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Research Papers: Gas Turbines: Heat Transfer

Brush Seals Used in Steam Environments—Chronological Wear Development and the Impact of Different Seal Designs

[+] Author and Article Information
Markus Raben

Institute of Jet Propulsion and Turbomachinery,
TU Braunschweig,
Hermann-Blenk-Str. 37,
Braunschweig 38108, Germany
e-mail: m.raben@ifas.tu-bs.de

Jens Friedrichs

Institute of Jet Propulsion and Turbomachinery,
TU Braunschweig,
Hermann-Blenk-Str. 37,
Braunschweig 38108, Germany
e-mail: j.friedrichs@ifas.tu-bs.de

Thomas Helmis

Siemens AG,
Power and Gas Division,
Rheinstr. 100,
Mülheim an der Ruhr 45478, Germany
e-mail: thomas.helmis@siemens.com

Johan Flegler

Siemens AG,
Power and Gas Division,
Rheinstr. 100,
Mülheim an der Ruhr 45478, Germany
e-mail: johan.flegler@siemens.com

1Corresponding author.

Contributed by the Heat Transfer Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received July 15, 2015; final manuscript received August 30, 2015; published online October 27, 2015. Editor: David Wisler.

J. Eng. Gas Turbines Power 138(5), 051901 (Oct 27, 2015) (10 pages) Paper No: GTP-15-1318; doi: 10.1115/1.4031531 History: Received July 15, 2015; Revised August 30, 2015

During the last decades, turbo machine efficiency was considerably increased by using more efficient seals. Brush seals, as a compliant contacting filament seal, have become an attractive alternative to conventional labyrinth seals in the field of aircraft engines as well as in stationary gas and steam turbines. The aim of today's research related to brush seals is to understand the characteristics and their connections, in order to be able to make performance predictions, and to ensure the reliability over a defined operating period. The wear behavior is essentially influenced by frictional contacts at the seal-to-rotor interface during operation. For realistic investigations with representative circumferential velocities, the TU Braunschweig, Germany, operates a specially developed steam test rig which enables endurance investigations under varying operating steam conditions up to 50 bar and 450 °C. Wear measurements and the determination of seal performance characteristics, such as blow down and bristle stiffness, are enabled by an additional test facility, using pressurized cold air up to 8 bar as a working fluid. This work presents the chronological wear development on both rotor and seal sides in a steam test lasting 25 days or 11 days, respectively. Interruptions after stationary and transient intervals were made in order to investigate the degree of wear. Two different seal arrangements, a single tandem seal, and a two-stage single seal arrangement, using different seal elements were considered. Besides a continuous wear development, the results clearly show that the abrasive wear of the brush seal and rotor is mainly caused by transient test operations, particularly by enforced contacts during shaft excursions. Despite the increasing wear to the brushes, all seals have shown a functioning radial-adaptive behavior over the whole test duration with a sustained seal performance. Thereby, it could be shown that the two-stage arrangement displays a load shift during transients, leading to a balanced loading and unloading status for the two single brush seals. From load sharing, and in comparison with the wear data of the tandem seal arrangement, it can be derived that the two-stage seal is less prone to wear. However, the tandem seal arrangement, bearing the higher pressure difference within one configuration, shows a superior sealing performance under constant load, i.e., under stationary conditions.

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References

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Figures

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Fig. 1

Axial inclination (left) and lay angle (right) [6]

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Fig. 2

Brush seal behavior for different axial inclinations [6]

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Fig. 4

Brush seal configurations

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Fig. 5

Single pressure differences (BST15a)

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Fig. 6

Discharge coefficients (BST15a)

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Fig. 7

Blow down (BST15a)

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Fig. 8

Bristle pack stiffness (BST15a)

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Fig. 9

Bristle pack width (BST15a)

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Fig. 10

Oscillating bristle rows, seal DS1 (Δp = 5 bar)

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Fig. 11

Inlet pressure variation—single pressure differences (BST16a)

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Fig. 12

Inlet pressure variation—discharge coefficients (BST16a)

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Fig. 13

Eccentricity variation—single pressure differences (BST16a)

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Fig. 14

Eccentricity variation—discharge coefficients (BST16a)

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Fig. 15

Cold clearances—chronological development

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Fig. 16

Cold clearances—circumferential profile, seal DS1

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Fig. 17

Cold clearances—circumferential profile, seal DS2

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Fig. 18

Shaft wear—maximum profile depth

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