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

2020 ◽  
Vol 142 (12) ◽  
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 rotor-dynamic 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-elastohydrodynamic (TEHD) 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.

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.

Identification of Dynamic Coefficients of a Five-Pad Tilting Pad Journal Bearing up to Highest Surface Speeds

2020 ◽  
Author(s):  
Philipp Zemella ◽  
Thomas Hagemann ◽  
Bastian Pfau ◽  
Hubert Schwarze
Keyword(s):  
Flow Rate ◽  
Time Domain ◽  
Static Load ◽  
Journal Bearing ◽  
Damping Coefficients ◽  
Dynamic Coefficients ◽  
Tilting Pad ◽  
Oil Flow ◽  
Tilting Pad Journal Bearing ◽  
The Impact

Abstract Tilting-pad journal bearings are widely used in turbomachinery industry due to their positive dynamic properties at high rotor speeds. However, the exact description of this dynamic behavior is still part of current research. This paper presents measurement results for a five-pad tilting-pad journal bearing in load between pivot configuration. The bearing is characterized by a nominal diameter of 100 mm, a length of 90 mm, and a pivot offset of 0.6. Investigations include results for surface speeds between 25 and 120 m/s and specific bearing loads ranging from 0.0 to 3.0 MPa. Results of theoretical predictions are commonly derived from perturbation of stationary operation under static load. Therefore, experimental results for stationary operation including pad deflection under static load are presented first to characterize the investigated bearing. Measured results indicate considerable non-laminar flow in the upper region of the investigated range of rotor speeds. Second, dynamic excitation test are performed with excitation frequencies up to 400 Hz to evaluate dynamic coefficients of a stiffness (K) and damping (C) KC-model, and additionally, a KCM-model using additional virtual mass (M) coefficients. KCM-coefficients are obtained by fitting frequency dependent KC-characteristics to the KCM-model structure using least square approach. The wide range of rotating and excitation frequencies leads to subsynchronous as well as supersynchronous vibrations. Excitation forces are applied with multi-sinus and single-sinus characteristics. The latter one allows evaluation of KC-coefficients at the particular frequency ratio in the time domain. Here, frequency and time domain evaluation algorithms for dynamic coefficients are used in order to assess their special properties and quality. The impact of surface speed, bearing load, and oil flow rate on measured and predicted KCM-coefficients is investigated. Measured and predicted results can be well fitted to a KCM-model and show a significant influence of the ratio between fluid film and pivot support stiffness on the speed dependent characteristic of bearing stiffness coefficients. However, the impact of this ratio on damping coefficients is considerably lower. Further investigations on the impact of oil flow rates indicate that a significant decrease of direct damping coefficients exists below a certain level of starvation. Above this limit, direct damping coefficients are nearly independent of oil flow rate. Results are analyzed in detail and demands on improvements for predictions are derived.

Effect of Pad Material, Copper vs. Steel, on the Performance of a Tilting Pad Journal Bearing: Measurements and Predictions

2021 ◽  
Author(s):  
Luis San Andrés ◽  
Hussain Kaizar ◽  
Hardik Jani ◽  
Manish Thorat
Keyword(s):  
Temperature Rise ◽  
High Surface ◽  
Operating Conditions ◽  
Radial Clearance ◽  
Maximum Difference ◽  
Shaft Speed ◽  
Damping Force ◽  
Damping Coefficients ◽  
Tilting Pad ◽  
Exit Temperature

Abstract High temperature operation limits the life of fluid film bearings; hence the need to quantify the effect of pad material on the performance of tilting pad journal bearings (TPJBs). The paper presents measurements of performance conducted on a copper-pads bearing (C-PB) and a steel-pads bearing (S-PB). Both bearings have the same geometry and differ on the pads’ backing material, copper vs. steel, and slightly in the assembled cold clearance. The journal diameter D = 102 mm, and a bearing has five pads with length L = 0.4D, nominal radial clearance 0.064 mm, and pad preload of 0.42. The pads are 12.3 mm in thickness and have a 50% offset pivot, ball-in-socket type. The bearings operate at four shaft speeds ranging from 6 krpm (32 m/s surface speed) to 14 krpm (74 m/s) and under multiple specific loads ranging from 0.17 MPa to 2.1 MPa. ISO VG 32 oil, at a supply temperature of 49 °C, lubricates a test bearing configured with end seals (flooded bearing). At the highest load (on pad) and low shaft speed, the S-PB static eccentricity is up to 37% higher than that for the C-PB. The oil exit temperature rise is similar for both bearings, the maximum difference reaches 6 °C. For all operating conditions, the pads’ peak temperature rise, having a maximum difference of 5 °C to 16 °C, is larger for the S-PB. The S-PB produces a ∼ 5% lower drag power loss than that in the C-PB. Drag power in both bearings increases with shaft speed and is largely independent of applied load. From dynamic load tests with multiple excitation frequencies to 250 Hz, the C-PB direct stiffness KYY (along the load direction) is up to 30% higher than the S-PB stiffness, while the difference in KXX between the C-PB and the S-PB ranges from 60% to 90%. Similar to the stiffness results, the C-PB produces larger direct damping coefficients; CYY and CXX are up to 25% and 40% larger than those for the S-PB. Both bearings, however, show symmetry in the damping coefficients, i.e., CXX ∼ CYY. Virtual mass coefficients (MXX, MYY) are significant in magnitude though having a large uncertainty. A computational physics model predicts the TPJB performance under identical conditions. The exhaustive comparison conducted with a sound dimensional characterization of parameters reveals that predictions agree well with measurements of journal eccentricity, oil exit temperature, pad surface temperatures, and stiffness and damping force coefficients. The differences amount to 20% or less. The model relies on specifying the material properties for pads and pivots and the operating (hot) clearance to produce accurate thermo-mechanically induced deformations that affect bearing performance at high loads and high surface speed operation.

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.

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.

Study on Subsynchronous Vibration With Tilting Pad Journal Bearing Under Starved Lubrication

2018 ◽  
Author(s):  
Rimpei Kawashita ◽  
Tadasuke Nishioka ◽  
Shimpei Yokoyama ◽  
Makoto Iwasaki ◽  
Shuichi Isayama ◽  
...  
Keyword(s):  
Flow Rate ◽  
Journal Bearing ◽  
Damping Ratio ◽  
Leading Edge ◽  
Rotor System ◽  
Experimental Results ◽  
Oil Film ◽  
Tilting Pad ◽  
Oil Flow ◽  
Starved Lubrication

Industrial machines such as gas and steam turbines require high efficiency and reliability. Direct lubricated bearings have been developed and installed to reduce mechanical losses. In recent years, it has been reported in the literature that subsynchronous vibration can occur to rotor shafts with direct lubricated tilting pad journal bearings under reduced oil flow rate conditions. In this study, a test rig with a 200 mm diameter and 3.5 meter long rotor supported by a direct lubricated tilting two pad journal bearing was constructed. The primary critical speed is 2100rpm and rotational speed is 3600rpm. The oil-starved area, the non-oil film layer region at the leading edge of the bearing pads, was measured by observing oil film pressure in the bearing clearance with pressure transducers on the rotor surface. A sine sweep excitation test was carried out by using an inertial shaker installed on the bearing housing and the damping ratio of the rotor system was measured. Measured data showed that a larger starved area at the leading edge of the bearing pads due to reduced oil feeding results in a smaller damping ratio, and an increase in the natural frequency of the rotor. Experimental results of two types of oil feeding nozzles were compared with respect to the correlation between starved area and damping ratio of the rotor system, and a relationship between oil flow rate and starved area was discussed. A method for modeling bearing coefficients under starved lubrication has been proposed based on thermo-hydrodynamic lubrication (THL) analysis. A numerical analysis of a finite element-transfer matrix model of the test rotor with the bearing coefficients calculated by the proposed method is carried out, and it is found that the analytical results are in broad agreement with the experimental results.

Design of Efficient Turbulent Thrust Bearings III. Self-Pressurized Design

1981 ◽  
Vol 103 (3) ◽  
pp. 459-466
Author(s):  
D. F. Wilcock
Keyword(s):  
Temperature Rise ◽  
Power Loss ◽  
Power Efficiency ◽  
High Speed ◽  
Hybrid Design ◽  
Thrust Bearings ◽  
Higher Power ◽  
Hydrostatic Load ◽  
Oil Flow ◽  
Higher Temperature

Turbulence makes high speed conventionally designed bearings operate with higher power loss, higher temperature rise, and lower oil flow than would be predicted from conventional laminar analysis. The objective of this paper is to present a new concept for increasing the load/power efficiency of large thrust bearings by a hybrid design employing hydrostatic load support combined with hydrodynamic pads. Self-pressurization using a shaft-center feed to radial ducts in the runner provides reliability fully equal to conventional bearing-fed designs.

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