Effect of Frequency Excitation on Force Coefficients of Spiral Groove Gas Seals

1999 ◽  
Vol 121 (4) ◽  
pp. 853-861 ◽  
Author(s):  
Nicole Zirkelback ◽  
Luis San Andre´s
Keyword(s):  
Finite Element ◽  
Compressible Fluid ◽  
Fluid Model ◽  
Dynamic Performance ◽  
Excitation Frequency ◽  
Spiral Groove ◽  
Thrust Bearings ◽  
Force Coefficients ◽  
Frequency Excitation ◽  
Gas Seals

An analysis for compressible fluid spiral groove thrust bearings (SGTBs) and face seals (SGFSs) is presented. Zeroth- and first-order equations rendering the static and dynamic performance of SGFSs, respectively, are solved using the finite element method with a successive approximation scheme. Comparison of the present isothermal compressible fluid model for static and dynamic SGTB and SGFS performance validates previous narrow groove theory, finite difference, and finite element analyses. A discussion follows to indicate the importance of using a small number of grooves to prevent instabilities from negative damping in SGTBs and SGFSs when pressurization is lost. Force coefficients are shown to reach asymptotic limits as the axial excitation frequency increases.

Finite Element Analysis of Grooved Gas Thrust Bearings and Grooved Gas Face Seals

1993 ◽  
Vol 115 (3) ◽  
pp. 348-354 ◽  
Author(s):  
D. Bonneau ◽  
J. Huitric ◽  
B. Tournerie
Keyword(s):  
Finite Element ◽  
Reynolds Equation ◽  
Weak Form ◽  
Oscillating Solution ◽  
Element Analysis ◽  
Finite Element Program ◽  
Thrust Bearings ◽  
Face Seals ◽  
Element Program ◽  
Gas Seals

A finite element method enabling the Reynolds equation solution for any face geometry of gas thrust bearing or of gas seal is presented. Difficulties due to thickness discontinuities are reduced by integration by parts of the terms involving derivatives. The weak form of the finite element Reynolds equation is then solved and the nonlinearity of the equation leads to the use of Newton-Raphson procedure. The process is fast convergent. The problem of oscillating solution is solved by the use of an upwind procedure. Some numerical examples show the accuracy and efficiency of the procedures. It is shown that the developed finite element program provides a numerical tool, more efficient than the method used until now, for the grooved gas seals design.

Rotordynamic Force Coefficients of Bubbly Mixture Annular Pressure Seals

2011 ◽  
Author(s):  
Luis San Andre´s
Keyword(s):  
Power Loss ◽  
Volume Fraction ◽  
Dynamic Stiffness ◽  
Excitation Frequency ◽  
Experimental Program ◽  
Dynamic Force ◽  
Force Coefficients ◽  
Large Expansion ◽  
Gas Seals ◽  
Gas Volume

As oil fields deplete, in particular in deep sea reservoirs, pump and compression systems work under more strenuous conditions with gas in liquid and liquid in gas mixtures, mostly inhomogeneous. Off-design operation affects system overall efficiency and reliability, including penalties in leakage and rotordynamic performance of secondary flow components, namely seals. The paper details a bulk-flow model for annular damper seals operating with gas in liquid mixtures. The analysis encompasses all-liquid and all-gas seals, as well as seals lubricated with homogenous (bubbly) mixtures, and predicts the static and dynamic force response of mixture lubricated seals; namely: leakage, power loss, reaction forces and rotordynamic force coefficients, etc., as a function of the mixture volume fraction (βS), supply and discharge pressures, rotor speed, whirl frequency, etc. A seal example with a Nitrogen gas mixed with light oil is analyzed. The large pressure drop (70 bar) causes a large expansion of the gas within the seal even for (very) small gas volume fractions (βS). Predictions show leakage and power loss decrease as β → 1; albeit at low βS (<0.3) (re)laminarization of the flow and an apparent increase in mixture viscosity, produce a hump in power loss. Cross-coupled stiffnesses and direct damping coefficients decrease steadily with increases in the gas volume fraction; however some anomalies are apparent when the flow turns laminar. Mixture lubricated seals show frequency dependent force coefficients. The equivalent damping decreases above and below βS∼0.10. The direct stiffness coefficients show atypical behavior: a low βS = 0.1 produces stiffness hardening as the excitation frequency increases. Recall that an all liquid seal has a dynamic stiffness softening as frequency increases due to the apparent fluid mass. The predictions call for an experimental program to quantify the static and dynamic forced performance of annular seals operating with (bubbly) mixtures and to validate the current predictive model results.

An Efficient Finite Element Procedure for Analysis of High-Speed Spiral Groove Gas Face Seals

2000 ◽  
Vol 123 (1) ◽  
pp. 205-210 ◽  
Author(s):  
Marco Tulio C. Faria
Keyword(s):  
Finite Element ◽  
High Speed ◽  
Dynamic Performance ◽  
Dynamic Force ◽  
Spiral Groove ◽  
Weighted Residual Method ◽  
New Class ◽  
High Speeds ◽  
Face Seals ◽  
Finite Element Procedure

An efficient and accurate finite element procedure is specially devised to analyze the performance of gas-lubricated spiral groove face seals operating at high speeds. The procedure is based on the Galerkin weighted residual method with a new class of high-order shape functions, which are derived from an approximate solution to the nonlinear Reynolds equation within an element. Static and dynamic performance characteristics, such as seal opening force, flow leakage and frequency-dependent dynamic force coefficients, are determined to study the effects of high speeds on the behavior of spiral groove gas face seals.

Numerical Comparison of Rotordynamic Characteristics for a Fully-Partitioned Pocket Damper Seal and a Labyrinth Seal With High Positive and Negative Inlet Preswirl

2015 ◽  
Author(s):  
Zhigang Li ◽  
Jun Li ◽  
Zhenping Feng
Keyword(s):  
Excitation Frequency ◽  
Cross Coupling ◽  
Labyrinth Seal ◽  
Numerical Results ◽  
Numerical Comparison ◽  
Crossover Frequency ◽  
Frequency Dependent ◽  
Force Coefficients ◽  
Coupling Stiffness ◽  
Gas Seals

Pocket damper seals are used as replacements for labyrinth seals in high-pressure centrifugal compressors at the balance piston location or center seal location to enhance rotordynamic stability. A concern exists that this enhanced stability will be lost at high positive inlet preswirl. Numerical results of frequency-dependent rotordynamic force coefficients and leakage flow rates were presented and compared for a fully-partitioned pocket damper seal (FPDS) and a labyrinth seal at high positive and negative inlet preswirl, using a proposed transient CFD method based on the multi-frequency elliptical orbit whirling model. The negative preswirl indicates a fluid swirl in a direction opposite to rotor rotation at seal inlet. Both seals have identical diameter and sealing clearance. The full 3D concentric CFD model and mesh were built for the labyrinth seal and FPDS, respectively. The accuracy and availability of the present transient CFD numerical method were demonstrated with the experiment data of frequency-dependent rotordynamic coefficients of the labyrinth seal and FPDS at zero and high positive preswirl conditions. The numerical boundary conditions include two high positive preswirl, two high negative preswirl and a zero preswirl. Numerical results show that the effect of inlet preswirl on the direct force coefficients is weak, but the effect on the cross-coupling stiffness and effective damping is dramatic. Both two seals possess negative effective damping at lower excitation frequencies due to positive preswirl, and the crossover frequency of effective damping term increases with increasing positive preswirl. Negative preswirl produces negative cross-coupling stiffness and positive effective damping over the whole excitation frequency range. Increasing negative preswirl is a stabilizing factor for annular gas seals which results in a significant increase in the effective damping and a decrease in the crossover frequency. It is desirable to reduce the inlet preswirl to zero or even negative through applications of negative-swirl brakes and negative injection devices.

Rotordynamic Force Coefficients of Bubbly Mixture Annular Pressure Seals

2011 ◽  
Vol 134 (2) ◽  
Author(s):  
Luis San Andrés
Keyword(s):  
Power Loss ◽  
Volume Fraction ◽  
Dynamic Stiffness ◽  
Excitation Frequency ◽  
Experimental Program ◽  
Dynamic Force ◽  
Force Coefficients ◽  
Large Expansion ◽  
Gas Seals ◽  
Gas Volume

As oil fields deplete, in particular in deep sea reservoirs, pump and compression systems work under more strenuous conditions with gas in liquid and liquid in gas mixtures, mostly inhomogeneous. Off-design operation affects system overall efficiency and reliability, including penalties in leakage and rotordynamic performance of secondary flow components, namely seals. The paper details a bulk-flow model for annular damper seals operating with gas in liquid mixtures. The analysis encompasses all-liquid and all-gas seals, as well as seals lubricated with homogenous (bubbly) mixtures, and predicts the static and dynamic force response of mixture lubricated seals; namely: leakage, power loss, reaction forces, and rotordynamic force coefficients, etc., as a function of the mixture volume fraction (βS), supply and discharge pressures, rotor speed, whirl frequency, etc. A seal example with a nitrogen gas mixed with light oil is analyzed. The large pressure drop (70 bar) causes a large expansion of the gas within the seal even for (very) small gas volume fractions (βS). Predictions show leakage and power loss decrease as β→1; albeit at low βS (< 0.3) (re)laminarization of the flow and an apparent increase in mixture viscosity, produce a hump in power loss. Cross-coupled stiffnesses and direct damping coefficients decrease steadily with increases in the gas volume fraction; however, some anomalies are apparent when the flow turns laminar. Mixture lubricated seals show frequency-dependent force coefficients. The equivalent damping decreases above and below βS ∼ 0.10. The direct stiffness coefficients show atypical behavior: a low βS = 0.1 produces stiffness hardening as the excitation frequency increases. Recall that an all liquid seal has a dynamic stiffness softening as frequency increases due to the apparent fluid mass. The predictions call for an experimental program to quantify the static and dynamic forced performance of annular seals operating with (bubbly) mixtures and to validate the current predictive model results.

Numerical Comparison of Rotordynamic Characteristics for a Fully Partitioned Pocket Damper Seal and a Labyrinth Seal With High Positive and Negative Inlet Preswirl

2015 ◽  
Vol 138 (4) ◽  
Author(s):  
Zhigang Li ◽  
Jun Li ◽  
Zhenping Feng
Keyword(s):  
Excitation Frequency ◽  
Cross Coupling ◽  
Labyrinth Seal ◽  
Numerical Results ◽  
Numerical Comparison ◽  
Crossover Frequency ◽  
Frequency Dependent ◽  
Force Coefficients ◽  
Coupling Stiffness ◽  
Gas Seals

Pocket damper seals (PDSs) are used as replacements for labyrinth seals in high-pressure centrifugal compressors at the balance-piston location or center seal location to enhance rotordynamic stability. A concern exists that this enhanced stability will be lost at high positive inlet preswirl. Numerical results of frequency-dependent rotordynamic force coefficients and leakage flow rates were presented and compared for a fully partitioned PDS (FPDS) and a labyrinth seal at high positive and negative inlet preswirl, using a proposed transient computational fluid dynamics (CFD) method based on the multifrequency elliptical orbit whirling model. The negative preswirl indicates a fluid swirl in a direction opposite to rotor rotation at seal inlet. Both seals have identical diameter and sealing clearance. The full 3D concentric CFD model and mesh were built for the labyrinth seal and FPDS, respectively. The accuracy and availability of the present transient CFD numerical method were demonstrated with the experiment data of frequency-dependent rotordynamic coefficients of the labyrinth seal and FPDS at zero and high positive preswirl conditions. The numerical boundary conditions include two high positive preswirl, two high negative preswirl, and a zero preswirl. Numerical results show that the effect of inlet preswirl on the direct force coefficients is weak, but the effect on the cross-coupling stiffness and effective damping is dramatic. Both seals possess negative effective damping at lower excitation frequencies due to positive preswirl, and the crossover frequency of effective damping term increases with increasing positive preswirl. Negative preswirl produces negative cross-coupling stiffness and positive effective damping over the whole excitation frequency range. Increasing negative preswirl is a stabilizing factor for annular gas seals, which results in a significant increase in the effective damping and a decrease in the crossover frequency. It is desirable to reduce the inlet preswirl to zero or even negative through applications of negative-swirl brakes and negative injection devices.

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