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Research Papers: Gas Turbines: Structures and Dynamics

Experimental Analysis of Floating Ring Annular Seals and Comparisons With Theoretical Predictions

[+] Author and Article Information
Antoine Mariot

CNES/PPRIME Institute,
CNRS, ENSMA ISAE,
University of Poitiers,
Chasseneuil Futuroscope 86962, France

Mihai Arghir

PPRIME Institute,
CNRS, ENSMA ISAE,
University of Poitiers,
Chasseneuil Futuroscope 86962, France

Pierre Hélies

Space Engines Division,
SNECMA,
Vernon 27208, France

Jérôme Dehouve

Direction des Lanceurs,
CNES,
Paris 75612, France

Contributed by the Structures and Dynamics Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received July 20, 2015; final manuscript received August 7, 2015; published online October 13, 2015. Editor: David Wisler.

J. Eng. Gas Turbines Power 138(4), 042503 (Oct 13, 2015) (9 pages) Paper No: GTP-15-1347; doi: 10.1115/1.4031347 History: Received July 20, 2015; Revised August 07, 2015

Floating ring annular seals represent one of the solutions for controlling leakage in high-speed rotating machinery. They are generally made of a carbon ring mounted in a steel ring for preserving their integrity. Low leakage is ensured by the small clearance of the annular space between the carbon ring and the rotor. Under normal operating conditions, the ring must be able to “float” on the rotor in order to accommodate its vibration. Impacts between the carbon ring and the rotor may occur when the annular seal is locked up against the stator and the amplitude of rotor vibrations are larger than the radial clearance. This situation is prohibited because it rapidly leads to the destruction of the carbon ring. The present work presents experimental results obtained for floating ring annular seals of 38 mm, tandem mounted in a buffer seal arrangement. The rotation speed was comprised of between 50 Hz and 350 Hz, and maximum pressure drop was 7 bar. For these operating conditions, the floating ring follows the rotor vibrations without any impacts. Comparisons were made with a theoretical model based on the equations of motion of the floating ring driven by mass inertia forces, hydrostatic forces in the (main) annular seal, and by friction forces on its radial face (also named the “nose” of the seal). The friction coefficient on the nose of the floating ring was estimated from Greenwood and Williamson's model for mixed lubrication. The present analysis validates the theoretical model used for predicting the dynamic response of the floating ring for a given rotor motion.

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References

Figures

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Fig. 7

Metrology (left) and spectral analysis (right) of the test section of the rotor

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Fig. 6

Theoretical eigenmodes of the rotor guided by the hydrostatic Lomakin bearings (KLomakin=3.5×107 N/m, zero damping)

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Fig. 5

Buffer seal support mounted on the test rig

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Fig. 4

Buffer seal arrangement

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Fig. 3

Ensemble view of the test rig

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Fig. 2

Forces acting on the nose of the floating ring

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Fig. 1

Simplified model of a floating ring seal

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Fig. 10

Typical trajectories of the rotor (top) and of the floating ring (bottom) and their spectral content for Ω = 350 Hz and Psupply = 11 bar, 25 g mm unbalance

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Fig. 15

Experimental and theoretical synchronous amplitudes of the floating ring

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Fig. 8

Trajectories of the rotor left section (a), of the floating rings 1–4 ((b)–(e)), and of the rotor right section (f) for Ω = 150 Hz and Psupply = 2 bar, no additional unbalance

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Fig. 9

Trajectories of the rotor left section (a), of the floating rings 1–4 ((b)–(e)), and of the rotor right section (f) for Ω = 350 Hz and Psupply = 11 bar, 25 g mm unbalance

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Fig. 12

Measured and corrected trajectory of the rotor for Ω = 350 Hz and Psupply = 0.5 bar, no additional unbalance

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Fig. 13

Trajectories of the floating ring, Ω = 250 Hz and small rotor amplitudes

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Fig. 14

Trajectories of the floating ring, Ω = 350 Hz and large rotor amplitudes

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Fig. 11

Variation of the equivalent friction coefficient

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Fig. 16

Relative position of the rotor and of the floating ring

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Fig. 17

Minimum film thickness and phase angle between the rotor and the floating ring

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