Experimental Analysis of Floating Ring Annular Seals and Comparisons With Theoretical Predictions

2015 ◽  
Author(s):  
Antoine Mariot ◽  
Mihai Arghir ◽  
Pierre Hélies ◽  
Jérôme Dehouve
Keyword(s):  
Theoretical Model ◽  
High Speed ◽  
Equations Of Motion ◽  
Operating Conditions ◽  
Radial Clearance ◽  
Maximum Pressure ◽  
Friction Forces ◽  
Carbon Ring ◽  
Annular Seal ◽  
Annular Seals

Floating ring annular seals represent one of the solutions for controlling leakage in high speed rotating machinery. They are generally made of a carbon ring mounted in a steel ring for preserving their integrity. Low leakage is ensured by the small clearance of the annular space between the carbon ring and the rotor. Under normal operating conditions, the ring must be able to “float” on the rotor in order to accommodate its vibration. Impacts between the carbon ring and the rotor may occur when the annular seal is locked up against the stator and the amplitude of rotor vibrations are larger than the radial clearance. This situation is prohibited because it rapidly leads to the destruction of the carbon ring. The present work presents experimental results obtained for floating ring annular seals of 38 mm, tandem mounted in a buffer seal arrangement. The rotation speed was comprised between 50 Hz and 350 Hz and maximum pressure drop was 7 bar. For these operating conditions the floating ring follows the rotor vibrations without any impacts. Comparisons were made with a theoretical model based on the equations of motion of the floating ring driven by mass inertia forces, hydrostatic forces in the (main) annular seal and by friction forces on its radial face (also named the “nose” of the seal). The friction coefficient on the nose of the floating ring was estimated from Greenwood and Williamson’s model for mixed lubrication. The present analysis validates the theoretical model used for predicting the dynamic response of the floating ring for a given rotor motion.

Experimental Analysis of Floating Ring Annular Seals and Comparisons With Theoretical Predictions

2015 ◽  
Vol 138 (4) ◽  
Author(s):  
Antoine Mariot ◽  
Mihai Arghir ◽  
Pierre Hélies ◽  
Jérôme Dehouve
Keyword(s):  
Theoretical Model ◽  
High Speed ◽  
Equations Of Motion ◽  
Operating Conditions ◽  
Radial Clearance ◽  
Maximum Pressure ◽  
Friction Forces ◽  
Carbon Ring ◽  
Annular Seal ◽  
Annular Seals

Floating ring annular seals represent one of the solutions for controlling leakage in high-speed rotating machinery. They are generally made of a carbon ring mounted in a steel ring for preserving their integrity. Low leakage is ensured by the small clearance of the annular space between the carbon ring and the rotor. Under normal operating conditions, the ring must be able to “float” on the rotor in order to accommodate its vibration. Impacts between the carbon ring and the rotor may occur when the annular seal is locked up against the stator and the amplitude of rotor vibrations are larger than the radial clearance. This situation is prohibited because it rapidly leads to the destruction of the carbon ring. The present work presents experimental results obtained for floating ring annular seals of 38 mm, tandem mounted in a buffer seal arrangement. The rotation speed was comprised of between 50 Hz and 350 Hz, and maximum pressure drop was 7 bar. For these operating conditions, the floating ring follows the rotor vibrations without any impacts. Comparisons were made with a theoretical model based on the equations of motion of the floating ring driven by mass inertia forces, hydrostatic forces in the (main) annular seal, and by friction forces on its radial face (also named the “nose” of the seal). The friction coefficient on the nose of the floating ring was estimated from Greenwood and Williamson's model for mixed lubrication. The present analysis validates the theoretical model used for predicting the dynamic response of the floating ring for a given rotor motion.

Analytic Modeling of Floating Ring Annular Seals

2012 ◽  
Vol 134 (5) ◽  
Author(s):  
Mihai Arghir ◽  
Manh-Hung Nguyen ◽  
David Tonon ◽  
Jérôme Dehouve
Keyword(s):  
Working Conditions ◽  
Pressure Field ◽  
Hydrodynamic Pressure ◽  
Radial Clearance ◽  
Inertia Force ◽  
Friction Forces ◽  
Leakage Flow Rate ◽  
Annular Seal ◽  
Inertia Forces ◽  
Annular Seals

In order to avoid contact between the vibrating rotor and the stator, annular seals are designed with a relatively large radial clearance (∼100 μm) and, therefore, have an important leakage. The floating ring annular seal is able to reduce the leakage flow rate by using a much lower clearance. The seal is designed as a ring floating on the rotor in order to accommodate its vibrations. The pressure difference between the upstream and the downstream chambers is pressing the nose of the floating ring (secondary seal) against the stator. The forces acting on the floating ring are the resultant of the hydrodynamic pressure field inside the primary seal, the friction forces in the secondary seal, and the inertia forces resulting from the non-negligible mass of the ring. For proper working conditions, the ring of the annular seal must be able to follow the vibration of the rotor without any damage. Under the effect of the unsteady hydrodynamic pressure field (engendered by the vibration of the rotor), of the friction force, and of the inertia force, the ring will describe a periodic, a quasi-periodic, or a chaotic motion. Damage can come from heating due to friction in the secondary seal or from repeated impacts between the rotor and the ring. The present work presents an analytic model able to take into account only the synchronous periodic whirl motion of the floating ring.

Analytic Modelling of Floating Ring Annular Seals

2011 ◽  
Author(s):  
Mihai Arghir ◽  
Manh-Hung Nguyen ◽  
David Tonon ◽  
Je´roˆme Dehouve
Keyword(s):  
Working Conditions ◽  
Pressure Field ◽  
Hydrodynamic Pressure ◽  
Radial Clearance ◽  
Inertia Force ◽  
Friction Forces ◽  
Leakage Flow Rate ◽  
Annular Seal ◽  
Inertia Forces ◽  
Annular Seals

In order to avoid contact between the vibrating rotor and the stator annular seals are designed with a relatively large radial clearance (∼100 μm) and therefore have an important leakage. The floating ring annular seal is able to reduce the leakage flow rate by using a much lower clearance. The seal is designed as a ring floating on the rotor in order to accommodate its vibrations. The pressure difference between the upstream and the downstream chambers is pressing the nose of the floating ring (secondary seal) against the stator. The forces acting on the floating ring are the resultant of the hydrodynamic pressure field inside the primary seal, the friction forces in the secondary seal and the inertia forces resulting from non-negligible mass of the ring. For proper working conditions the ring of the annular seal must be able to follow the vibration of the rotor without any damage. Under the effect of the unsteady hydrodynamic pressure field (engendered by the vibration of the rotor), of the friction force and of the inertia force, the ring will describe a periodic, a quasi-periodic or a chaotic motion. Damage can come from heating due to friction in the secondary seal or from repeated impacts between the rotor and the ring. The present work presents an analytic model able to take into account only the synchronous periodic whirl motion of the floating ring.

Influence of geometric parameters and operating conditions on the thermohydrodynamic behaviour of plain journal bearings

2000 ◽  
Vol 214 (5) ◽  
pp. 445-457 ◽  
Author(s):  
I Pierre ◽  
M Fillon
Keyword(s):  
High Speed ◽  
Journal Bearing ◽  
Three Dimensional ◽  
Journal Bearings ◽  
Operating Conditions ◽  
Thermal Dissipation ◽  
Radial Clearance ◽  
Geometric Factors ◽  
Essential Components ◽  
Mass Flowrate

Hydrodynamic journal bearings are essential components of high-speed machinery. In severe operating conditions, the thermal dissipation is not a negligible phenomenon. Therefore, a three-dimensional thermohydrodynamic (THD) analysis has been developed that includes lubricant rupture and re-formation phenomena by conserving the mass flowrate. Then, the predictions obtained with the proposed numerical model are validated by comparison with the measurements reported in the literature. The effects of various geometric factors (length, diameter and radial clearance) and operating conditions (rotational speed, applied load and lubricant) on the journal bearing behaviour are analysed and discussed in order to inform bearing designers. Thus, it can be predicted that the bearing performance obtained highly depends on operating conditions and geometric configuration.

Application of computational fluid dynamics for thermohydrodynamic analysis of high-speed squeeze-film dampers

2019 ◽  
Vol 43 (3) ◽  
pp. 306-321 ◽  
Author(s):  
Maxime Perreault ◽  
Sina Hamzehlouia ◽  
Kamran Behdinan
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
High Speed ◽  
Operating Conditions ◽  
Squeeze Film ◽  
Radial Clearance ◽  
Base Line ◽  
Squeeze Film Dampers ◽  
Shaft Deflection ◽  
Whirl Speed

In high-speed turbomachinery, the presence of rotor vibrations, which produce undesirable noise or shaft deflection and losses in performance, has brought up the need for the application of a proper mechanism to attenuate the vibration amplitudes. Squeeze-film dampers (SFDs) are a widely employed solution to the steady-state vibrations in high-speed turbomachinery. SFDs contain a thin film of lubricant that is susceptible to changes in temperature. For this reason, the analysis of thermohydrodynamic (THD) effects on the SFD damping properties is essential. This paper develops a computational fluid dynamics (CFD) model to analyze the THD effects in SFDs, and enabling the application of CFD analysis to be a base-line for validating the accuracy of analytical THD SFD models. Specifically, the CFD results are compared against numerical simulations at different operating conditions, including eccentricity ratios and journal whirl speeds. The comparisons demonstrate the effective application of CFD for THD analysis of SFDs. Additionally, the effect of the lubricant THDs on the viscosity, maximum and mass-averaged temperature, as well as heat generation rates inside the SFD lubricant are analyzed. The temperature of the lubricant is seen to rise with increasing whirl speed, eccentricity ratios, damper radial clearance, and shaft radii.

An Analysis of Power Characteristics of Oil-Free Scroll Vacuum Pumps

2020 ◽  
pp. 37-43
Author(s):  
A.V. Tyurin ◽  
A.V. Burmistrov ◽  
A.A. Raykov ◽  
S.I. Salikeev
Keyword(s):  
Mathematical Model ◽  
Power Efficiency ◽  
High Speed ◽  
Pressure Sensors ◽  
Operating Conditions ◽  
Total Power ◽  
Radial Clearance ◽  
Geometrical Parameters ◽  
Power Characteristics ◽  
Indicator Power

This paper presents an analysis of the indicator power of an oil-free scroll vacuum pump based on the indicator diagrams obtained through high-speed pressure sensors. These values are compared with the results of calculations using a mathematical model of the pump working process. It is shown that the divergence of the calculated results and experimental values does not exceed 4%, which confirms the adequacy of the developed mathematical model. The total power of the scroll pump exceeds the indicator power by more than 2 times due to the friction losses between the face seals and disks of the reciprocal scroll elements, friction losses in the stuffing box seals and rolling bearings, as well as due to the coefficient of efficiency of the motor. The influence of the radial clearance between the scroll elements on the power consumption is considered. It is shown that at low pressures nearing the ultimate pressure, the power increases with the increased clearance, while at inlet pressures exceeding 40 kPa it decreases. The performed analysis can be used for selecting the optimal geometrical parameters of the scroll elements and increasing power efficiency of the pump depending on specific operating conditions.

Eccentricity Effects on the Rotordynamic Coefficients of Plain Annular Seals: Theory Versus Experiment

1997 ◽  
Vol 119 (3) ◽  
pp. 443-447 ◽  
Author(s):  
O. R. Marquette ◽  
D. W. Childs ◽  
L. San Andres
Keyword(s):  
High Speed ◽  
Small Motion ◽  
Rotordynamic Coefficients ◽  
Annular Seal ◽  
Theory Versus ◽  
High Speed Data ◽  
Static Eccentricity ◽  
Good Signal ◽  
Good Agreement ◽  
Annular Seals

Reliable high-speed data are presented for leakage and rotordynamic coefficients of a plain annular seal at centered and eccentric positions. A seal with L/D = 0.45 was tested, and measured results have good signal-to-noise ratios. The influence on rotordynamic coefficients of pressure drop, running speed, and static eccentricity was investigated. There is an excellent agreement between experimental and theoretical results in the centered position, even for direct inertia terms, which have not shown good agreement with predictions in past studies. However, the rotordynamic coefficients are more sensitive to changes in eccentricity than predicted. These results suggest that, in some cases, annular seals for pumps may need to be treated more like hydrodynamic bearings, with rotordynamic coefficients which are valid for small motion about a static equilibrium position versus the present eccentricity-independent coefficients.

Jumping Phenomenon in Journal Bearing

1991 ◽  
Author(s):  
Krystof Kryniski
Keyword(s):  
High Speed ◽  
Standard Procedure ◽  
Journal Bearings ◽  
Operating Conditions ◽  
Theory And Practice ◽  
Fluid Film ◽  
Design Parameters ◽  
Radial Clearance ◽  
Rotor Systems ◽  
Rotating Machine

Abstract Due to their reliability and low maintenance costs over an extended service time, the journal bearings, also known as fluid-film bearings, are commonly incorporated in the super-critical rotor systems. Together with proven balancing methods, they allow rotating machine to pass smoothly through the various of critical speeds, both during start-ups and shut-downs. However, journal bearings need to be designed very carefully, as at some operating conditions (speed and load), they may introduce the undesired effects, such as unstable operations or sub-harmonic resonances. The standard procedure leading to the optimum fluid-film bearing design is based on the bearing capacity, defined by the Sommerfield number [1][2]. When Sommerfield number is determined, all design parameters, such as viscosity, radial clearance, diameter and rotation speed, etc. are matched to satisfy the engineering requirements specified. The procedure is considered to be completely reliable and is commonly used in turbo-machinery and high-speed compressor design. However, the significant divergences between theory and practice were observed with the increase of a bearing radial clearance [3].

Analysis of the Radial-Axial Oscillations of the Rotor of a High-Speed Pump

2014 ◽  
Vol 630 ◽  
pp. 341-349 ◽  
Author(s):  
Volodymyr Martsynkovskyy ◽  
Oleksii Zhulov ◽  
Czeslaw Kundera
Keyword(s):  
Axial Force ◽  
High Speed ◽  
Hydrodynamic Forces ◽  
Frequency Characteristics ◽  
Radial Clearance ◽  
Annular Seals

The joint radial-axial oscilations of onemass model of rotor of high-speed pump are considered taking into account hydrodynamic forces, arising up in the radial clearance of annular seals. Connection of axial oscilations with radial is conditioned by dependence of conductivity of annular throttle, consequently, and axial force of balancing device, from the excentricity of shaft in the annular collar. amplitude and phase frequency characteristics of the forced oscilations, excited by harmonically changing pressure and static unbalance.

scholarly journals Experimental Rotordynamic Characterization of Annular Seals: Facility and Methodology

1998 ◽  
Author(s):  
J. Mark Darden ◽  
Eric M. Earhart ◽  
George T. Flowers
Keyword(s):  
High Speed ◽  
Quality Data ◽  
Test Rig ◽  
Stability Margins ◽  
Rotordynamic Coefficients ◽  
Annular Seal ◽  
Theoretical Predictions ◽  
High Reynolds ◽  
Annular Seals

Annular seals are known to enhance rotordynamic stability margins and minimize vibration response levels in high-speed rotating machinery. Theoretical predictions for the rotordynamic characteristics of annular seals exist but additional experimental data is needed to properly anchor these results. NASA’s Marshall Space Flight Center (MSFC) has developed an annular seal test rig and facility to experimentally characterize axially-fed annular seals. The objective of MSFC’s annular seal test rig is to obtain the rotordynamic coefficients (direct and cross-coupled stiffness, damping, and added mass) for a variety of high Reynolds number annular seals. The MSFC test rig supports centered-seal testing with inlet pressures up to 138 bars (2000 psi) and flow rates of over 946 liters per minute (250 gpm). The rig’s shaft is powered by a 186 kilowatt (250 horsepower) steam turbine capable of rotational speeds of over 20,000 revolutions per minute (rpm). A description of the identification process used to obtain rotordynamic coefficients is given as well as procedures for ensuring quality data. Experimental results for a smooth annular seal with an L/D = 0.5 is presented. Excellent agreement between experimental and theoretical results is obtained.

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