Gas Face Seal Research Articles

Evolution of bi-Gaussian surface parameters and sealing performance for a gas face seal under a low-speed condition

Abstract A spiral groove gas face seal, serving as a typical non-contacting seal, commonly encounters face contact during a low-speed condition such as the startup, shutdown, barring and warming-up operations. By using a discrete manner, the surface-topography evolution of the two mated sealing rings during a low-speed barring process is achieved, and is in a great agreement with the previous standard tests. The bi-Gaussian surface-topography evolution is found to well identify the end running-in, material adhesion and deep scratches. Furthermore, the surface-topography evolution exhibits a high correlation with the recorded seal-performance indexes including leakage rate, torque and acoustic emission signal, which is helpful in exploring the deterioration mechanism of sealing performance.

Numerical analysis of the non-contacting gas face seals

The non-contacting gas face seals are used in high-performance devices where the main requirements are safety and reliability. Compliance with these requirements is made possible by careful research and analysis of physical processes related to, inter alia, fluid flow through the radial gap and ring oscillations susceptible to being housed in the enclosure under the influence of rotor kinematic forces. Elaborating and developing mathematical models describing these phenomena allows for more and more accurate analysis results. The paper presents results of studies on stationary ring oscillations made of different types of materials. The presented results of the research allow to determine which of the materials used causes the greatest amplitude of the vibration of the system fluid film-working rings.

Stability and tracking analysis of gas face seals under low-parameter conditions considering slip flow

Dynamic property of a gas face seal is about an internal ability of the mass-spring-damper system consisting of the nonlinear gas film, the flexible support, and the component mass or moment of inertia to handle ambient disturbances. Stability and tracking properties are important dynamic components, the current research for which mainly focuses on high-speed and high-pressure conditions in turbomachinery applications. In this paper, perturbation theory is used to obtain the linearized properties of the gas film in a spiral groove gas face seal, where the Boltzmann-Reynolds model with Fukui-Kaneko approximation is involved to account for slip flow under low-parameter conditions. Transmissibility of the step jump method is introduced into the perturbation method, and a critical ambient-disturbance amplitude is further proposed to cover the defect of transmissibility in characterizing the tracking property. The effects of slip flow on the stability and tracking properties of gas face seals are explored. The results show that slip flow induces an extra “relaxation region” in the critical transverse moment of inertia, providing a softer demand for angular stability. With regard to transmissibility, slip flow will induce an advantageous effect on transmitting the rotor motion to the stator. However, after considering the space required for tracking motions, the results of critical amplitude indicate that slip flow will induce an extra “rigorous region”, leading gas face seals to require more conservative design and more rigorous manufacture and assembly for non-contacting tracking.

Applicability Analysis of Steady-state Models for Spiral Groove Gas Face Seals

Applicability Analysis of Steady-state Models for Spiral Groove Gas Face Seals

Thermoelastohydrodynamic behaviour of inclined-ellipse dimpled gas face seals

The thermoelastohydrodynamic performance of an inclined-ellipse dimpled gas face seal is analyzed. The pressure distributions of the gas film and temperature fields of the seal rings and gas film are presented considering thermal and elastic distortions. Then, the influences of texturing parameters, including dimple inclination angle and dimple depth, on sealing performance are investigated under different operating parameters such as rotational speeds and seal pressures. The results show that face distortions lead to a decrease in the hydrodynamic effect at high rotational speed. The analysis shows that the opening force can decrease by more than 50% as the rotational speed increases from 0 to 35000 r min−1. The influence of face distortion on the seal performance, such as opening force and leakage characteristic, gradually increases with the rotational speed.

Thermoelastohydrodynamic characteristics of T-grooves gas face seals

Thermoelastohydrodynamic characteristics of T-groove gas face seals are numerically investigated. The film pressure and temperature fields are calculated with consideration of the elastic and thermal distortions of the rings and the choked flow effect. The temperature difference between the outer radius and the inner radius is about 6K below 1.0MPa, and about 60K above 1.0MPa. Analysis results also show that a convergent gap is formed under 1.0MPa and a divergent gap is formed when the sealing pressure is larger than 1.0MPa. The thermoelastohydrodynamic effect becomes obvious and leads to significant decrease of the opening force when the sealing pressure is larger than 1.0MPa. Besides, the dynamic opening force increases with the increasing rotational speed at low sealing pressures, exceeding 2% in degree in the case of sealing 0.5MPa in the analysis, but it decreases at high pressures, exceeding 6% in degree in the case of sealing 3.0MPa. T-groove gas face seal is more suitable to be applied under conditions of low sealing pressure and high rotational speed.

Influence analysis of secondary O-ring seals in dynamic behavior of spiral groove gas face seals

The current research on secondary O-ring seals used in mechanical seals has begun to focus on their dynamic properties. However, detailed analysis of the dynamic properties of O-ring seals in spiral groove gas face seals is lacking. In particular a transient study and a difference analysis of steady-state and transient performance are imperative. In this paper, a case study is performed to gauge the effect of secondary O-ring seals on the dynamic behavior (steady-state performance and transient performance) of face seals. A numerical finite element method (FEM) model is developed for the dynamic analysis of spiral groove gas face seals with a flexibly mounted stator in the axial and angular modes. The rotor tilt angle, static stator tilt angle and O-ring damping are selected to investigate the effect of O-ring seals on face seals during stable running operation. The results show that the angular factor can be ignored to save time in the simulation under small damping or undamped conditions. However, large O-ring damping has an enormous effect on the angular phase difference of mated rings, affecting the steady-state performance of face seals and largely increasing the possibility of face contact that reduces the service life of face seals. A pressure drop fluctuation is carried out to analyze the effect of O-ring seals on the transient performance of face seals. The results show that face seals could remain stable without support stiffness and O-ring damping during normal stable operation but may enter a large-leakage state when confronting instantaneous fluctuations. The oscillation-amplitude shortening effect of O-ring damping on the axial mode is much greater than that on the angular modes and O-ring damping prefers to cater for axial motion at the cost of angular motion. This research proposes a detailed dynamic-property study of O-ring seals in spiral groove gas face seals, to assist in the design of face seals.

Spiral-grooved gas face seal for steam turbine shroud tip leakage reduction: Performance and feasibility analysis

In order to minimize shroud leakage and its effect on aerodynamic loss of steam turbines, a new shroud seal design by employing spiral-grooved gas face seal theory is presented. To verify the method, a flow numerical simulation was conducted to investigate the effect of the new shroud seal on aerodynamic loss in steam turbine rotor row. The results show, compared with a traditional two-tooth labyrinth seal, the new shroud seal leakage is reduced by 99.3%, and the rotor row efficiency is improved by 1.9%. Furthermore, a feasibility analysis including lift and stiffness of gas film, tracking response of primary ring and deformation of mating ring was presented. The present design is a potential approach to further improve turbine stage performance.

Thermo-hydrodynamic characteristics of spiral groove gas face seals operating at low pressure

Thermo-hydrodynamic behaviors of spiral groove gas face seals are investigated for the cases of low seal pressure. Pressure and temperature fields of gas film are calculated, and then influence of thermal distortion on seal performance are analyzed. It is found that spiral grooves lead to complex film temperature distributions and rotational speed results in the increase of whole film temperature. But the shear heat and pumping effect of spiral grooves have little influence on film temperature gradient along the leakage direction. The face thermal distortion, forming divergent clearance along the leakage direction, makes the opening force decrease and the leakage increase. A higher seal pressure and clearance will result in a larger thermal distortion. And the rotational speed may enhance the face thermal distortion further in some low pressure cases.

A parametric and dynamic analysis of non-contacting gas face seals with modified surfaces

The application of various modifications such as micro-channels, compartments, micro-pores, texturing in mechanical non-contacting seals causes changes of dynamic properties of the medium layer. This paper presents the results of analyses pertaining to the impact of surface topography on the vibrations of cooperating rings. The balance of forces working in a seal affects non-contacting operation, i.e. maintaining the stability of the medium layer separating the rings. The consequences thereof include: controlled leak, small wear of sliding surfaces and prolonged lifespan.The presented model of gas face seals includes the non-linear Reynold׳s equation as well as the equations of dynamics describing the vibrations of the stator which were solved simultaneously with the use of numerical methods. The conducted analyses of the modeled seals and the obtained results may be useful when designing and choosing surface topography to the set operating conditions. It results in longer working time and reliable operation of devices in which those seals were installed.

Correlational Research of Bionics Design of Dry Gas Face Seal Groove

Based on statistical method and gas lubrication theory, the correlation mathematical models of outline constructional feature of a bird wing and face groove feature of a dry gas seal(DGS) are established, and the film pressure controlling equation of a DGS is set up. The membership grades and their calculation expressions used to define face groove geometrical feature of a DGS are presented based on fuzzy mathematics, and DGSs are classified according to the membership grades. The gas film pressure control equations are resolved by use of finite difference method, and the gas film stiffness of a DGS is obtained. The correlation between the constructional feature parameters of bird wing outlines and flight speed and the correlation between face groove geometric parameters and operational stability of a DGS at different speeds are comparatively analyzed. Results show that the correlations between the geometric constructional feature parameters of bird wing outlines or face grooves and their flight speeds or operational speeds are in moderate degree. That is to say long wings give a bird stability, and long narrow wings give a bird more stability at high flight speeds, and long grooves give a DGS stability, and long narrow grooves give a DGS more stability at high operational speeds, correspondingly. Results also reveal that the relationship between a bird biological model and a DGS engineering model exists exactly. The feasibility of bionic design of face groove based on the geometric characteristics of bird wing outlines is demonstrated. The important theory basis is provided for the bionic design of a DGS.

Analyses of both steady behavior and dynamic tracking of non-contacting spiral-grooved gas face seals

The analyses for steady and unsteady sealing behaviors of spiral-grooved gas face seals are presented by finite element method. The element with nine nodes and four quadratic cures is used. And for avoiding the film thickness discontinuity over the grooves, two of them coincide with the circular arcs and the others approximate to the spiral lines. In steady-state analysis, the steady-state Reynolds equation is used, and different element meshes are utilized for different sealed pressures. The load capacity and the lubricant leakage on gas face seals are shown for different compressibility numbers and sealed pressures. Thus the optimal sealed pressure and the gas amount needed in actual applications can be determined according to the numerical results. For the dynamic tracking of the stator, the direct-dynamic analysis is used, and the explicit form of the unsteady compressible Reynolds equation is found by weighting the film thickness in each element. The initial pressure profile and the initial closing force are determined at the given sealed pressure. The dislocations due to the external shock disturbances are considered, including the rotor runout only, the stator misalignment only, and the mixed dislocations. The possibility of face contact, the detectable central clearance between stator and rotor, and the leakage under unsteady operation are concerned.

Effect of Surface Roughness on Performance of Spiral Groove Gas Film Face Seal

The three dimensional model was established for studying performance of spiral groove gas face seal. According to machining features of different surface area, the seal face can be divided into three parts, rotor ring grooved area, rotor ring non-grooved area and static ring area. The effect of roughness on seal performance was analyzed based on calculation of three dimensional flow field. The analysis results show that the surface roughness of rotor ring grooved area has great influence on the seal performance, but the influence is little when roughness on non-grooved rotor ring surface and static ring surface. The influence must be considered when surface roughness of rotor ring grooved area bigger than 0.2μm. Roughness of rotor ring surface can increase the loading force while it also can cause the increase of leakage. It is important to select rational roughness when designing gas face seal.

Experimental Investigation of an Inclined Ellipse Dimpled Gas Face Seal

An inclined elliptical dimpled gas face seal was experimentally investigated in order to provide evidence for theoretical study. An experimental setup and theoretical model were developed to study the hydrodynamic effect of this gas seal. Then, opening and steady performance of the seal was measured under different rotational speed and seal pressure. The clearance and leakage rate are discussed for different cases of pressure and rotational speed. The results showed that there was a good correlation between theory and experiment. Both the clearance and the leakage rate increased significantly with increasing rotational speed and seal pressure. The inclined elliptical dimpled gas face seal was a type of hydrodynamic seal.

Pressure dam influence on the performance of gas face seals

The introduction of grooves, micropores, and other forms of surface geometric modifications onto the mating seal plates has been performed to enhance the gas face seal performance. Reducing fluid leakage through the seal surface has been the main motivation for the development of efficient sealing technology for industrial turbomachinery. Pressure dams are generally etched on the seal inner and outer radii to improve even more the seal capability of reducing the gas leakage to atmosphere. This paper presents a finite element analysis carried out to determine the opening force, the flow leakage and the dynamic force coefficients of flat gas face seals with pressure dams operating under stringent conditions. Several curves of steady-state and dynamic seal performance characteristics depict the influence of the pressure dam position and width on the seal performance and efficiency.

Adaptive Control of Mechanical Gas Face Seals With Rotor Runout and Static Stator Misalignment

This paper presents a control methodology that utilizes a robust model reference adaptive control technique to regulate the dynamic behavior of a coned mechanical gas face seal system in a flexibly mounted stator configuration. Individual adaptive controllers are designed for the three stator rigid body degrees of freedom based on the linear portions of their respective equations of motion. The force and moments generated within the gas film are estimated using Kalman filter-based estimators and directly cancelled in the control algorithm using offset control signals. The estimation errors are considered as bounded disturbances to the seal system and are taken into account by the robust adaptive controllers. Simulation results show that the controllers effectively stabilize the stator motion and control the stator tilts to synchronously track the rotor runout with near-zero relative misalignment magnitude and phase shift, thus, minimizing gas leakage.

The Parameters Influencing High-Pressure Mechanical Gas Face Seal Behavior in Static Operation

The increase in the operating pressure of gas compressors makes it necessary to develop numerical tools for designing optimal high-performance mechanical seals. The authors developed a numerical model of the TEHD behavior of an axisymetric mechanical face seal, working with a high-pressure real gas. The model includes thermal and inertia effects and a choked flow condition. Heat transfer between the fluid and the solids as well as elastic and thermal distortions are computed. This article presents a dimensional analysis that allows the influence of inertia effects to be evaluated and a small number of nondimensional parameters determining seal behavior to be identified. A parametric study was carried out to calculate the mechanical face seal performance under various operating conditions. The results are presented as curves for nondimensional load, mass flow, and exit pressure. Temperature versus characteristic nondimensional parameters is also shown.

Real-Time Force and Moment Estimation for Mechanical Gas Face Seal Systems Using Reduced-Order Kalman Filters

A method using reduced-order Kalman filters is developed to estimate the thin gas film axial force and moments in real time for mechanical gas face seal systems in a flexibly mounted stator configuration. First-order Gauss–Markov stochastic models, combined with the stator motion equations, form the basis for the reduced-order Kalman filter estimators. Two schemes are presented to estimate axial force and moments based on stator motion measurements. In one scheme, the force and moments are directly estimated and, in another scheme, a set of proper orthogonal decomposition weighting functions is estimated, from which the gas film force and moments are computed. Both estimators are shown to approximate the gas film axial force and moments successfully for different forcing functions over a wide range of compressibility numbers.

Thermoelastohydrodynamic Behavior of Mechanical Gas Face Seals Operating at High Pressure

A numerical modeling of thermoelastohydrodynamic mechanical face seal behavior is presented. The model is an axisymmetric one and it is confined to high pressure compressible flow. It takes into account the behavior of a real gas and includes thermal and inertia effects, as well as a choked flow condition. In addition, heat transfer between the fluid film and the seal faces is computed, as are the elastic and thermal distortions of the rings. In the first part of this paper, the influence of the coning angle on mechanical face seal characteristics is studied. In the second part, the influence of the solid distortions is analyzed. It is shown that face distortions strongly modify both the gap geometry and the mechanical face seal’s performance. The mechanical distortions lead to a converging gap, while the gas expansion, by cooling the fluid, creates a diverging gap.

Experimental and Numerical Investigation of a Gas Compressor Windback Seal

The effectiveness of a computational fluid dynamics (CFD) commercial code to accurately predict the leakage rate for a windback seal was evaluated. The windback seal under consideration has a rectangular cavity and is similar in design to a gas tooth on stator annular labyrinth seal. The main difference is the windback seal has only one tooth, which continuously winds around the shaft like a screw thread. These seals are used in gas compressors to isolate the gas face seal from bearing oil. A purge gas is passed through the seal into the bearing housing. The helical design allows the seal to clear itself of any oil contamination. The objective is to determine if CFD simulations can be used along with a few experimental tests to study windback seals of this design. Comparison of measurement and predictions for a simple rectangular cavity windback seal shows predictions and measurements comparing very well with maximum differences of 5% for leakage rate. The variation of leakage with shaft speed and pressure ratio across the seal is accurately predicted by the CFD simulations.