Figures

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Fig. 1

Air supply and swirl generator system

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Fig. 2

The no-whirl test rig (left) and eccentric rotor operation (right)

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Fig. 3

The dynamic test rig (top) and magnetic actuator operation (bottom)

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Fig. 4

Schemes of the sealing arrangements

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Fig. 5

Experimental effective clearance for various sealing configurations versus pressure ratio

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Fig. 6

Experimental local stiffness coefficients for medium preswirl

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Fig. 7

Preswirl influence on the experimental local stiffness coefficients (SSB-1 and SSB-2 seals)

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Fig. 8

Effect of rotational speed on the experimental local stiffness coefficients

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Fig. 9

Experimental global rotordynamic coefficients for medium preswirl

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Fig. 10

Computational model of the SSB-1 seal

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Fig. 11

Single bristle as cantilever beam [14]

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Fig. 12

Experimental and predicted leakage for the SSB-1 and SSB-2 seals

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Fig. 13

Experimental and predicted local stiffness coefficients for the SSB-1 and SSB-2 seals

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Fig. 14

Experimental and predicted global rotordynamic coefficients for the SSB-1 and SSB-2 seals

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