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Research Papers: Gas Turbines: Structures and Dynamics

Flat Plate Honeycomb Seals Friction Factor Analysis

[+] Author and Article Information
Mirko Micio

ERGON Research s.r.l.,
via Panciatichi 92,
Florence 50127, Italy
e-mail: mirko.micio@ergonresearch.it

Cosimo Bianchini

ERGON Research s.r.l.,
via Panciatichi 92,
Florence 50127, Italy
e-mail: cosimo.bianchini@ergonresearch.it

Daniele Massini

DIEF—Department of Industrial Engineering,
University of Florence,
via di S. Marta 3,
Florence 50139, Italy
e-mail: daniele.massini@unifi.it

Bruno Facchini

DIEF—Department of Industrial Engineering,
University of Florence,
via di S. Marta 3,
Florence 50139, Italy
e-mail: bruno.facchini@unifi-it

Alberto Ceccherini

GE Oil & Gas,
via F. Matteucci 2,
Florence 50127, Italy
e-mail: Alberto.Ceccherini@ge.com

Luca Innocenti

GE Oil & Gas,
via F. Matteucci 2,
Florence 50127, Italy
e-mail: Luca1.Innocenti@ge.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 September 11, 2015; final manuscript received October 15, 2015; published online December 8, 2015. Editor: David Wisler.

J. Eng. Gas Turbines Power 138(7), 072505 (Dec 08, 2015) (10 pages) Paper No: GTP-15-1446; doi: 10.1115/1.4031963 History: Received September 11, 2015; Revised October 15, 2015

Among the various types of seals used in gas turbine secondary air system to guarantee sufficient confinement of the main gas path, honeycomb seals perform well in terms of enhanced stability and reduced leakage flow. Due to the large amount of honeycomb cells typically employed in real seals, it is generally convenient to treat the sealing effect of the honeycomb pack as an increased distributed friction factor on the plain top surface. That is why, this analysis is focused on a simple configuration composed by a honeycomb facing a flat plate. In order to evaluate the sealing performance of such honeycomb packs, an experimental campaign was carried out on a stationary test rig where the effects of shaft rotation are neglected. The test rig was designed to analyze different honeycomb geometries so that a large experimental database could be created to correlate the influence of each investigated parameter. Honeycomb seals were varied in terms of hexagonal cell dimension and depth in a range that represents well actual honeycomb packs employed in industrial compressors. For each geometry, seven different clearances were tested. This work reports the findings of such experimental campaign whose results were analyzed in order to guide actual seals design and effective estimates of shaft loads. Static pressure measurements reveal that the effects of investigated geometrical parameters on friction factor correlate well with a corrected Mach number based on the cell depth. The presence of acoustic effects in the seals was further investigated by means of hot wire anemometry. Acoustic forcing due to flow cavity interaction was found to be characterized by a constant Strouhal number based on cell geometry. Numerical simulations helped in the identification of system eigenmodes and eigenfrequencies providing an explanation to the friction factor enhancement triggered at a certain flow speed. Finally, the generated dataset was tested comparing the predicted leakage flow with experimental data of actual seals (with high pressure and high rotational speed) showing a very good agreement.

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References

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Figures

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Fig. 1

Honeycomb annular seal

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Fig. 3

Postprocessing flowchart

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Fig. 4

Honeycomb seal geometry

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Fig. 5

Smooth case validation

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Fig. 6

Friction factor coefficients for all geometries–all clearances: (a) Geo1, (b) Geo2, (c) Geo3, (d) Geo4, (e) Geo5, and (f) Geo6

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Fig. 7

Friction factor evolution for Geo2 versus (a) Reynolds number, (b) Mach number, and (c) corrected Mach number

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Fig. 8

Effect of cell depth

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Fig. 9

Effect of cell width and orientation—H/H0 = 1

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Fig. 10

Frequency spectra analysis for Geo4—H/H0 = 3.5

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Fig. 11

Frequency peaks versus velocities

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Fig. 12

Frequency peaks versus velocities to cell width ratio

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Fig. 13

Acoustic pressure of first four longitudinal eigenmodes for Geo4: (a) mode I—f = 146.4 Hz, (b) mode II—f = 246.4 Hz, (c) mode III—f = 370.9 Hz, and (d) mode IV—f = 504.7 Hz

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Fig. 14

Friction factor distribution for Geo4

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Fig. 15

Friction factor distribution for Geo4 and Geo5

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Fig. 16

Acoustic pressure oscillations

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Fig. 17

Effect of clearance on maximum acoustic pressure oscillations for Geo6

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Fig. 18

Strouhal experiments and correlation: (a) Geo2, (b) Geo4, (c) Geo5, and (d) Geo6

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Fig. 19

Strouhal number from experiment and correlation for Geo2

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Fig. 20

Friction factor averaged (smooth and honeycomb side) and only relative to the honeycomb side

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Fig. 21

Comparison with rotating seal: (a) mass flow and (b) error

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