Tilting-pad Bearings Research Articles

Study on transient performance of tilting-pad thrust bearings in nuclear pump considering fluid-structure interaction

To study the lubrication performance of tilting-pad thrust bearing (TPTBs) during start-up in nuclear pump, a hydrodynamic lubrication model of TPTBs was established based on the computational fluid dynamics (CFD) method and the fluid-structure interaction (FSI) technique. Further, a mesh motion algorithm for the transient calculation of thrust bearings was developed based on the user defined function (UDF).The result demonstrated that minimum film thickness increases first and then decreases with the rotational speed under start-up condition. The influence of pad tilt on minimum film thickness is greater than that of collar movement at low speed, and the establishment of dynamic pressure mainly depends on pad tilt and minimum film thickness increases. As the increase of rotational speed, the influence of pad tilt was abated, where the influence of the moving of the collar dominated gradually, and minimum film thickness decreases. For TPTBs, the circumferential angle of the pad is always greater than the radial angle. When the rotational speed is constant, the change rate of radial angle is greater than that of circumferential angle with the increase of loading forces. This study can provide reference for improving bearing wear resistance.

Effect of a Reduced Oil Flow Rate on the Static and Dynamic Performance of a Tilting Pad Journal Bearing Running in Both the Flooded and Evacuated Conditions

Abstract The mechanical efficiency of rotating machinery improves as drag power losses in bearings reduce; hence, an operation mode that reduces the supplied flow brings immediate benefits. The paper presents measurements of the static and dynamic load performance conducted with a tilting pad journal bearing configured as flooded and evacuated, and supplied with flow rates from 150% to ∼25% (or lesser) of a nominal magnitude, proportional to shaft speed. The lubricant is ISO VG 46 oil supplied at 60 °C. The four pads bearing has center pivots with single orifice feeds for the flooded condition and spray bar injection for the evacuated condition. The shaft, 102 mm in diameter, operates at two speeds, 6 and 12 krpm (= 64 m/s surface speed), while a static load is applied between pads (LBP). The specific loads equal 345, 1034, and 2068 kPa. A reduction in flowrate makes both bearings operate more eccentrically. The evacuated bearing operates at a larger eccentricity, which for the lowest flowrate does not align with the direction of the applied load, hence displaying a sizable attitude angle. Pad subsurface temperatures are similar for both bearing configurations, although the evacuated bearing is colder by a few degrees Celsius. Drag power losses derived from the oil exit temperatures show the evacuated bearing produces up to ∼40% lesser power loss than the flooded bearing for a nominal oil flowrate. The bearings direct stiffnesses, Kxx and Kyy, increase with applied load and show little dependency on shaft speed. The evacuated bearing has lower magnitude stiffnesses, 20% or so lesser, than the flooded bearing. Damping coefficients, Cxx ∼ Cyy, reduce in magnitude as the flowrate decreases. In particular for low flow rates, 35% or lower, the evacuated bearing shows rather small (though highly uncertain) damping coefficients. For sufficiently small flow rates, operation at 6 krpm shaft speed and under the smallest applied unit load (345 kPa) produced subsynchronous shaft vibrations with a broad band spectrum (subsynchronous shaft vibrations (SSV) hash). The evacuated bearing produced SSV hash at flow rates equal to 30% or so of nominal, while the flooded bearing demanded very low flow rates (∼15% and lesser of nominal) to produce SSV hash. For both bearings, the SSV amplitude motions were rather small in amplitude. The experimental campaign demonstrates that tilting pad bearings (flooded and evacuated) can safely operate with a reduced flowrate (50% or so of nominal) to produce significant savings in drag power losses and without significant effect on the pads' metal temperatures that could affect the bearing long-term operation.

Performance Analysis and Test Verification of Porous Tilting Pad Bearings with Hermetically Sealed Squeeze Film Damper in Parallel

Performance Analysis and Test Verification of Porous Tilting Pad Bearings with Hermetically Sealed Squeeze Film Damper in Parallel

Analysis of flexible air bearing and design of testing machine

The paper takes a type of flexible air bearing as the research object, and the bearing structure is analyzed in detail. Combined with the traditional analysis method of tilting pad bearing and the fluid-solid coupling theory, a new analysis model for performance prediction of the bearing was established. The performance of air bearing with inner diameter of 70mm was calculated by changing the input pressure or the inlet capillary diameter. The structure of the bearing was optimized by analyzing the calculation results, and the structure of the separate inlet nozzle was added. A bearing testing machine is designed for the flexible air bearing test to verify the improvement of bearing performance.

Measuring the fluid film thickness and evaluation of slope parameter to assess the tribological characteristics of tilting pad bearings

Researchers studying lubrication analysis have investigated both mixed and hydrodynamic lubrication. Lubrication analysis has been considered with respect to the slope parameter of the friction surface and surface roughness. Furthermore, the relative slope of the pad bearing surface was confirmed to influence friction characteristics. However, whether the lubrication analysis values are comparable to those obtained via friction tests has remained unclear. In this study, we developed an experimental device to obtain the slope parameter and analyzed the results to experimentally verify the lubrication analysis results. The fluid film thickness was calculated by analyzing the slope parameter obtained from the friction tests, and was used as the input value for the lubrication analysis. Thereafter, the experimental values of the friction coefficient and slope parameter were compared with those obtained via numerical analysis.

Experimental investigation of dynamic behavior of rotor system with a novel double layers flexible support tilting pad bearing

Among all kinds of journal bearings, the tilting pad bearing has the characteristics of high stability. In order to further reduce the vibration and improve the stability of rotor-bearing systems, a novel double layers flexible support tilting pad bearing (DL-FSTPB) is presented in this paper. The bearing utilizes two layers of springs, which have different functions. The offset springs control the swing angle of the tilting pad to ensure the formation of a convergent oil film, and the symmetrical springs are used to change the bearing stiffness coefficient, increase the bearing elasticity, and improve the ability to accommodate misalignment. Experiments were carried out to study the vibration characteristics of the rotor system. The results were analyzed using wavelet analysis of acceleration and displacement, waterfall plots, a wavelet analysis, a run-up process and shaft center orbits areas. The results show that the DL-FSTPB exhibits excellent vibration attenuation characteristics, which can effectively reduce the amplitude and the system vibration level.

Dynamic Coefficients of Tilting Pad Bearing by Perturbing the Turbulence Model

Tilting pad bearings are appropriate for the trend of high efficiency and reliability design of rotating machinery due to their high stability. The laminar and turbulent flow states exist in the lubricating oil film of high-speed and heavy-load tilting pad bearings simultaneously. By perturbing the multiple flow state lubrication model with a partial derivative method, together with the pad-pivot structural perturbations, the frequency-dependent stiffness and damping coefficients of tilting pad bearings, embracing the effect of dynamical variations of both turbulence and pressure-viscous, were numerically solved in this research. The importance of each perturbed variable was studied, and the results indicate that the perturbed film thickness included in turbulence coefficients perturbations is significant enough to be taken into account otherwise the equivalent stiffness coefficients will be obviously overestimated. Unlike the perturbed film thickness, the consideration of the perturbed viscosity is optional, because it makes the stiffness and damping coefficients larger at both laminar and turbulent flow states. For a simplified simulation and conservative prediction results, the perturbed viscosity can be neglected.

CALCULATIONS OF TILTING-PAD THRUST BEARINGS

The application of thrust bearings in different engineering designs generates problems of thermal state, which generates the wear of the fixed or tilting pads of bearings. These problems can be avoided by means of proper methods and numerical algorithms of calculations of the bearing static characteristics, including the maximum oil film temperature. The knowledge of thermal state of bearings should assure safe, reliable, and durable bearing operation and is important for the designers of thrust bearings. This paper presents the results of calculations of some static characteristics of a tilting-pad thrust bearing, including its maximum oil film temperature. Numerical solution by means of finite differences was applied for the solution of geometry, Reynolds, energy, and viscosity equations. Adiabatic oil film laminar flow in the bearing gap was considered. The developed code of the computation of bearing performances creates a tool that leads to the solution of thermal problems. Different values of operating speeds were assumed.

Measuring the Fluid Film Thickness and Evaluation of Slope Parameter to Assess the Tribological Characteristics of Tilting Pad Bearings

Measuring the Fluid Film Thickness and Evaluation of Slope Parameter to Assess the Tribological Characteristics of Tilting Pad Bearings

Measuring the Fluid Film Thickness and Evaluation of Slope Parameter to Assess the Tribological Characteristics of Tilting Pad Bearings

Measuring the Fluid Film Thickness and Evaluation of Slope Parameter to Assess the Tribological Characteristics of Tilting Pad Bearings

Thermo-hybrid lubrication FSI-CFD model for the static characteristics of hybrid porous tilting pad bearings

Hybrid porous tilting pad bearing (HPTPB) is a new hybrid lubrication bearing showing potential for oil-free high-speed turbomachinery with reliable stability. This study presents a thermo-hybrid lubrication FSI-CFD model for HPTPB static characteristics. The interaction between the gas lubrication and the adaptive pad motion is solved with dynamic mesh iterative algorithm. The influences of rotor speed, supply pressure, radial stiffness, tilting stiffness, and nominal clearance on the load capacity, mass leakage, friction torque, and temperature rise are investigated. The adaptive pad motions significantly influence the hybrid lubrication of the hydrostatic and hydrodynamic effects in the HPTPB. With the complex bearing configuration, the static performances of HPTPB depend on the combined effect of the design parameters.

Approximation of Non-Linear Rotor Dynamic Resonance Behavior of Vertically Aligned Hydro-Units Guided by Tilting-Pad Bearings

Dynamic analyses of vertical hydro power plant rotors require the consideration of the non-linear bearing characteristics. This study investigates the vibrational behavior of a typical vertical machine using a time integration method that considers non-linear bearing forces. Thereby, the influence of support stiffness and unbalance magnitude is examined. The results show a rising influence of unbalance on resonance speed with increasing support stiffness. Furthermore, simulations reveal that the shaft orbit in the bearing is nearly circular for typical design constellations. This property is applied to derive a novel approximation procedure enabling the examination of non-linear resonance behavior, using linear rotor dynamic theory. The procedure considers the dynamic film pressure for determining the pad position. In addition, it is time-efficient compared to a time integration method, especially at high amplitudes when damping becomes small.

Thermohydrodynamic investigation for supercritical carbon dioxide high speed tilting pad bearings considering turbulence and real gas effect

A global heat balance method for supercritical carbon dioxide (S-CO2) high speed tilting pad bearings was developed, in which the real gas effect, variable thermodynamic properties, and turbulence effect were considered. The bearing characteristics can be obtained by the partial derivative method embracing dynamic variations of complete variables. Then thermohydrodynamic lubrication mechanisms for S-CO2 bearings are studied, and results indicate that the real gas effect of thermal compressibility is significant. The influence of the thermal effect on the static and dynamic characteristics of bearings is caused by changes in density, specific heat, and thermal expansion coefficient rather than viscosity, which is totally different from oil bearings. In general, the influence of thermohydrodynamic lubrication on static characteristics of S-CO2 tilting pad bearings is more obvious than that on dynamic coefficients. For example, the maximum deviation of damping coefficients of a bearing with parameters in this research at a certain speed range is 8%, and that of the load capacity at the corresponding speed is 10.7%. However, the influence of the thermal effect on dynamic coefficients is varied at different rotating speeds.

Tilt Pad Bearing Distributed Pad Inlet Temperature With Machine Learning—Part II: Morton Effect

Abstract The Morton effect (ME) occurs when a bearing journal experiences asymmetric heating due to synchronous vibration, resulting in thermal bowing of the shaft and increasing vibration. An accurate prediction of the journal's asymmetric temperature distribution is critical for reliable ME simulation. This distribution is strongly influenced by the film thermal boundary condition at the pad inlets. Part I utilizes machine learning (ML) to obtain a two-dimensional radial and axial distribution of temperatures over the leading-edge film cross section. The hybrid finite volume method (FVM)—bulk flow method of Part I eliminated film temperature discontinuities and is utilized in Part II for improving accuracy and efficiency of ME simulation.

Tilt Pad Bearing Distributed Pad Inlet Temperature With Machine Learning—Part I: Static and Dynamic Characteristics

AbstractUncertainty in mixing coefficients (MCs) for estimating pad leading-edge film temperature in tilt pad journal bearings reduces the reliability of predicted characteristics. A three-dimensional hybrid between pad (HBP) model, utilizing computational fluid dynamics (CFD) and machine learning (ML), is developed to provide the radial and axial temperature distributions at the leading edge. This provides an ML derived, two-dimensional film temperature distribution in place of a single uniform temperature. This has a significant influence on predicted journal temperature, dynamic coefficients, and Morton effect response. An innovative finite volume method (FVM) solver significantly increases computational speed, while maintaining comparable accuracy with CFD. Part I provides methodology and simulation results for static and dynamic characteristics, while Part II applies this to Morton effect response.

Reducing Vibrations Generated in a Gas Turbine Model MS9001E Used in South Baghdad Power Plant Station by Improving the Design of Bearings with Damper

Gas turbines are engines an energy plant makes use of for generating the rotary motion to show power generators. The gas turbine is largely a combustion engine for changing natural gas or different liquid fuels to rotational mechanical energy. Often, the gas turbine generates excessive noise or vibrations. In this work, the problem of vibrations occurrence in the gas turbine model MS9001E used in the south Baghdad power station is solved. This is done by making a groove in the bearing pad to increase the oil flow, replacing the bearing type with a tilt-pad bearing type with damper. The finite element method was used in the analysis process by ANSYS program. The results showed a decrease in the values of vibration amplitude, total deformation, stress, and strain.

A full 3D computational model for tilting-pad journal bearings and comparing it to 2D models

In this paper, a new model is developed to analyze a tilting pad bearing with 5 pads in a load-between-pad configuration in three dimensions. Isothermal Navier-Stokes equations with phase fraction equation for cavitation model are solved for 3D steady state simulation using the OpenFOAM package. Results show that with decrease in eccentricity, the difference between the 3D and 2D simulations increases. This is mainly due to the fluid inertia effects when entering the pads. Although applying the inertial boundary condition to the 2D model reduces the discrepancy, the difference in pressure distribution remains. Thus, at the lower eccentricity ratio, it is highly recommended to use 3D model in order to calculate pressure distribution precisely in tilting pad journal bearing.

Rotordynamic Characterization of Tilting-Pad Bearings With Eight Pads in Vertical Rotors

Abstract It has been documented that stiffness and damping for a four-pad bearing are dependent not only on the magnitude of the load but also on the position of the rotor in the bearing. However, eight-pad bearings are not commonly employed on horizontal turbines, and the presence of several pads in the bearing will decisively affect the dynamics of the system. This paper evaluates the stiffness and damping coefficients of tilting-pad bearings with eight pads and explores the main frequencies acting on the forced response of a vertical rotor. The bearing properties were modeled as a function of eccentricity and position in the stationary coordinate system by Navier–Stokes equations whose results are taken from commercial software. The simulated unbalanced response is compared to experimental results; the changing position of the shaft produces a periodic stiffness and damping, which is dependent on the number of pads. Cross-coupled coefficients influence is discussed, showing that their absence makes an accurate model for the mean values. The results indicate that simulation of vertical rotors with eight-pad bearings can be simplified which allow more effective simulations and dynamic analysis.

Experimental and theoretical investigation on rotodynamic characterization of hybrid porous tilting pad bearings

Porous journal gas bearings, which offer advantages of high load capacity and good stiffness compared to other types of hydrostatic gas bearings, will meet instability issues at high rotational speeds. Hybrid porous tilting pad bearings (HPTPBs) provide a possibility as a rotor supported in high-speed Turbomachinery. This study presents an experimental investigation of the dynamic responses of a rigid rotor supported with two HPTPBs. The rotor was successfully accelerated to 40 krpm. The supply pressure ratio of each pad is monitored separately, and the influence of the separate gas supply on the dynamic response is analyzed. Rotor dynamic tests with different unbalance mass and different supply pressure ratios were carried out. A mathematical model with the consideration of airflows in the porous materials and bearing clearance, pad motion, rotor motion, unbalance force were presented. Prediction results are accorded well with the test results.

Development of A High-Load Capacity Test Rig to Evaluate the Static Performance of Process Fluid-Lubricated Thrust Bearings

Electrical submersible pumps (ESPs) are artificial lift devices widely used in the oil and gas industry to increase production. For unconventional wells, which includes subsea applications, installation cost is an order of magnitude higher than the cost of the typical ESP, thus pump reliability is paramount. Contamination of the thrust bearing lubricant oil by process fluid due to seal failures is one of the leading causes of thrust bearing failure. While improving seal reliability can prevent thrust bearing failures, an alternative approach is to develop process-fluid lubricated thrust bearings. This research aims to characterize and study the performance of thrust bearings operating with process fluid lubrication. A component level-level test rig for testing the performance of thrust bearings in any mixture of water, sand, and air is designed, built, and commissioned. Initial tests of the PEEK and Tungsten Carbide (WC) bearings include a load capacity test to determine the hydrodynamic limit of the bearing, a hydrodynamic test to corroborate test rig stability, and a wear test to determine if the bearings can operate feasibly past hydrodynamic limits in a mixed lubrication regime. Initial results show that lubrication starvation can occur in an unpressurized chamber for low viscosity fluids that are not supplied directly to the bearing. Furthermore, the film thickness, temperature rise in the pads, and load capacity all are lower for water lubricated bearings when compared to oil lubricated bearings. Results suggest that liner material affects wear rate but not load capacity; however, operating even the WC bearings past hydrodynamic limits causes substantial wear and is not recommended as an operating mode. Polycrystalline Diamond (PCD) coated mixed lubrication bearings were also tested. These bearings, although requiring higher drive torque, sustained higher loads than the tilting pad bearings without significant wear