Spiral Groove Face Seals Research Articles

A heat transfer model for thermal distortions in high speed spiral groove gas lubricated face seals

The thermal distortions of seal face caused by heat transfer directly affect the stability of seal operation. Here, a heat transfer analysis model of spiral groove gas face seal is established taking account of gas compressibility and choked flow effect. Then, a thermoelastohydrodynamic lubrication (TEHL) analysis is carried out based on the proposed heat transfer model, frictional heat flux, surface conduction heat flux, and film adsorption heat flux are calculated, and face distortions are also analyzed under different operating parameters including rotational speed, seal temperature and seal pressure. It is shown that, the adsorption heat induced by gas expansion makes the film cooling, which often leads complex temperature distributions and plays an important and non-ignored role in thermal distortions. For the spiral groove face seal, the increase of seal pressure and rotational speed makes the adsorption heat increase significantly due to pumping effect of grooves. The more important is that the thermal distortions may be controlled by changing seal width. Here, for the spiral groove face seal, the clearance can transfer divergent to convergent with increasing seal width from 5 mm to 13.1 mm. This provides a potential way for distortion control in gas face seal design.

Thermo-Hydrodynamic Analysis of Low-Temperature Supercritical Helium Spiral-Grooved Face Seals: Large Ambient Temperature Gradient

Hhighly efficient and reliable sealing technology is essential to improve the efficiency of precooled aeroengines. To explore the effects of large ambient temperature gradients on the sealing performance, the thermo-hydrodynamic characteristics of a supercritical helium spiral-grooved face seal were studied numerically, under low-temperature conditions. Considering the real gas effect of helium, the thermal deformations of the seal were analyzed numerically, under different temperature gradients. Additionally, the distributions of the pressure, temperature, and film thickness of the gas film were calculated, and the sealing performances of the seal under a wide range of working conditions were evaluated simultaneously. Results showed that a turning point occurred at the sealing pressure of 1.6 MPa in both the dynamic pressure effect and temperature rise of the gas film under the ambient-temperature gradient, leading to the transformation of the sealing gap, from convergent to divergent. The temperature gradient contributed to decreasing the thermal deformation and improving the sealing performance of the face seal. As the temperature gradient increased, although a mutational phenomenon existed near the sealing temperature of 250 K with both the dynamic pressure effect and the temperature rise, the variation of the opening force was within 120 N and the leakage was more than halved, indicating the broad application prospects of gas face seals in precooled aeroengine systems.

Elastic deformation of liquid spiral groove face seals operating at high speeds and low pressure

The uneven distribution of fluid pressure in the spiral groove area leads to the elastic deformation of the seal faces, which not only affects the sealing performance but also affects the running stability. In this paper, a numerical model of a high-speed spiral groove liquid face seal is proposed with the consideration of elastic deformation and cavitation medium compressibility. The novelty of this study is that the pressure of the cavitation region is modeled as an uneven distribution rather than as a constant. This uneven pressure distribution of sealing surfaces is generally regarded to have an influence on face deformation. Based on the assumption that the fluid exists at a complete gas state in the cavitation, the elastic deformation and pressure distribution of sealing surfaces are calculated. The influence of elastic deformation on sealing performance is further investigated. Results show that the elastic deformation of sealing surfaces and cavitation effect has a significant influence on the stability of sealing clearance, which may produce a negative effect on the sealing performance of liquid face seals. The face deformation causes a divergent gap between two seal faces. With the increase of rotational speed, the elastic deformation of sealing surfaces reduces at low seal pressure but increases at higher seal pressure, which may influence the cavitation behavior and pressure distribution of surfaces. Furthermore, the sealing performance of spiral groove liquid face seal becomes more complicated because of the coupling effect of cavitation effect and elastic deformation. The changing trend of sealing performance is different under various seal clearance and seal pressure. The obtained results may provide guidance for the future design of liquid face seals in engineering applications under high-speed conditions.

Thermoelastohydrodynamic characteristics of supercritical CO2 spiral groove face seals

PurposeThe purpose of this study is to determine the sealing performance of face seals by numerical analysis of thermoelastohydrodynamic characteristics of supercritical CO2 (S-CO2) spiral groove face seals in the supercritical regime.Design/methodology/approachThe spiral groove face seal was used as the research object. The distribution of lubricating film pressure and temperature was analysed by solving the gas state, Reynolds and energy equations using the finite difference method. Furthermore, the influence law of sealing performance was obtained.FindingsClose to the critical temperature of S-CO2, face distortions produced by increasing pressure lead to divergent clearance and resulted in reduced opening force. In the state of S-CO2, the face distortions generated by increasing seal temperature lead to convergent clearance, which enhances the opening force. In addition, near the critical temperature of S-CO2, the opening force may be reduced by 10%, and the leakage rate of the seal sharply increases by a factor of four.Originality/valueThe thermoelastohydrodynamic characteristics of supercritical CO2 face seals are illustrated considering the actual gas effect including compressibility, heat capacity and viscosity. Face distortions and sealing performance were calculated under different seal pressures and seal temperatures in the supercritical regime, as well as with N2 for comparison.Peer reviewThe peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-05-2020-0169/

Spiral Groove Face Seal Behavior and Performance in Liquid Lubricated Applications

ABSTRACTA series of experiments was conducted to study the behavior and performance of a spiral groove mechanical face seal in liquid lubricated applications. The seal's ability to contain water from ambient to near saturation conditions was tested. A comparison of experimental results with a numerical solution of the Reynolds equation under isothermal conditions was done. Two-phase and non-laminar flows were observed because of high speed, high temperature and high film thickness. Different lubrication regimes, such as mixed and hydrodynamic, were also reached. The results show that the spiral groove face seal can work for a large operating range with a lower friction factor but a higher leakage than the smooth face seal configuration.

A Semi-Analytical Model of Spiral-Groove Face Seals: Correction and Extension

ABSTRACTThis article presents a semi-analytical model of spiral-groove face seals. Based on Muijderman's spiral-groove bearing theory for parallel faces, a one-dimensional radial discretization method is proposed to process the radial variations of different parameters of face seals. For each discrete element, the geometric parameters of the faces (e.g., film thickness, groove shape) and the physical parameters of the lubricant (e.g., density, viscosity) can be assigned to reflect the radial nonuniformity of these parameters. Furthermore, a correction of the end effect is introduced to improve the model's precision. Errors in this model under various operating conditions and with different design parameters are analyzed by comparison with the traditional one-dimensional difference model and the two-dimensional numerical model. The calculation results indicate that the proposed model is more accurate than the traditional one-dimensional difference model under various conditions. Furthermore, it is shown that the proposed model could be applied to the analysis and design of face seals with different types of grooves and lubricants as well as different radial nonuniformities in their geometric and physical parameters. These extended applications of the proposed model could provide good approximations to the two-dimensional numerical results. This semi-analytical model has the benefits of an analytical method (e.g., simple preprocessing, high efficiency, and the ability to manage large-scale parameter optimization) and of a numerical method (e.g., the ability to be applied to extended applications of face seals with shallow grooves).

Thermoelastohydrodynamic Gas Lubrication of Spiral-Groove Face Seals: Modeling and Analysis of Vapor Condensation

ABSTRACTVapor condensation in gas lubrication of high-pressure spiral-groove face seals is analyzed in this article. A mathematical model of vapor condensation elastohydrodynamic lubrication (EHL) is developed taking into account gas humidity and thermoelastic deformation of seal rings. Vapor condensation is numerically predicted at high speed and pressure. It is found that vapor condensation usually occurs in the sealing dam region, where the lubrication state changes from gas lubrication to gas–liquid lubrication. The vapor condensation rate increases with an increase in humidity and seal pressure. Under high-pressure conditions, seal clearance has a significant influence on the vapor condensing rate but the rotational speed does not.

Thermoelastohydrodynamic Behavior of Gas Spiral Groove Face Seals Operating at High Pressure and Speed

A numerical modeling of thermoelastohydrodynamic gas spiral groove face seal behavior is presented. Temperature fields of the fluid film and the seal rings are computed, as they are the elastic and thermal distortions of the rings. Numerical analysis is carried out on a gas spiral groove face seal taking into account of choked flow effect. Analysis results show that both elastic and thermal distortions induce strong influence on the geometry of the fluid film, forming obvious divergent clearance which leads to significant decrease of minimum equilibrium clearance, exceeding 50% in degree. Thermal distortion may induce the same influence degree as elastic distortion on the minimum equilibrium clearance in high pressure cases, but the rotation speed has no obvious influence on the minimum clearance when both elastic and thermal distortions are considered. The thermal distortion as well as elastic distortion should be concerned in high pressure analysis.

Experimental study on the water lubrication of non-contacting face seals for turbopumps

Purpose – A new type of hydrostatic and hydrodynamic non-contacting face seals has been designed to meet the requirements of lower leakage, longer life and more repeatedly start and stop on shaft seals raised by liquid rocket engine turbopumps. And an experimental study on the performance of the face seal in the actual liquid oxygen turbopump was completed where low-viscosity water was selected as the seal fluid for the sake of safety. The paper aims to discuss these issues. Design/methodology/approach – Different performances of face seals under preset conditions were obtained by repeatedly running tests, and the main performance parameters encompass leakage, fluid film pressure between the faces, operating power, face temperature, and so on. Findings – The results indicate that the designed face seal has a smaller amount of leakage, with a minimum value of 3 ml/s. Furthermore, the designed face seal has been proved to demand lower operating power. Since its operating power changes slightly with different sealed fluid pressures, the new seal can be deployed in the harsh working condition with high pressure or with high speed (greater than 20,000 rpm). However, one proviso is that when liquid is employed as the seal fluid, the groove depth should be relatively deeper (greater than 10 μm). Research limitations/implications – In response to future engineering requirements, study on the controllable spiral-groove face seals to improve the current design is being conducted. Originality/value – The advancement of such non-contacting face seals proffers important insights to the design of turbo-pump shaft seal in a new generation of liquid rocket engine with regard to the requirement of frequent start and stop as well as long life on it.

Design and Experimental Study on the Controllable High-Speed Spiral Groove Face Seals

The spiral groove face seal is a prime candidate for application of the liquid oxygen and liquid hydrogen turbopump. The study investigated the designs of the electro-magnetic loading device (EMLD) and friction torque testing device (FTTD), and their application in the interface experiments of face seals with spiral grooves which used water as the sealing fluid. The seal performance parameters, including face temperature, face friction torque, film pressure at the seal dam, were measured under the static balance position, and the effects of the face closing force, which varied with the axial load generated from the EMLD, on the seal performance were tested under a specific controlled mode. The result indicated that both the pressure at the seal dam and face temperature increased with the rotating speed and that small friction was obtained when the face seal was fully film-lubricated. The separation speed of the controllable seal could also be controlled, which helped seal faces lift off and met the conditions of the face noncontact status. Additionally, with the application of the EMLD and FTTD, seal operation monitoring was rendered possible and a controllable face seal with desirable performance was achieved. The findings of the current study lend great insights into engineering seal design and its applications.

A Theoretical and Experimental Study on Characteristics of Water-Lubricated Double Spiral–Grooved Seals

The spiral-grooved seal is a prime candidate for application to liquid oxygen (LOX) turbopumps. A theoretical model of double spiral–grooved seals dealing with the viscosity–temperature relation is presented. The effect of operating parameters (rotational speed, supply pressure) and configurative parameters (depth of spiral groove) on the basic static characteristics (opening force, leakage, static friction torque, face temperature, and power loss) of double spiral–grooved seals are examined. Comparisons are presented between measurements and theoretical predications for a narrow spiral-grooved face seal with an average diameter of 100 mm, operating at high speed and using water as a test fluid. The theoretical and experimental results indicate that the temperature on seal faces rises and friction torque increases with the speed and supply pressure, and these increases vary slightly with the depth of the spiral groove. These findings lend great theoretical and experimental insights to the design of face seals applied in liquid engine turbopumps.

Theoretical and Experimental Approach of Separation Speed of Spiral Groove Face Seals

The theoretical and analytical model of separation speed of spiral groove face seal is introduced.A mathematical model of non-contacting double narrow spiral grooved seals is presented.The separation speed of double narrow groove face seal with outer spiral grooves and inner herringbone grooves is obtained.The influences of rotation speed and film thickness on the basic static cha- racteristics(opening force,leakage,fiiction torque and power loss)of non-contacting double narrow spiral grooved seals are dis- cussed.Comparisons are presented between the measures and predications of an important parameter(separation speed)for a 100 mm diameter,narrow spiral groove(3 Barn)face seal using water(27℃)as a test fluid.The results show that the non-contacting seal is formed at about 9 kr/min,and its leakage is about 1.2 mL/s.The relative errors between the measured and the predicted separation speed are less than 10%,and the parameter(separation speed)of the face seal is validated.When the rotation speed is higher than separation speed,the face seal is in non-contacting state,which has the low leakage and the long life.These findings provide the theoretical and experimental references for the design of reused face seal applied in the liquid rocket engine turbopumps.

Numerical Modeling of Dynamic Sealing Behaviors of Spiral Groove Gas Face Seals

A numerical model is developed for the dynamic analysis of gas lubricated spiral groove face seals. Effects of the rotor runout, misalignment, face contact, as well as the stiffness and damping of the secondary seal are considered. Seal axial and angular motions and key parameters such as torque, power loss, and flow rate are obtained by a global time integration scheme, which traces the time history of the dynamic sealing behaviors. The analysis of gas film lubrication, face contact, and the seal dynamics is cast as an inverse problem and the solution is obtained iteratively at each time step. Dynamic tracking motion and key sealing characteristics of a representative spiral groove gas seal undergoing transient operations are presented.

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

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 Formulation for the Dynamic Analysis of Spiral-Grooved Gas Face Seals

A numerical formulation is presented for the dynamic analysis of spiral-grooved gas lubricated mechanical face seals with a flexibly mounted stator. Axial and angular modes of motion are considered. Both finite volume and finite element methods are employed for the spatial discretization of the unsteady, compressible form of the Reynolds equation. Self-adapting unwinding schemes are employed in both methods, making them suitable for situations when the compressibility number is high. Both the lubrication analysis and the kinetic analysis are arranged into a single state space form, which makes coupling the two analyses straightforward. The resulting set of equations is solved using a linear multistep ordinary differential equation solver. Examples of the transient response to static stator misalignment and rotor runout are given. Although a properly designed spiral grooved face seal provides good dynamic performance, it is shown that unacceptably large face separation can occur when large angle spiral grooves are employed together with a sealing dam.

Effect of Frequency Excitation on Force Coefficients of Spiral Groove 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.

Reverse Rotation Capability of Spiral-Groove Gas Face Seals

The dry-running spiral groove face seals, used in centrifugal compressors, are known for trouble-free operation and reduced operating and maintenance costs. This type of seal creates a gas film between the faces which prevents contact while running. Generally, the film stiffness of a unidirectional spiral groove seal is much higher than that of a corresponding bidirectional seal. In reverse rotation, however, a spiral-groove seal loses its film stiffness and may even become negative depending on operating pressure and speed as well as the groove design parameters. Some compressors during their operating cycle may run in the reverse direction for short periods of time. This paper describes the analysis, design and testing of a spiral groove seal wit reverse rotation capability. A seal designed for a 220 mm shaft was analyzed and the spiral groove geometries optimized for good forward rotational stiffness at design pressure and speed, and acceptable reverse rotation capability at lower speed levels. The parameters for optimization include number of grooves, groove angle, groove depth and land-to-groove width ratio. The optimized spiral groove design was machined into smaller prototype hardware and tested in a test cell. Test conditions were modified to simulate an actual groove operating environment. A computerized real-time data acqusition system was utilized to record speed, pressure, temperature, leakage, and vibration readings. The seals were operated in both directions, forward and reverse, and cycled to insure reliability. These seals showed good operating characteristics in forward rotation even with high vibration levels. At significant pressure levels, the optimized spiral groove configuration is a robust design in both directions of rotation. At reduced pressure levels the reverse rotation testing evidenced slight face contact but the temperature levels and amount of wear were acceptable. The seal performance is directly related to the pressure, speed, and time of reverse rotation.

Analysis of Spiral-Groove Face Seals for Liquid Oxygen

Analyses and predicted performance of a 50-mm diameter, spiral-groove face seal to seal liquid oxygen at 5.17 MPa pressure, and operating at surface speed of 183 mls are described. The pressure-balanced spiral-groove concept is introduced that circulates spiral-groove flow independent of leakage flow. Independent flow paths preclude overheating from vaporization and consequent flow blockage. The analysis accounts for fluid turbulence and inertia, thermoelastic distortions, and dynamic response. An operating-range map was developed as a function of speed and pressure. The fluid-film analysis is summarized in the Appendix.

Analytical Investigation of the Spiral Groove Face Seal

An analytical investigation of both a simplified and a comprehensive mathematical model of a spiral groove face seal, using the “narrow seal” approximation. The sealing fluid is assumed to be incompressible and Newtonian. The inertial effects associated with seal curvature are incorporated in the comprehensive model. The results of the analysis are programmed for computer computation in order to facilitate their application in parametric design studies. Performance characteristics are calculated for some particular seal designs.

Spiral Groove Face Seal Concepts; Comparison to Conventional Face Contact Seals in Sealing Liquid Sodium (400 to 1000 Deg F)

Conventional face contact seal performance was improved by incorporation of the spiral-groove geometry. Both conventional face contact seals and seals with spiral grooves were used to seal liquid sodium at a pressure of 20 lb per sq in. gage (14.0 N/cm2 gage), and a sliding velocity of 79 fps (24 m/sec). In comparison with conventional face contact seals, seals with spiral grooves had negligible leakage. The wear and contact patterns indicated that the spiral-groove seal operated with separation of the sealing surfaces, which is necessary for long life. Supporting studies (sealing oil) on face contact seals employing the spiral-geometry are discussed. Successful low-leakage operation was not achieved with conventional face contact seals having carbide seal seats and nosepieces (hard on hard). Thermal and pressure distortions caused edge contact, wear, and scoring. Conventional face contact seals having seal seats and nosepieces with wear-in properties (soft on hard) showed more leakage than those with carbide sealing surfaces.