Measurements of Static and Dynamic Load Performance of a 102 mm Carbon-Graphite Porous Surface Tilting-Pad Gas Journal Bearing

2021 ◽  
Author(s):  
Luis San Andrés ◽  
Rachel Bolen ◽  
Jing Yang ◽  
Ryan McGowan
Keyword(s):  
Dynamic Load ◽  
Load Capacity ◽  
Stable Operation ◽  
Specific Load ◽  
Force Coefficients ◽  
Supply Pressure ◽  
Air Supply ◽  
Tilting Pad ◽  
Frequency Independent ◽  
Gas Bearing

Abstract Aerostatic journal bearings with porous tilting pads enable shaft support with minute drag power losses. To date archival information on the static and dynamic load performance of this bearing type is scant. Thus, the paper presents measurements conducted with an air lubricated bearing with diameter d = 102 mm and comprising four tilting pads made of porous carbon-graphite, each with length L = 76 mm. Two nested Belleville washers resting on spherical pivots support each pad. At ambient temperature of ∼ 21°C, as the air supply pressure into the bearing pads increases, so does the bearing aerostatic specific load (F/(L·d)) that reaches 58% of the pressure difference, supply minus ambient. With an air supply pressure of 7.8 bar(a), the test bearing static stiffness KS = 13.1 MN/m, is independent of both shaft speed and static load. KS is just 63% of the washers’ stiffness KP = 20.6 MN/m (during loading). While operating with shaft speeds equal to 6 krpm and 9 krpm (150 Hz) and under specific loads to 115 kPa and 101 kPa respectively, dynamic load experiments with excitation frequencies up to 342 Hz show the test bearing supplied with air at 7.8 bar(a) has frequency independent stiffness (K) and damping (C) coefficients. For rotor speeds equaling 0, 6 and 9 krpm, the bearing direct stiffnesses KXX ∼ KYY range from 13.6 MN/m to 32.7 MN/m as the specific load increases from 0 kPa to 115 kPa. The direct damping coefficients CXX ∼ CYY are as large as 5.8 kN·s/m, though having a large experimental uncertainty. Bearing cross-coupled force coefficients are insignificant. The test porous gas bearing reached its intended load capacity, demonstrated a dynamically stable operation and produced force coefficients mainly affected by the pads’ pivot supports and the magnitude of air supply pressurization.

Measurements of Static and Dynamic Load Performance of a 102 MM Carbon-Graphite Porous Surface Tilting-Pad Gas Journal Bearing

2021 ◽  
Author(s):  
Luis San Andres ◽  
Jing Yang ◽  
Ryan McGowan
Keyword(s):  
Dynamic Load ◽  
Load Capacity ◽  
Stable Operation ◽  
Specific Load ◽  
Damping Coefficients ◽  
Supply Pressure ◽  
Air Supply ◽  
Frequency Independent ◽  
Stiffness And Damping ◽  
Gas Bearing

Abstract Aerostatic journal bearings with porous tilting pads enable shaft support with minute drag power losses. To date archival information on the static and dynamic load performance of this bearing type is scant. Thus, the paper presents measurements conducted with an air bearing with diameter 102 mm and comprising four tilting pads made of porous carbon-graphite, each with length = 76 mm. At ambient temperature of 21°C, as the air supply pressure into the bearing pads increases, so does the bearing aerostatic specific load that reaches 58% of the pressure difference. With a supply pressure of 7.8 bar(a), the test bearing static stiffness = 13.1 MN/m, is independent of both shaft speed and static load. While operating with shaft speeds = 6 krpm and 9 krpm and under specific loads to 115 kPa and 101 kPa respectively, dynamic load experiments with excitation frequencies up to 342 Hz show the test bearing supplied with air at 7.8 bar(a) has frequency independent stiffness and damping coefficients. For rotor speeds equaling 0, 6 and 9 krpm, the bearing direct stiffnesses range from 13.6 MN/m to 32.7 MN/m as the specific load increases from 0 kPa to 115 kPa. The direct damping coefficients are as large as 5.8 kN·s/m. The test porous gas bearing reached its intended load capacity, demonstrated a dynamically stable operation and produced force coefficients mainly affected by the pads' pivot supports and the magnitude of air supply pressurization.

Experimental Identification of Dynamic Force Coefficients for a 110 mm Compliantly Damped Hybrid Gas Bearing

2014 ◽  
Author(s):  
Adolfo Delgado
Keyword(s):  
Load Capacity ◽  
Excitation Frequency ◽  
Dynamic Test ◽  
Inlet Pressure ◽  
Dynamic Force ◽  
Metal Mesh ◽  
Gas Bearings ◽  
Force Coefficients ◽  
Test Parameters ◽  
Gas Bearing

Compliant hybrid gas bearings combine key enabling features from both fixed geometry externally pressurized gas bearings and compliant foil bearings. The compliant hybrid bearing relies on both hydrostatic and hydrodynamic film pressures to generate load capacity and stiffness to the rotor system, while providing damping through integrally mounted metal mesh bearing support dampers. This paper presents experimentally identified force coefficients for a 110 mm compliantly damped gas bearing using a controlled-motion test rig. Test parameters include hydrostatic inlet pressure, excitation frequency, and rotor speed. The experiments were structured to evaluate the feasibility of implementing these bearings in large size turbomachinery. Dynamic test results indicate weak dependency of equivalent direct stiffness coefficients to most test parameters except for frequency and speed, where higher speeds and excitation frequency decreased equivalent bearing stiffness values. The bearing system equivalent direct damping was negatively impacted by increased inlet pressure and excitation frequency, while the cross-coupled force coefficients showed values an order of magnitude lower than the direct coefficients. The experiments also include orbital excitations to simulate unbalance response representative of a target machine while synchronously traversing a critical speed. The results indicate that the gas bearing can accommodate vibration levels larger than the set bore clearance while maintaining satisfactory damping levels.

Compliant Hybrid Gas Bearing Using Integral Hermetically Sealed Squeeze Film Dampers

2019 ◽  
Vol 141 (10) ◽  
Author(s):  
Bugra Ertas
Keyword(s):  
Squeeze Film ◽  
Force Coefficients ◽  
Overall Design ◽  
Single Piece ◽  
Squeeze Film Dampers ◽  
Tilting Pad ◽  
Support Force ◽  
Bearing Design ◽  
Gas Bearing ◽  
Gaining Insight

AbstractThis paper focuses on an integral gas-film lubricated bearing concept developed to enable the oil-free operation of super-critical carbon dioxide (sCO2) turbomachinery. The externally pressurized tilting pad bearing concept possesses a flexible bearing support with an integral hermetically sealed squeeze film damper. Unlike the past concepts using modular hermetic squeeze film dampers presented, the bearing design in this work utilizes advanced manufacturing methods to yield an integral single piece design in efforts to reduce space envelope, cost, and improve overall design reliability. The paper advances a detailed description of the bearing design and identification of bearing support force coefficients. Nonrotating benchtop tests show the influence of vibration amplitude, frequency, and damper cavity pressurization on force coefficients for two different viscosity fluids. Results indicate an increase in stiffness and a decrease in damping when increasing the frequency of excitation. Damper cavity pressurization was shown to eliminate squeeze film cavitation for the vibration amplitudes and frequency range in the study. Additionally, the paper advances a transient fluid–structure interaction (FSI) analysis aimed at gaining insight on the interaction of flexible elements bounding a hermetic fluid volume experiencing sinusoidal vibratory motion. The analysis considers an idealized damper model with and without a vibration transmission post while varying diaphragm modulus of elasticity for three excitation frequencies. Computational results were able to capture the increase in stiffness and the decrease in damping and show that the flexibility of the bounding elements influence the damper cavity volume change and phase ultimately affecting dynamic cavity pressures and force coefficients.

The Role of Pivot Stiffness on the Dynamic Force Coefficients of Tilting Pad Journal Bearings

2013 ◽  
Vol 135 (11) ◽  
Author(s):  
Luis San Andrés ◽  
Yujiao Tao
Keyword(s):  
Experimental Data ◽  
Journal Bearings ◽  
Fluid Film ◽  
Virtual Mass ◽  
Force Coefficients ◽  
Tilting Pad ◽  
Frequency Independent ◽  
Bearing Force ◽  
Film Stiffness ◽  
Tilting Pad Journal Bearings

Recent comprehensive experimental data showcasing the force coefficients of commercial size tilting pad journal bearings has brought to rest the long standing issue on the adequacy of the [K,C,M] physical model to represent frequency independent bearing force coefficients, in particular viscous damping. Most experimental works test tilting pad journal bearings (TPJBs) with large preloads, operating over a large wide range of rotor speeds, and with null to beyond normal specific loads. Predictions from apparently simple fluid film bearing models stand poor against the test data which invariably signals to theory missing pivot and pad flexibility effects, and most importantly, ignoring significant differences in bearing and pad clearances due to actual operation, poor installation and test procedures, or simply errors in manufacturing and assembly. Presently, a conventional thermo hydrodynamic bulk flow model for prediction of the pressure and temperature fields in TPJBs is detailed. The model accounts for various pivot stiffness types, all load dependent and best when known empirically, and allows for dissimilar pad and bearing clearances. The algorithm, reliable even for very soft pad-pivots, predicts frequency reduced bearing impedance coefficients and over a certain frequency range delivers the bearing stiffness, damping and virtual mass force coefficients. Good correlation of predictions against a number of experimental results available in the literature bridges the gap between a theoretical model and the applications. Predicted pad reaction loads reveal large pivot deflections, in particular for a bearing with large preloaded pads, with significant differences in pivot stiffness as a function of specific load and operating speed. The question on how pivot stiffness acts to increase (or decrease) the bearing force coefficients, in particular the dynamic stiffness versus frequency, remains since the various experimental data show contradictory results. A predictive study with one of the test bearings varies its pivot stiffness from 10% of the fluid film stiffness to an almost rigid one, 100 times larger. With certainty, bearings with nearly rigid pivot stiffness show frequency independent force coefficients. However, for a range of pad pivot stiffness, 1/10 to ten times the fluid film stiffness, TPJB impedances vary dramatically with frequency, in particular as the excitation frequency grows above synchronous speed. The bearing virtual mass coefficients become negative, thus stiffening the bearing for most excitation frequencies.

Assessment of Porous Type Gas Bearings: Measurements of Bearing Performance and Rotor Vibrations

2016 ◽  
Author(s):  
Luis San Andrés ◽  
Travis A. Cable ◽  
Yong Zheng ◽  
Oscar De Santiago ◽  
Drew Devitt
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Load Capacity ◽  
Gas Bearings ◽  
Rotor Spinning ◽  
Supply Pressure ◽  
Seizure Event ◽  
Flow Drag ◽  
Gas Bearing

Gas bearings are an attractive means of load support for rotating machinery due to their low mechanical power losses and dispensing of expensive lubrication systems. A subset of gas bearing technology, porous type gas bearings utilize a porous material as a means of feeding externally pressurized gas (typically air) to the bearing clearance region. When compared to typical orifice type hydrostatic bearings, porous bearings distribute pressurized gas more uniformly into the film clearance, thus resulting in a higher load capacity for similar flow rates [1]. The majority of the literature on porous type gas bearings focuses on the numerical evaluation of cylindrical bushings, yet experimental data on their performance is scant. As a follow up to Ref. [2], the paper presents an analysis of measurements of flow, drag torque and rotordynamic response of a large (100 mm OD, ∼275 N) rotor supported on two tilting pad (five-pad) porous journal bearings (specific load∼19 kPa). Measurements of air mass flow into the bearings, with and without the rotor in place, show that the film clearance offers little restriction. The mass flow rate is proportional to the supply pressure and lead to an estimated permeability coefficient. In operation with various levels of supply pressure and with the rotor spinning to 8 krpm (133 Hz, surface speed ∼42 m/s), several rotordynamic response tests (masses up to 6.9 gram) show the rotor amplitude of synchronous response is proportional to the mass imbalance; hence demonstrating the system is linear. Finally, rotor speed coast down tests from 8 krpm show that the bearings offer little drag friction; and increasing the supply pressure gives to lesser drag. The measurements verify the pair of gas bearings support effectively the rigid rotor with little expense in mass flow rate delivered to them. Most importantly, while operating at 10 krpm with a large added imbalance, the system survived a seizure event with little damage to the rotor and bearings, both restored to a near pristine condition after a simple cleaning procedure.

Thermal Wedge Lubrication of Parallel Surface Thrust Bearings

1965 ◽  
Vol 87 (4) ◽  
pp. 823-830 ◽  
Author(s):  
I. G. Currie ◽  
C. A. Brockley ◽  
F. A. Dvorak
Keyword(s):  
Thrust Bearing ◽  
Hydrodynamic Lubrication ◽  
Load Capacity ◽  
Performance Comparison ◽  
Superior Performance ◽  
Stable Operation ◽  
Parallel Surface ◽  
Tilting Pad ◽  
Performance Curves ◽  
Load Carrying

The parallel surface thrust bearing has been studied both theoretically and experimentally. The general equations governing the laminar flow of a Newtonian fluid are presented and suitably reduced to describe the flow of lubricant through a plain collar bearing with sector pads. A computer solution of the resulting equations has been obtained in which the variations of density and viscosity with temperature are accommodated and the circumferential leakage of oil from the bearing is recognized. The resulting performance curves indicate that useful load-carrying capacities, produced by a “thermal wedge” effect, are possible with a parallel surface thrust bearing. The effect of the inlet oil temperature and bearing speed on the performance is shown. Tests were carried out on three, four, and five-pad bearings operating at 15,000 rpm. It was found that circumferential oil seals were required to insure stable operation. The results confirm that hydrodynamic lubrication may be achieved with a parallel surface thrust bearing. However, it was found that some practical limitations are imposed by high temperatures. A comparison between the theoretical load capacity of an optimum tilting pad bearing and that of a parallel surface bearing for equivalent pad dimensions, speed, and lubricant conditions revealed that the tilting pad bearing had the superior performance. Comparison of friction results with the findings of other workers shows good agreement.

Stability and Unbalance Analysis of Rigid Rotors Supported by Spiral Groove Bearings: Comparison of Different Approaches

2021 ◽  
Author(s):  
Elia Iseli ◽  
Jurg Schiffmann
Keyword(s):  
Load Capacity ◽  
Critical Mass ◽  
Mode Shapes ◽  
Response Analysis ◽  
Full Time ◽  
Number Range ◽  
Force Coefficients ◽  
Unbalance Response ◽  
Bearing Force ◽  
Gas Bearing

Abstract The dynamic behavior of spiral-grooved gas bearing supported 4DoF rotors is investigated by means of linearized bearing force coefficients and full time-integrated transient analysis. The two methods are compared for a variation of test rotors and bearing geometries in a given compressibility number interval of Lambda = [0,40]. The limitations and weaknesses of the linearized model are presented. It is shown that shafts with two symmetric herringbone-groove journal bearings have their maximum stability and load capacity if the center of gravity lays in the middle of the two bearings. For symmetric rotors (la/lb = 1) the two rigid modes, cylindrical and conical, are present and are influenced by the mass and transverse moment of inertia independently. For asymmetric rotors (la/lb < 1) the stability region decreases and the modes have a mixed shape. It is no longer possible to clearly distinguish between pure cylindrical and pure conical mode shapes. The two methods predict the critical mass and critical transverse moment of inertias within a difference of < 7%. A quasi-linear unbalance module for rigid gas bearing supported rotors is presented, which considers eccentricity dependent bearing force coefficients, allowing to speed up the unbalance response analysis by four orders of magnitude. The unbalance module is compared with the full transient orbital analysis, suggesting that the quasi-linear module predicts the non-linear unbalance response with <6% deviation for amplitudes up to e < 0.5 within the complete compressibility number range.

Compliant Hybrid Gas Bearing Using Integral Hermetically-Sealed Squeeze Film Dampers

2019 ◽  
Author(s):  
Bugra Ertas
Keyword(s):  
Past Research ◽  
Squeeze Film ◽  
Force Coefficients ◽  
Overall Design ◽  
Single Piece ◽  
Squeeze Film Dampers ◽  
Tilting Pad ◽  
Support Force ◽  
Bearing Design ◽  
Gas Bearing

Abstract The following paper focuses on an integral gas-film lubricated bearing concept developed to enable the oil-free operation of super-critical carbon dioxide (sCO2) turbomachinery. The externally pressurized tilting pad bearing concept possesses a flexible bearing support with an integral hermetically sealed squeeze film damper. Unlike the initial concepts using modular hermetic squeeze film dampers presented in past research, the bearing design in this work utilizes advanced manufacturing methods to yield an integral single piece design developed to reduce space envelope, cost, and improved overall design reliability. The paper advances a detailed description of the bearing design and identification of bearing support force coefficients. Non-rotating bearing support test results show the influence of vibration amplitude, frequency, and damper cavity pressurization on force coefficients for two different viscosity fluids. Results indicate an increase in stiffness and a decrease in damping when increasing the frequency of excitation. Damper cavity pressurization was shown to eliminate squeeze film cavitation for the vibration amplitudes and frequency range in the study. Additionally, the paper advances a transient fluid-structure interaction (FSI) analysis aimed at gaining insight on the interaction of flexible elements bounding a hermetic fluid volume experiencing sinusoidal vibratory motion. The analysis considers an idealized damper model with and without a vibration transmission post while varying diaphragm modulus of elasticity for three excitation frequencies. Computational results were able to capture the increase in stiffness and decrease in damping and show that the flexibility of the bounding elements influence the damper cavity volume change and phase; ultimately effecting dynamic cavity pressures and force coefficients.

The Role of Pivot Stiffness on the Dynamic Force Coefficients of Tilting Pad Journal Bearings

2013 ◽  
Author(s):  
Luis San Andrés ◽  
Yujiao Tao
Keyword(s):  
Experimental Data ◽  
Journal Bearings ◽  
Fluid Film ◽  
Virtual Mass ◽  
Force Coefficients ◽  
Tilting Pad ◽  
Frequency Independent ◽  
Bearing Force ◽  
Film Stiffness ◽  
Tilting Pad Journal Bearings

Recent comprehensive experimental data showcasing the force coefficients of commercial size tilting pad journal bearings has brought to rest the long standing issue on the adequacy of the [K,C,M] physical model to represent frequency independent bearing force coefficients, in particular viscous damping. Most experimental works test TPJBs with large preloads, operating over a large wide range of rotor speeds, and with null to beyond normal specific loads. Predictions from apparently simple fluid film bearing models stand poor against the test data which invariably signals to theory missing pivot and pad flexibility effects, and most importantly, ignoring significant differences in bearing and pad clearances due to actual operation, poor installation and test procedures, or simply errors in manufacturing and assembly. Presently, a conventional thermo hydrodynamic bulk flow model for prediction of the pressure and temperature fields in TPJBs is detailed. The model accounts for various pivot stiffness types, all load dependent and best when known empirically, and allows for dissimilar pad and bearing clearances. The algorithm, reliable even for very soft pad-pivots, predicts frequency reduced bearing impedance coefficients and, over a certain frequency range, delivers the bearing stiffness, damping and virtual mass force coefficients. Good correlation of predictions against a number of experimental results available in the literature bridges the gap between a theoretical model and the applications. Predicted pad reaction loads reveal large pivot deflections, in particular for a bearing with large preloaded pads, with significant differences in pivot stiffness as a function of specific load and operating speed. The question on how pivot stiffness acts to increase (or decrease) the bearing force coefficients, in particular the dynamic stiffness vs. frequency, remains since the various experimental data show contradictory results. A predictive study with one of the test bearings varies its pivot stiffness from 10% of the fluid film stiffness to an almost rigid one, 100 times larger. With certainty, bearings with nearly rigid pivot stiffness show frequency independent force coefficients. However, for a range of pad pivot stiffness, 1/10 to ten times the fluid film stiffness, TPJB impedances vary dramatically with frequency, in particular as the excitation frequency grows above synchronous speed. The bearing virtual mass coefficients become negative, thus stiffening the bearing for most excitation frequencies.

Experimental Identification of Dynamic Force Coefficients for a 110 MM Compliantly Damped Hybrid Gas Bearing

2015 ◽  
Vol 137 (7) ◽  
Author(s):  
Adolfo Delgado
Keyword(s):  
Load Capacity ◽  
Excitation Frequency ◽  
Dynamic Test ◽  
Inlet Pressure ◽  
Dynamic Force ◽  
Metal Mesh ◽  
Gas Bearings ◽  
Force Coefficients ◽  
Test Parameters ◽  
Gas Bearing

Compliant hybrid gas bearings (HGBs) combine key enabling features from both fixed geometry externally pressurized gas bearings and compliant foil bearings. The compliant hybrid bearing relies on both hydrostatic and hydrodynamic film pressures to generate load capacity and stiffness to the rotor system, while providing damping through integrally mounted metal mesh bearing support dampers. This paper presents experimentally identified force coefficients for a 110 mm compliantly damped gas bearing using a controlled-motion test rig. Test parameters include hydrostatic inlet pressure, excitation frequency, and rotor speed. The experiments were structured to evaluate the feasibility of implementing these bearings in large size turbomachinery. Dynamic test results indicate weak dependency of equivalent direct stiffness coefficients to most test parameters except for frequency and speed, where higher speeds and excitation frequency decreased equivalent bearing stiffness values. The bearing system equivalent direct damping was negatively impacted by increased inlet pressure and excitation frequency, while the cross-coupled force coefficients showed values an order of magnitude lower than the direct coefficients. The experiments also include orbital excitations to simulate unbalance response representative of a target machine while synchronously traversing a critical speed. The results indicate the gas bearing can accommodate vibration levels larger than the set bore clearance while maintaining satisfactory damping levels.

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