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Research Papers: Internal Combustion Engines

Theoretical Analysis of Brush Seals Leakage Using Local Computational Fluid Dynamics Estimated Permeability Laws

[+] Author and Article Information
Lilas Deville

CNES,
Direction des Lanceurs
75612 Paris/PPRIME Institute,
UPR CNRS 3346 Université de Poitiers,
ENSMA ISAE,
Chasseneuil Futuroscope 86962, France

Mihai Arghir

PPRIME Institute,
UPR CNRS 3346 Université de Poitiers,
ENSMA ISAE,
Chasseneuil Futuroscope 86962, France

Contributed by the IC Engine Division of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received March 11, 2017; final manuscript received September 14, 2017; published online February 13, 2018. Assoc. Editor: Philip Bonello.

J. Eng. Gas Turbines Power 140(6), 062803 (Feb 13, 2018) (12 pages) Paper No: GTP-17-1095; doi: 10.1115/1.4038469 History: Received March 11, 2017; Revised September 14, 2017

Brush seals are a mature technology that has generated extensive experimental and theoretical work. Theoretical models range from simple correlations with experimental results to advanced numerical approaches coupling the bristles deformation with the flow in the brush. The present work follows this latter path. The bristles of the brush are deformed by the pressure applied by the flow, by the interference with the rotor and with the back plate. The bristles are modeled as linear beams but a nonlinear numerical algorithm deals with the interferences. The brush with its deformed bristles is then considered as an anisotropic porous medium for the leakage flow. Taking into account, the variation of the permeability with the local geometric and flow conditions represents the originality of the present work. The permeability following the principal directions of the bristles is estimated from computational fluid dynamics (CFD) calculations. A representative number of bristles are selected for each principal direction and the CFD analysis domain is delimited by periodicity and symmetry boundary conditions. The parameters of the CFD analysis are the local Reynolds number and the local porosity estimated from the distance between the bristles. The variations of the permeability are thus deduced for each principal direction and for Reynolds numbers and porosities characteristic for brush seal. The leakage flow rates predicted by the present approach are compared with experimental results from the literature. The results depict also the variations of the pressures, of the local Reynolds number, of the permeability, and of the porosity through the entire brush seal.

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References

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Figures

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Fig. 1

Schematic representation of a brush seal

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Fig. 2

Simplified representation of the simulated bristles pack

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Fig. 3

Cross section of the simulated cell

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Fig. 4

Local and global coordinates systems

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Fig. 5

Discretization of the bristles

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Fig. 6

View of two interacting bristles: (a) interfering bristles before correction and (b) contacting bristles after correction

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Fig. 7

Calculation of the brush porosity

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Fig. 8

Domain for the flow calculation

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Fig. 9

Calculation of the pressure forces on the bristles

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Fig. 10

Three CFD models for the pressure drop calculations along x (a), y (b), and z (c) axis

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Fig. 11

Examples of meshes

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Fig. 12

Pressure drops along x axis

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Fig. 13

Pressure drops along y axis

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Fig. 14

Pressure drops along z axis

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Fig. 15

Comparison of the calculated pressure drops along x axis with the literature [6,9,11]

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Fig. 16

Comparison of the calculated pressure drops along y axis with the literature [6,9,11]

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Fig. 17

Comparison of the calculated pressure drops along z axis with the literature [6,9,11]

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Fig. 18

Summary of the calculation method

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Fig. 19:

Comparison of the calculated mass flow rates with the literature [20]

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Fig. 20

Maximum brush porosity

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Fig. 21

Calculated porosity field in a section of the brush (jmax = 7, e = 1.2 μm and ΔP = 3 bar)

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Fig. 22

Calculated pressure field in a section of the brush (jmax = 7, e = 1.2 μm and ΔP = 3 bar)

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Fig. 23

Neutral line of the deformed bristles, in the (y,z) plane

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Fig. 24

Reynolds number in a section of the brush (jmax = 8, e = 1.2 μm and ΔP = 1 bar)

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Fig. 25

Reynolds number in a section of the brush (jmax = 8, e = 2.5 μm and ΔP = 3 bar)

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Fig. 26

Calculation of the number of bristles in the axial direction from the bristle pack density

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