Effect of Pad and Liner Material Properties on the Static Load Performance of a Tilting Pad Thrust Bearing

2019 ◽  
Vol 141 (12) ◽  
Author(s):  
Rasool Koosha ◽  
Luis San Andrés
Keyword(s):  
Film Thickness ◽  
Turbulent Flow ◽  
Temperature Rise ◽  
Power Loss ◽  
Fluid Film ◽  
Predictive Tool ◽  
Liner Material ◽  
Tilting Pad ◽  
Hard Polymer ◽  
Polymer Liner

AbstractTilting pad thrust bearings (TPTBs) control rotor axial placement in rotating machinery, and their main advantages include low drag power loss, simple installation, and low-cost maintenance. The paper details a novel thermo-elasto-hydrodynamic (TEHD) analysis predictive tool for TPTBs that considers a three-dimensional (3D) thermal energy transport equation in the fluid film, coupled with heat conduction equations in the pads, and a generalized Reynolds equation with cross-film viscosity variation. The predicted pressure field and temperature rise are employed in a finite element (FE) structural model to produce 3D elastic deformation fields in the bearing pads. Solutions of the governing equations delivers the operating film thickness, required flowrate, and shear drag power loss, and the pad and lubricant temperature rises as a function of an applied load and shaft speed. To verify the model, predictions of pad subsurface temperature are benchmarked against published test data for a centrally pivoted eight-pad TPTB with 267 mm in outer diameter (OD) operating at 4–13 krpm (maximum surface speed = 175 m/s) and under a specific load ranging from 0.69 to 3.44 MPa. The current TEHD temperature predictions match well the test data with a maximum difference of 4 °C and 11 °C (<10%) at laminar and turbulent flow conditions, receptively. Next, the TEHD predictive tool is used to study the influence of both pad and liner material properties on the performance of a TPTB. The analysis takes a whole steel pad (without a liner or babbitt), a steel pad with a 2-mm-thick babbitt layer (common usage), a steel pad with a 2-mm-thick hard-polymer (polyether ether ketone, e.g., PEEK®) liner, and a pad entirely made of hard-polymer material, whose elastic modulus is just 12.5 GPa, only 6% that of steel. The bare steel pad reveals the poorest performance among all the pads as it produces the smallest fluid film thickness and consumes the largest drag power loss. For laminar flow operations (Reynolds number Re < 580), the babbitted-steel pad operates with the thickest fluid film and the lowest film temperature rise. For turbulent flow conditions Re > 800, the solid hard-polymer pad, however, shows a 23% thicker film than that in the babbitted pad and produces up to 25% lesser drag power loss. In general, the solid hard-polymer TPTB is found to be a good fit for operation at a turbulent flow condition as it shows a lower drag power loss and a larger film thickness; however, its demand for a too large supply flowrate is significant. Predictions for steel pads with various hard-polymer liner and babbitt thicknesses demonstrate that using a hard-polymer liner, instead of white metal, isolates the pad from the fluid film and results in an up to 30 °C (50%) lower temperature rise in the pads than that for a babbitted-steel pad. For operations under a heavy specific load (>3.0 MPa), however, a thick hard-polymer liner extensively deforms and results in a small film thickness.

Effect of Pad and Liner Material Properties on the Static Load Performance of a Tilting Pad Thrust Bearing

2019 ◽  
Author(s):  
Rasool Koosha ◽  
Luis San Andrés
Keyword(s):  
Film Thickness ◽  
Turbulent Flow ◽  
Temperature Rise ◽  
Power Loss ◽  
Fluid Film ◽  
Predictive Tool ◽  
Liner Material ◽  
Tilting Pad ◽  
Hard Polymer ◽  
Polymer Liner

Abstract Tilting Pad Thrust Bearings (TPTBs) control rotor axial placement in rotating machinery and their main advantages include low drag power loss, simple installation, and low-cost maintenance. The paper details a novel thermo-elasto-hydrodynamic (TEHD) analysis predictive tool for TPTBs that considers a 3D thermal energy transport equation in the fluid film, coupled with heat conduction equations in the pads, and a generalized Reynolds equation with cross-film viscosity variation. The predicted pressure field and temperature rise are employed in a finite element structural model to produce 3D elastic deformation fields in the bearing pads. Solutions of the governing equations delivers the operating film thickness, required flow rate, shear drag power loss, and the pad and lubricant temperature rises as a function of an applied load and shaft speed. To verify the model, predictions of pad sub-surface temperature are benchmarked against published test data for a centrally pivoted eight-pad TPTB with 267 mm in outer diameter operating at 4–13 krpm (maximum surface speed = 175 m/s) and under a specific load ranging from 0.69 to 3.44 MPa. The current TEHD temperature predictions match well the test data with a maximum difference of 4°C and 11°C (< 10%) at laminar and turbulent flow conditions, receptively. Next, the TEHD predictive tool is used to study the influence of both pad and liner material properties on the performance of a TPTB. The analysis takes a whole steel pad (without a liner or babbitt), a steel pad with a 2 mm thick babbitt layer (common usage), a steel pad with a 2 mm thick hard-polymer (polyether ether ketone, e.g PEEK®) liner, and a pad entirely made of hard-polymer material, whose elastic modulus is just 12.5 GPa, only 6% that of steel. The bare steel pad reveals the poorest performance among all the pads as it produces the smallest fluid film thickness and consumes the largest drag power loss. For laminar flow operations (Reynolds number Re < 580), the babbitted-steel pad operates with the thickest fluid film and the lowest film temperature rise. For turbulent flow conditions Re > 800, the solid hard-polymer pad, however, shows a 23% thicker film than that in the babbitted pad and produces up to 25% lesser drag power loss. In general, the solid hard-polymer TPTB is found to be a good fit for operation at a turbulent flow condition as it shows a lower drag power loss and a larger film thickness, however, its demand for a too large supply flow rate is significant. Predictions for steel pads with various hard-polymer liner and babbitt thicknesses demonstrate that using a hard-polymer liner, instead of white metal, isolates the pad from the fluid film and results in an up to 30°C (50%) lower temperature rise in the pads than that for a babbitted-steel pad. For operations under a heavy specific load (> 3.0 MPa), however, a thick hard-polymer liner extensively deforms and results in a small film thickness.

Response Surface Mapping and Multi-Objective Optimization of Tilting Pad Bearing Designs

2017 ◽  
Author(s):  
Michael Branagan ◽  
Neal Morgan ◽  
Brian Weaver ◽  
Houston Wood
Keyword(s):  
Film Thickness ◽  
Power Loss ◽  
Performance Metrics ◽  
Optimization Methods ◽  
Fluid Film ◽  
Design Variables ◽  
Tilting Pad ◽  
Bearing Design ◽  
Central Composite

Fluid film bearings for turbomachinery are designed to support the loads applied by the rotor system, often at high speeds when power loss in the bearing becomes significant and bearing temperatures can reach levels that can be detrimental to the long-term reliability of the support system. These requirements of supportive bearings require an intimate understanding of how bearing design variables affect their overall performance. Ideal bearings minimize power loss to increase machine efficiency and maintain low operating temperatures to ensure long-term reliability while meeting other design criteria such as minimum film thickness to provide proper support and avoiding high fluid pressures that can be harmful to the bearing structure. However, real world designs are often forced to sacrifice some of these design goals in order to preserve others. Therefore, further understanding of the relative opportunity costs associated with optimizing the bearing design with differently weighted performance metrics and their relationships to bearing design variables is invaluable to design engineers. This study explores the impact of eight bearing design variables on the performance of two tilting pad journal bearings supporting an eight-stage centrifugal compressor using design of experiments techniques applied to an established thermoelastohydrodynamic (TEHD) bearing model of tilting pad bearing performance. The bearing design variables analyzed include the radial clearance, pad arc spacing, pad axial length, pivot offset, preload, working fluid viscosity and viscosity index, and the number of pads. Each of the design variables — excluding the number of pads which was realistically constrained — were first varied over five levels each in a central composite design. These central composite designs were repeated for each of three values for number of pads. The responses obtained from the TEHD numerical simulations for each bearing design point were power loss, maximum pad temperature, minimum film thickness, and maximum fluid film pressure. The results from the central composite studies were fit with a multivariate least-squares regression model and a secondary series of experimental design studies were simulated around potential optimum design points to obtain a learning set to initialize direct optimization methods. Two direct multi-objective optimization methods, a sequential quadratic programming method and a multi-island genetic algorithm, were performed using Isight, a commercial software. A range of weighting parameters were selected for the optimization functions to find bearing designs that minimized power loss and pad temperature while maintaining pressure and film thickness criteria within acceptable design ranges for fluid film bearings. The resulting optimum design points allowed for a comparison between the design optimization approaches. The various strengths and weaknesses of the different methods are discussed. This study demonstrates how designers can use these approaches to view the relationships between design variables and important performance metrics to design better bearings for a wide range of applications.

A Model for Tilting Pad Thrust Bearings Operating With Reduced Flow Rate – Do Benefits Outweigh Risks?

2021 ◽  
Author(s):  
Rasool Koosha ◽  
Luis San Andrés
Keyword(s):  
Film Thickness ◽  
Flow Rate ◽  
Temperature Rise ◽  
Thrust Bearings ◽  
Flow Reduction ◽  
Tilting Pad ◽  
Minimum Film Thickness ◽  
Nominal Rate ◽  
Thrust Pad ◽  
Reduced Flow

Abstract The literature on tilting pad thrust bearings (TPTB) calls for flow reduction as an effective means to reduce drag power losses as well as oil pumping costs. However, the highest level of flow reduction a bearing can undergo while maintaining reliable operation is a key question that demands comprehensive analysis. This paper implements a model into an existing thermoelasto-hydrodynamic (TEHD) computational analysis tool to deliver load performance predictions for TPTBs operating with reduced flow rates. For bearings supplied with either a reduced flow or an over flow conditions, a sound model for the flow and thermal energy mixing in a feed groove determines the temperature of the lubricant entering a thrust pad. Under a reduced flow condition, the analysis reduces the effective arc length of a wetted pad until matching the available flow. Predicted discharge flow temperature rise and pad subsurface temperature rise from the present model match measurements in the archival literature for an eight-pad bearing supplied with 150% to 25% of the nominal flow rate, i.e., the minimum flow that fully lubricates the bearing pads. A supply flow above nominal rate increases the bearing drag power because the lubricant enters a pad at a lower temperature, and yet has little effect on a thrust pad peak temperature rise or its minimum film thickness. A reduced flow below nominal produces areas lubricant starvation zones, and thus the minimum film thickness substantially decreases while the film and pad’s surface temperature rapidly increase to produce significant thermal crowning of the pad surface. Compared to the bearing lubricated with a nominal rate, a starved flow bearing produces a larger axial stiffness and a lesser damping coefficient. A reduction in drag power with less lubricant supplied brings an immediate energy efficiency improvement to bearing operation. However, sustained long-term operation with overly warm pad temperatures could reduce the reliability of the mechanical element and its ultimate failure.

Two Dimensional Analytical Analysis of Fluid Film Thickness on Pivoting Tilting Pad Bearings

2007 ◽  
Author(s):  
Weishun William Ni ◽  
Christian L. Griffiths ◽  
Daniel J. Bartholme ◽  
Richard Hergert
Keyword(s):  
Film Thickness ◽  
Fluid Film ◽  
Two Dimensional ◽  
Analytical Analysis ◽  
Tilting Pad ◽  
Tilting Pad Bearings ◽  
Fluid Film Thickness

scholarly journals On the Possibilities of Decreasing Power Loss in Large Tilting Pad Thrust Bearings

2013 ◽  
Vol 2013 ◽  
pp. 1-9 ◽  
Author(s):  
Michal Wasilczuk ◽  
Grzegorz Rotta
Keyword(s):  
Power Loss ◽  
Power Plants ◽  
Thrust Bearing ◽  
Fluid Film ◽  
Total Power ◽  
Thrust Bearings ◽  
Oil Supply ◽  
Water Power ◽  
Lubricant Flow ◽  
Tilting Pad

Different systems of direct oil supply have been developed in order to facilitate efficient introduction of fresh lubricant to the oil gap and reduction of churning power loss in tilting pad thrust bearings. Up to now there is no documented application of the supply groove in large thrust bearings used in water power plants. The results of modeling lubricant flow in the lubricating groove of a thrust bearing pad will be presented in the paper. CFD software was used to carry out fluid film calculations. Such analysis makes it possible to modify groove geometry and other parameters and to study their influence on bearing performance. According to the results a remarkable decrease in total power loss due to avoiding churning losses can be observed in the bearing.

On the Effect of Supplied Flow Rate to the Performance of a Tilting-Pad Journal Bearing: Static Load and Dynamic Force Measurements

2020 ◽  
Author(s):  
Luis San Andrés ◽  
Hardik Jani ◽  
Hussain Kaizar ◽  
Manish Thorat
Keyword(s):  
Flow Rate ◽  
Temperature Rise ◽  
Power Loss ◽  
Static Load ◽  
Dynamic Force ◽  
Shaft Speed ◽  
Tilting Pad ◽  
Oil Flow ◽  
Exit Temperature ◽  
Subsurface Temperatures

Abstract Rotating machinery relies on engineered tilting-pad journal bearings (TPJB) to provide static load support with minimal drag power losses, safe pad temperatures, and ensuring a rotordynamic stable rotor operation. End users focus on reducing the supplied oil flow rate into a bearing to both lower operational costs and to increase drive power efficiency. This paper presents measurements of the steady-state and dynamic forced performance of a TPJB whilst focusing on the influence of supplied oil flow rate, below and above a nominal condition (50% and 150%). The test bearing has five pads, slenderness ratio L/D = 0.4, spherical pivots with pad offset = 50% and a preload ∼ 0.40, with a clearance to radius ratio (Cr/R) ≈ 0.001 at room temperature. The bearing is installed under a load-between-pads (LBP) orientation and has a flooded housing with end seals. The test conditions include operation at various shaft surface speeds (32 m/s-85 m/s) and specific static loads from 0.17 MPa to 2.1 MPa. A turbine oil lubricates the bearing with a speed-dependent flow rate delivered at a constant supply temperature. Measurements obtained at a steady thermal equilibrium include the journal static eccentricity and attitude angle, the oil exit temperature rise, and the pads’ subsurface temperatures at various locations, circumferential and axial. The rig includes measurement of the drive torque and shaft speed to produce the bearing drag power loss. Dynamic force coefficients include stiffness, damping, and virtual-mass coefficients. As expected, the drag power and the lubricant temperature rise depend mainly on shaft speed rather than on applied load. A reduction in oil flow rate to 50% of its nominal magnitude causes a modest increase in journal eccentricity, a 15% reduction in drag power loss, a moderate raise (6°C) in pads’ subsurface temperatures, a slight increase (up to 6%) in the direct stiffnesses, and a decrease (up to 7%) in direct damping coefficients. Conversely, a 1.5 times increase in oil flow rate causes a slight increase (up to 9 %) in drag power loss, a moderate reduction of pads’ temperatures (up to 3°C), a maximum 5% reduction in direct stiffnesses, and a maximum 10% increase in direct damping. The paper also presents comparisons of the test results against predictions from a thermo-elasto-hydrodynamic lubrication model. In conclusion, a 50% reduced oil flow rate only causes a slight degradation in the test bearing static and dynamic force performance and does not make the bearing operation unsafe for tests with surface speed up to 74 m/s. As an important corollary, the measured bearing drag power differs from the conventional estimate derived from the product of the supplied flow rate, the lubricant specific heat and the oil exit temperature rise.

A Thermoelastohydrodynamic Analysis for the Static Performance of High-Speed Heavy Load Tilting-Pad Journal Bearing Operating in the Turbulent Flow Regime and Comparisons to Test Data

2018 ◽  
Author(s):  
Hirotoshi Arihara ◽  
Yuki Kameyama ◽  
Yoshitaka Baba ◽  
Luis San Andrés
Keyword(s):  
Turbulent Flow ◽  
Flow Regime ◽  
Flow Rate ◽  
Power Loss ◽  
High Speed ◽  
Hydrodynamic Pressure ◽  
Thermally Induced ◽  
Turbulent Flow Regime ◽  
Tilting Pad ◽  
Static Performance

Tilting-pad journal bearings (TPJBs) ensure rotordynamic stability that could otherwise produce dangerously large amplitude rotor oil-whirl/whip motions in high speed rotating machinery. Currently, highly efficient turbo compressors demand an ever increasing rotor surface speed and specific load on its support bearings. The accurate prediction of bearing performance is vital to guarantee reliable products, specifically with regard to reducing maximum bearing pad temperature and drag power losses, and operating with the least flow rate while still maximizing load capacity. The hydrodynamic pressure and heat generation in an oil film acting on a bearing pad produce significant mechanical and thermal deformations that change the oil film geometry (clearance and preload) to largely affect the bearing performance, static and dynamic. In addition, a high surface speed bearing often operates in the turbulent flow regime that produces a notable increase in power loss and a drop in maximum pad temperature. This paper details a thermoelastohydrodynamic (TEHD) analysis model applied to TPJBs, presents predictions for their steady-load performance, and discusses comparisons with experimental results to validate the model. The test bearing has four pads with a load between pads configuration; its length L = 76.2 mm and shaft diameter D = 101.6 mm (L/D = 0.75). The rotor top speed is 22.6 krpm, i.e. 120 m/s surface speed, and the maximum specific load is 2.94 MPa for an applied load of 23 kN. The test procedure records shaft speed and applied load, oil supply pressure/temperature and flow rate, and also measures the pads’ temperature and shaft temperature, as well as the discharge oil (sump) temperature. The TEHD model couples a generalized Reynolds equation for the hydrodynamic pressure generation with a three-dimensional energy transport equation for the film temperature. The pad mechanical deformation due to pressure utilizes the finite elemental method, whereas an analytical model estimates thermally induced pad crowning deformations. For operation beyond the laminar flow regime, the analysis incorporates the eddy viscosity concept for fully developed turbulent flow operation. Current predictions demonstrate the influence of pressure and temperature fields on the pads mechanical and thermally induced deformation fields, and also show static performance characteristics such as bearing power loss, flow rate, and pad temperatures. The comparisons of test results and analysis results reveal that turbulent flow effects significantly reduce the pads’ maximum temperature while increasing the bearing power loss. Turbulent flow mixing increases the diffusion of thermal energy and makes more uniform the temperature profile across the film.

scholarly journals Study of the influence of slipper parameters on the power efficiency of axial piston pumps

2018 ◽  
Vol 10 (9) ◽  
pp. 168781401880146 ◽  
Author(s):  
Gaston Haidak ◽  
Dongyun Wang ◽  
E Shiju ◽  
Jun Liu
Keyword(s):  
Mathematical Model ◽  
Film Thickness ◽  
Power Loss ◽  
Power Efficiency ◽  
Fluid Film ◽  
Total Power ◽  
Axial Piston Pumps ◽  
Swash Plate ◽  
Fluid Film Thickness ◽  
Axial Piston

This article presents the influence and impact of the gap between the outer and the inner diameter of the slipper on the performance of axial piston pumps. For this, a mathematical model establishing and evaluating the quantities involved in the total power loss is established. Four slippers having a different values of the ratio between their diameters are considered; for which the study and the simulation concerning the fluid film thickness, the forces, the flow and the total power loss between the slipper and the swash plate are developed and compared. After the analysis of all these parameters for different slippers, the results of the simulation show that for each slipper, there are values of the optimum fluid film thickness for which the pump has the minimum in terms of power loss between the slipper and the swash plate. And after the comparison, the favourable ratio between the diameters of the slipper for good lubrication is given. The accuracy between the mathematical model and simulation results is checked, and a discussion is made. Finally, a conclusion based on the results of the lost power is made.

Characterization of Five-Pad Tilting-Pad Journal Bearings Using an Original Test-Rig

2011 ◽  
Author(s):  
S. Chatterton ◽  
P. Pennacchi ◽  
A. Vania ◽  
E. Tanzi ◽  
R. Ricci
Keyword(s):  
Film Thickness ◽  
Gas Turbines ◽  
Journal Bearings ◽  
Fluid Film ◽  
Test Rig ◽  
Theoretical Evaluation ◽  
Oil Film ◽  
Tilting Pad ◽  
Fluid Film Thickness ◽  
Tilting Pad Journal Bearings

Tilting-pad journal bearings are installed with increased frequency owing to their dynamic stability characteristics in several rotating machine applications, typically in high rotating speed cases. This usually happens for new installations in highspeed compressors or during revamping operations of steam and gas turbines for power generation. The selection from a catalogue, or the design of a new bearing, requires the knowledge of the bearing characteristics such as babbitt metal temperatures, fluid-film thickness, load capacity, stiffness and damping coefficients. Temperature and fluid-film thickness are essential for the safety of the bearing. Babbitt metal is subject to creep at high temperatures, as it happens at high speed operations. On the contrary, at low speed or with high loads, oil-film thickness could be too low, resulting in metal to metal contact. Oil-film dynamic coefficients are largely responsible of the dynamic behaviour and of the stability of the rotor-tilting-pad-bearing system. Therefore, the theoretical evaluation and/or the experimental estimation of these coefficients are mandatory in the design phase. The theoretical evaluation of these coefficients for tilting pad journal bearings is difficult due to their complex geometry, boundary and thermal conditions and turbulent flow, whereas an experimental characterization requires a suitable test rig. The paper describes the test rig designed to this purpose and its unusual configuration with respect to other test rigs available in literature. Some preliminary tests performed for the bearing characterization are also shown.

Influence of Turbulence on Performance Characteristics of the Tilting Pad Thrust Bearing

1974 ◽  
Vol 96 (1) ◽  
pp. 110-116 ◽  
Author(s):  
J. W. Capitao
Keyword(s):  
Turbulent Flow ◽  
Power Loss ◽  
Thrust Bearing ◽  
Load Capacity ◽  
Equal Area ◽  
Thrust Bearings ◽  
Finite Difference Equations ◽  
Tilting Pad ◽  
Oil Flow ◽  
Flow Theories

The influence of fluid film turbulence on the performance of centrally-pivoted tilting pad thrust bearings was analyzed. Major features of the analysis are: (1) today’s two predominant “engineering” turbulent flow theories are delineated and their quantitative predictions compared; (2) a spherical pad profile was assumed, and (3) an equal area technique was used in the finite difference equations. The results confirmed earlier predictions of increases in power loss and load capacity when compared to a laminar solution. Also, no significant differences were found between the results predicted by the two predominant turbulent flow theories. Power loss, load capacity, and hydrodynamic oil flow are given for 13, 15, and 17 in. sizes. Comparisons of laminar and turbulent numerical results are presented.

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