Advanced Analysis of Multi-Ring Liquid Seals

Test results are presented for laminar-flow seals that are representative of buffered-flow oil seals in centrifugal compressors. The seals are short (L∕D≅0.21), with a diameter of 117mm and a clearance-to-radius ratio 0.0007. A smooth seal, a seal with one central groove, and a seal with three grooves were tested. Groove geometries employed are representative of industrial practice for compressors with a groove-depth to clearance ratio on the order of 6. Tests were conducted at 4000, 7000, and 10,000rpm shaft speed with delta pressures across the seals of 21, 45, and 69bars. For all cases, the flow was laminar. The seals were tested from a centered position out to an eccentricity ratio of 0.7. Static data included leakage and equilibrium loci for a range of loads. Direct and cross-coupled stiffness and damping coefficients and direct mass coefficients were determined from dynamic tests. For the smooth seal, comparisons between measurements and predictions were reasonable for the direct and cross-coupled stiffness and damping coefficients; however, measured added mass coefficients were roughly ten times larger than predicted. Predictions for the grooved seals from a “deep-groove” model that assumed zero pressure oscillations in the grooves greatly over predicted the influence of the grooves. In a centered position, smooth and grooved seals had comparable leakage performance. At higher eccentricity ratios, the grooved seals leaked modestly more. For eccentricity ratios less than approximately 0.3, the grooved seals and the smooth seal had qualitatively similar static and dynamic characteristics. In terms of cross-coupled stiffness coefficients, the grooved seals were less stable than the smooth seal at eccentricity ratios greater than approximately 0.5 but had significantly lower cross-coupled coefficients at reduced eccentricity ratios between zero and 0.3. A grooved centered seal is more stable than a smooth centered seal. The smooth seal had higher damping than the grooved seals and had moderately better centering capabilities.

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Analysis of High Pressure Liquid Seal Ring Distortion and Stability Using Finite Element Methods

Baheti¹,

Kirk

1999

Journal of Tribology

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The evaluation of floating bushing ring oil seals is of great importance for designs of high pressure centrifugal compressors. This is a result of their enhanced damping capacity at low speeds and their strong destabilizing action at speeds in excess of twice the compressor first critical speed. Accurate prediction of oil seal leakage and exit temperature is very important from the standpoint of the pump and cooler selection for the seal oil console. The previous research has performed thermohydrodynamic (THD) analysis of bushing seal rings with various geometries. The current work is to evaluate the influence of the mechanical deformation on the thermohydrodynamic analysis of the bushing seal ring. The finite element method is used to predict the mechanical deformation of the bushing seal ring due to oil pressure and to solve the nonlinear and coupled Reynolds and energy equations for the pressure and temperature distributions, respectively. The perturbation technique is used to evaluate the stiffness and damping coefficients of the oil seals. Eigenvalue analysis is performed to study the dynamic stability of the compressor rotor. Results comparing the seal leakage, seal oil outlet temperatures, stiffness and damping coefficients, growth factors and damped natural frequencies from the THD analyses with and without the influence of the mechanical deformation of the bushing seal ring are presented. The results indicate that under high pressure conditions the influence of the mechanical deformation of the bushing seal ring on the seal performance is very significant.

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Advanced Analysis of Multi-Ring Liquid Seals

Cited by 4 publications

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Finite Element Thermohydrodynamic Analysis of Two-Lobe Oil Seals Used in High Pressure Centrifugal Compressors

Finite Element Thermohydrodynamic Analysis of Two-Lobe Oil Seals Used in High Pressure Centrifugal Compressors

Rotordynamic-Coefficients and Static (Equilibrium Loci and Leakage) Characteristics for Short, Laminar-flow Annular Seals

Analysis of High Pressure Liquid Seal Ring Distortion and Stability Using Finite Element Methods

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