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Research Papers: Other (Seals, Manufacturing)

Phase Change and Choked Flow Effects on Rotordynamic Coefficients of Cryogenic Annular Seals

[+] Author and Article Information
Mohamed Amine Hassini

Institut Pprime,
UPR3346 CNRS,
Université de Poitiers,
Poitiers, 86000, France;
Centre National d’études Spatiales,
CNES-DLA, Paris, 75612, France

Mihai Arghir

Institut Pprime,
UPR3346 CNRS,
Université de Poitiers,
Poitiers, 86000, France

However, in annular seals, the radial clearance is constant or very slowly varying, so it is very unlikely that the film height effects could accelerate the compressible flow beyond the sonic threshold.

For a pressure of 1.8MPa near the temperature of saturation, ρl936kg/m3, ρg65kg/m3, μl8.7×10-5Pa·s, μg1.1×10-5Pa·s, Cp,l2kJ/kg/K, Cp,g1.3kJ/kg/K, kl0.1W/m2/K.

Contributed by the Tribology Division of ASME for publication in the Journal of Tribology. Manuscript received August 29, 2012; final manuscript received April 25, 2013; published online June 18, 2013. Assoc. Editor: Luis San Andres.

J. Tribol 135(4), 042201 (Jun 18, 2013) (9 pages) Paper No: TRIB-12-1140; doi: 10.1115/1.4024376 History: Received August 29, 2012; Revised April 25, 2013

The present work deals with the numerical analysis of phase change effects and choked flow on the rotordynamic coefficients of cryogenic annular seals. The analysis is based on the “bulk flow” equations, with the energy equation written for the total enthalpy, and uses an estimation of the speed of sound that is valid for single- or two-phase flow as well. The numerical treatment of choked flow conditions is validated by comparisons with the experimental data of Hendricks (1987, “Straight Cylindrical Seal for High-Performance Turbomachines,” NASA Technical Paper No. 1850) obtained for gaseous nitrogen. The static characteristics and the dynamic coefficients of an annular seal working with liquid or gaseous oxygen are then investigated numerically. The same seal was used in previous analyses performed by Hughes et al. (1978, “Phase Change in Liquid Face Seals,” ASME J. Lubr. Technol., 100, pp. 74–80), Beatty and Hughes (1987, “Turbulent Two-Phase Flow in Annular Seals,” ASLE Trans., 30(1), pp. 11–18), and Arauz and San Andrés (1998, “Analysis of Two Phase Flow in Cryogenic Damper Seals. Part I: Theoretical Model,” ASME J. Tribol., 120, pp. 221–227 and 1998, “Analysis of Two Phase Flow in Cryogenic Damper Seals. Part 2: Model Validation and Predictions,” ASME J. Tribol., 120, pp. 228–233). The flow in the seal is unchoked, and rotordynamic coefficients show variations, with the excitation frequency depending if the flow is all liquid, all gas, or a liquid-gas mixture. Finally, the pressure ratio and length of the previous seal are changed in order to promote flow choking in the exit section. The rotordynamic coefficients calculated in this case show a dependence on the excitation frequency that differ from the unchoked seal.

Copyright © 2013 by ASME
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References

Figures

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Fig. 1

Schematic view of the pressure drop in an annular seal

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Fig. 2

Analytical pressure variation and Mach number in a narrow channel

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Fig. 3

Variation of the pressure along a fully eccentered N2 annular seal

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Fig. 5

Inlet pressure versus inlet temperature

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Fig. 6

Fluid quality at the seal exit section

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Fig. 7

Real part of the direct impedance versus excitation frequency ((L): all liquid, (L → G): liquid-gas mixture (liquid dominant), (G–L): liquid-gas mixture (gas dominant), (G): all gas)

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Fig. 8

Direct damping versus excitation frequency ((L): all liquid, (L → G): liquid-gas mixture (liquid dominant), (G–L): liquid-gas mixture (gas dominant), (G): all gas)

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Fig. 9

Real part of the cross-coupling impedance versus excitation frequency ((L): all liquid, (L → G): liquid-gas mixture (liquid dominant), (G–L): liquid-gas mixture (gas dominant), (G): all gas)

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Fig. 10

Cross-coupling damping versus excitation frequency ((L): all liquid, (L → G): liquid-gas mixture (liquid dominant), (G–L): liquid-gas mixture (gas dominant), (G): all gas)

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Fig. 11

Real part of the direct and cross-coupled impedances versus excitation frequency ((G–L): liquid-gas mixture (gas dominant), (G): all gas)

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Fig. 12

Direct and cross-coupling damping versus excitation frequency ((G–L): liquid-gas mixture (gas dominant), (G): all gas)

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Fig. 13

Critical mass and whirl frequency ratio versus total inlet temperature

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Fig. 14

Fluid quality and speed of sound in the axial direction

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Fig. 15

Mach number and axial velocity in the axial direction

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Fig. 16

Static pressure and enthalpy variation in the axial direction

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Fig. 17

Temperature and density in the axial direction

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Fig. 18

Stiffness coefficients versus excitation frequency (choked flow)

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Fig. 19

Damping coefficients versus excitation frequency (choked flow)

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