Non-contacting Seals Research Articles

Numerical solution of a flow inside a labyrinth seal

The aim of this study is a behaviour of a flow inside a labyrinth seal on a rotating shaft. The labyrinth seal is a type of a non-contact seal where a leakage of a fluid is prevented by a rather complicated path, which the fluid has to overcome. In the presented case the sealed medium is the air and the seal is made by a system of 20 teeth on a rotating shaft situated against a smooth static surface. Centrifugal forces present due to the rotation of the shaft create vortices in each chamber and thus dissipate the axial velocity of the escaping air.The structure of the flow field inside the seal is studied through the use of numerical methods. Three-dimensional solution of the Navier-Stokes equations for turbulent flow is very time consuming. In order to reduce the computational time we can simplify our problem and solve it as an axisymmetric problem in a two-dimensional meridian plane. For this case we use a transformation of the Navier-Stokes equations and of the standard k-omega turbulence model into a cylindrical coordinate system. A finite volume method is used for the solution of the resulting problem. A one-side modification of the Riemann problem for boundary conditions is used at the inlet and at the outlet of the axisymmetric channel. The total pressure and total density (temperature) are to be used preferably at the inlet whereas the static pressure is used at the outlet for the compatibility. This idea yields physically relevant boundary conditions. The important characteristics such as a mass flow rate and a power loss, depending on a pressure ratio (1.1 - 4) and an angular velocity (1000 - 15000 rpm) are evaluated.

Diagnosis of the Phenomenon of Flow as an Inspiration to Inventions in the Domain of Constructing Hydraulic Machines

Analytical and empirical investigations concerning the flow through clearances of non-contacting seals indicate the occurrence of interactions between the walls of the ducts [1]. Investigations of flows in the transverse clearance between annular front of surfaces have show that in the case of a convergence of the clearing the pressure field is asymmetrical. In the case of a forced centrifugal flow, the moment caused by the pressure forces in the transvers clearance opposes the contact of the surfaces of its walls. At centripetal flow the case has opposite effect. The results of calculations of the pressure field concerning a laminar centrifugal flow through the face clearance have been presented. Laboratory tests of such a centrifugal flow have been quoted in [2]. The effects of the pressure fields in the clearances of non-contacting seals, opposing contacts between the walls constituting longitudinal eccentric or transverse converging clearances, were utilized in patented inventions [3–8]. The inventions [3,4] have been dealt with by the authors of [1]. The presented paper describes the structural solutions concerning the inventions [5,6, 7 and 8].

Contact-free exhaust system for vacuum compatible gas bearing guides

Abstract Using linear gas bearing guides in a high vacuum environment, the common method to keep the vacuum quality is to exhaust the gas emitted by the bearing pads before leaking into the vacuum chamber. Thereby the exhaust tubes between the guide and the exhaust pumps should interfere with the guide as little as possible while maintaining a flexible connection and a highly effective exhaustion rate. A novel exhaust system that implements these requirements is described within this paper. The major achievement was the realization of two exhaust tubes slidable into one another combined with the known method of non-contact clearance seals, thus enabling an highly efficient and yet disturbance free exhaustion. This setup was developed and characterized at static and dynamic conditions. An analytical model for dimensioning the non-contact seal was worked out and experimentally verified. The number of seal stages and the clearance height were identified as the major impact factors on the leakage rate of the setup. It is concluded that the investigated approach is very suitable for vacuum compatible gas bearing guides since a vacuum level in the order of 10 −4 Pa was maintained during the experiments.

A Method of Dual Number for the Aerodynamic Property Analysis of Gas-Lubricated Mechanism：Self-Pressurizing Thrust Bearings and Non-Contacting Face Seals

By using dual number, the dynamic property of gas-lubricated thrust bearings or non-contacting face seals is analyzed in the small perturbation approximation, then an essential conclude, that the perturbation dynamic Reynolds’ equations independently of its whirl frequency, is advanced. According to this, the calculation of the stiffness and damping coefficients independently of system motion equations of bearings and seals is expedited.

Development and Application of Non-Contact Seal Assembly for High-Speed Shaft Ends

Non-contact seal assembly for high-speed shaft ends is introduced. Fluid dynamic calculations and analyses have been made with FLUENT Software on the flowing in the front sealed cavity, the mid labyrinth-sealed cavity and the outside windshield cavity of the seal assembly. The results through the tests are in conformity with those in simulation analyses.

A New Method to Realize Unsteady Calculation of Flow in Labyrinth Seals

As non-contact seal, labyrinth seal is widely used in rotor system of high speed. However, with the development of turbo-machinery toward high performance and huge capacity, gas excitation vibration within the labyrinth seal becomes the main reason threatening safe operating of machinery sets. Recently three dimensional computational fluid dynamic was applied to analyse inside flow in labyrinth seal. These researches, while greatly improve rotordynamic prediction of labyrinth seals, are mostly focused in steady calculation. In fact, rotor inside the seal is whirling in a nonlinear behaviour, which makes the flow unstable. In an effort to analyse the non-linear behaviour of flow in labyrinth seal, this paper utilizes an improved dynamic mesh technology to realize unsteady calculation. The Reynolds Averaged Navier Stokes equations is solved by a commercial CFD program, FLUENT. Steady calculations are firstly done to determine mesh density and turbulence model, then an unsteady analysis is used to study gas excitation force. The influence of initial condition to the unsteady analysis is discussed. This method allows modeling of rotor orbit around the eccentric position and gives prediction of nolinear gas excitation force.

Numerical Analysis of a Spiral-groove Dry-gas Seal Considering Micro-scale Effects

A dry-gas seal system is a non-contact seal technology that is widely used in different industrial applications.Spiral-groove dry-gas seal utilizes fluid dynamic pressure effects to realize the seal and lubrication processes,while forming a high pressure gas film between two sealing faces due to the deceleration of the gas pumped in or out.There is little research into the effects and the influence on seal performance,if the grooves and the gas film are at the micro-scale.This paper investigates the micro-scale effects on spiral-groove dry-gas seal performance in a numerical solution of a corrected Reynolds equation.The Reynolds equation is discretized by means of the finite difference method with the second order scheme and solved by the successive-over-relaxation(SOR) iterative method.The Knudsen number of the flow in the sealing gas film is changed from 0.005 to 0.120 with a variation of film depth and sealing pressure.The numerical results show that the average pressure in the gas film and the sealed gas leakage increase due to micro-scale effects.The open force is enlarged,while the gas film stiffness is significantly decreased due to micro-scale effects.The friction torque and power consumption remain constant,even in low sealing pressure and spin speed conditions.In this paper,the seal performance at different rotor face spin speeds is also described.The proposed research clarifies the micro-scale effects in a spiral-groove dry-gas seal and their influence on seal performance,which is expected to be useful for the improvement of the design of dry-gas seal systems operating in the slip flow regime.

An analytical approach of the thermoelastohydrodynamic behaviour of mechanical face seals operating in mixed lubrication

This article presents a semianalytical analysis of mechanical face seals. The model takes an account of thermal effects and face distortions that are the principal determinants of the performance of mechanical seals. Since the fluid film thickness observed during the operation of mechanical face seals is generally a fraction of a micrometre, asperity contact is also considered. A closed-form solution for the elastic rough surfaces’ contact is obtained by assuming a simplified distribution for asperity height. It has been shown in a previous article that the behaviour of a non-contacting seal is a function of just two dimensionless parameters: the sealing number Se, which depends on the operating and design parameters of the seal, and the coning number Co, which is the ratio between elastic and thermal distortions. When contact involving asperities is considered, the number of dimensionless parameters rises to six. The behaviour of the seal is, in addition, a function of the ratio of the asperity height to the thermal distortion magnitude, the ratio of the elastic properties of the asperities to the sealed fluid pressure, the ratio between dry and viscous frictions, as well as the balance ratio. Nevertheless, this model allows one to determine in a simple and rapid way the performance of a mechanical seal: temperature of the faces, film thickness, leakage, dissipated power, proportion of contact, etc. The model is applied to several examples in order to illustrate the behaviour of a mechanical seal.

密封液自己循環形ビスコシールの特性 : 密封性能およびガス吹き抜け抑止性能(流体工学,流体機械)

The sealing performance and the deterrence performance of gas blowout of a sealant self-circulated viscoseal, which is a kind of noncontact seal, are described. Most of the experimentally determined sealing performances are inferior to the theoretical sealing performances, because eccentricity of the circumferential pressure occurs when the viscoseals are horizontal. First, the circumferential and axial pressure distributions are simulated under the assumption that the resultant force generated in sealant is based on not only the pressurized force but also gravity and the centrifugal force. The corrected sealing performance, which is simulated by taking into account the resultant force based on the above named forces are in good agreement with the experimental results. Second, both the gas-liquid interface and the ingested gas motion are seen by observation of naked eye and flow visualization. The regime diagrams of flow in sealant are ensured. Also, it is confirmed that a small amount of self-circulated sealant causes sufficient deterrence of gas blowout in spite of both a high number of screw shaft revolutions and a high cover gas pressure.

On application of the theory of face seals with microgrooves to high-speed FV engine rotors

With allowance made for thermoelasticity of working surfaces and inertia forces on the lubricant coat, a hydrodynamic problem is solved for the noncontacting face seals with microgrooves in the high-speed rotors of FV engines. Also shown are the initiation of surface waviness in the zone of lubricant coat fracture and the influence of its amplitude upon the seal characteristics.

Non-contact labyrinth seal assembly

Non-contact labyrinth seal assembly

Non-contacting seal uses gas lubrication at high temperature

John Crane has announced the introduction of the Type 2874NE, a new gas lubricated, API 682/ISO 21049 qualified, high temperature non-contacting mechanical seal.

Non-contacting seal for rotating surfaces

Non-contacting seal for rotating surfaces

A Simple Approach to the ThermoElastoHydroDynamic Behavior of Mechanical Face Seals

This article presents a semi-analytical analysis of non-contacting mechanical face seals. The model takes account of thermal effects and face distortions that generally determine the performance of mechanical seals. It is shown that the seal behavior is a function of just two dimensionless parameters: (a) the sealing number Se, which depends on the operating and design parameters of the seal, and (b) the coning number Co, which is the ratio of elastic and thermal distortions. The theoretical results are compared to measurements obtained on an inner pressurized seal. Good agreement on the temperature of the faces and on dissipated power is obtained for various rotation speeds, validating the assumptions used in developing the model. The analysis of the influence of Se and Co on the behavior of mechanical face seals makes it possible to highlight several operating modes.

547 オリフィスによりプレスワールを与える流体力の解析

Non-contacting seal is used to prevent leakage flow for turbomachineries, such as gas turbines and compressors. Since these turbomachineries tend to be operated under high pressure and power, the fluid forces induced at the seal is one of the causes of instability. One way to reduce this instability is to use inlet swirl injection against rotation. In this research, we found the distribution of circumferential velocity and pressure at the inlet of the seal and the effect of injection of inlet swirl on the static and dynamic characteristics.

Measurements of Leakage and Power Loss in a Hybrid Brush Seal

Simplicity, low cost, and easy replacement make labyrinth seals the primary seal type in gas turbines. However, excessive leakage and potential for rotordynamic instability are well known issues. Brush seals effectively control leakage in air breathing engines, albeit only applied for relatively low pressure differentials. Hybrid brush seals (HBSs) are an alternative to resolve poor reliability resulting from bristle tip wear while also allowing for reverse rotation operation. The novel configuration incorporates pads contacting the shaft, which under rotor spinning lifts off due to the generation of a hydrodynamic pressure. The ensuing gas film prevents intermittent contact, thus lowering the operating temperature and thermal distortions and even eliminating bristle wear. The hybrid brush seal improves sealing, is more durable and reliable than conventional brush seals, and allows reverse shaft rotation without seal damage. This paper presents measurements of power loss and leakage in a HBS for increasing pressure differentials over a range of rotor speeds. The test HBS, Haynes-25 bristle pack (∼850 bristles∕cm) and 45 deg lay angle, is 166.4 mm in diameter and integrates 20-arcuate pads connected with thin electrical-discharge machined webs (EDM-webs) to the seal casing. The webs are designed with low radial stiffness to allow for rotor excursions and high axial stiffness to avoid pad pitching motions resulting from high pressure differentials across the seal. Measured drag power at low rotor speeds (<11 m∕s at 1300 rpm) decreases as the pressure differential across the seal increases. At a fixed rotor speed, a significant drop in drag torque (and drag power) ensues as the supply pressure increases, thus demonstrating that a gas film separates the rotor from the seal pads. Additionally, the operating temperature measured at the rotor/seal interface remains approximately constant (∼24°C) during tests with shaft rotation (power loss and drag torque measurements) under pressurized conditions, indicating that the rotor and seal pads are not in contact. Flow rate measurements at room temperature (25°C) show an improved sealing ability with a leakage reduction of about 36% when compared with a first generation shoed-brush seal. The HBS calculated effective clearance (∼50 μm) is approximately 70% smaller than the radial clearance (∼180 μm) of an ideal noncontacting seal with similar rotor diameter. Improved brush seal technology will increase the efficiency of gas turbines while also aiding to improve the engine stability and to reduce vibrations.

고추력 액체 로켓 엔진용 터보펌프의 회전체동역학 해석

볼 베어링과 펌프 비접촉 실의 동특성을 고려하여 고추력 액체 로켓 엔진용 터보펌프의 회전체동역학 해석이 수행되었다. 회전 고유진동수와 감쇠비를 예측하기 위하여 회전속도에 따른 복소 고유치 해석이 수행되었다. 동기 회전체 질량 불평형 응답과 시간 과도 응답 해석을 통하여 회전체의 임계속도와 불안정 운전 시작 속도가 확인되었다. 수치 해석 결과로부터 후방 베어링 강성이 임계속도와 불안정성 예측에 있어서 가장 중요한 인자로 확인되었는데, 이는 1차 모드가 터빈부 회전축 굽힘 모드인 것에 기인한다. 임계속도에 있어서 펌프 실의 영향은 후방 베어링 강성이 감소할수록 그리고 전방 베어링 강성이 증가할수록 확대되는 것으로 나타났다. A rotordynamic analysis is performed for a high thrust class liquid rocket engine turbopump considering the dynamic characteristics of ball bearings and pump noncontact seals. Complex eigenvalue problems are solved to predict the rotating natural frequencies and damping ratios as a function of rotating speeds. Synchronous rotor mass unbalance response and time transient response analyses are also performed to figure out the rotor critical speed and the onset speed of instability. From the numerical analysis, it is found that the rear bearing stiffness is most important parameter for the critical speed and instability because the 1st mode is turbine side shaft bending mode. The pump seal effect on the critical speed is enlarged as the rear bearing stiffness decreases and the front bearing stiffness increases.

Pressure Drop Characteristics of Water Flow Through Static Annular and Triangular Cavity Labyrinth Seals

Non-contacting static seals are intended to provide high pressure drop at different leakage flow rates for better sealing. In special applications such as cryogenic engines and nuclear reactors which have high sealing requirements, conventional annular seals and circular-grooved square cavity labyrinth seals often do not meet the demand. This paper investigates newer configurations like circular-grooved triangular cavity labyrinth seals and sinusoidal-grooved triangular cavity labyrinth seals which can provide improved sealing than conventional seals. For these seals, pressure drop data over a wide range of water flow rates has been obtained using computational simulations and experiments. The pressure drops for the triangular seals are observed to be marginally more than those for square labyrinth seals and markedly higher than those for annular seals. The numerical results are also in good agreement with experimental and available analytical results. In order to highlight the effects of cavity shape and seal configuration, optimisation of a circular-grooved triangular labyrinth seal has been carried out using Artificial Neural Network (ANN), in association with a semi-theoretical model. The pressure drop for the identified optimal triangular labyrinth seal is 16% higher than that of the optimal square labyrinth seal. Among the seals tested, the sinusoidal-grooved triangular labyrinth seal exhibits the highest pressure drop, exceeding that of the optimal circular-grooved triangular labyrinth seal by 57%, at the rated flow rate.

909 しゅう動面に凹凸を有する非接触シールの力学的特性 : 集中格子を用いた数値解析(OS11-2 機械等の動的解析,オーガナイズドセッション:11 機械と車輌のダイナミクス)

909 しゅう動面に凹凸を有する非接触シールの力学的特性 : 集中格子を用いた数値解析(OS11-2 機械等の動的解析,オーガナイズドセッション:11 機械と車輌のダイナミクス)

Development of Step-and-Scan-Type XY-Stage System for Electron Beam Systems

The trend towards minimization in ultralarge-scale integration (ULSI) fabrication requires an increasingly precise motion accuracy for an XY-stage in a high-vacuum environment of electron beam (e-beam) systems. Aerostatic bearings allow for an extremely smooth motion, because the slider of the XY-stage is supported by an air film under a noncontact condition. However, such an XY-stage in aerostatic bearings is not easily introduced into the e-beam systems because of the markedly high amount of exhaust gas leaking into a vacuum chamber. In this paper, we describe a newly developed hybrid XY-stage guided by aerostatic bearings equipped with a noncontact seal mechanism for scanning motion and by mechanical rolling guides for stepping motion.