Design Space of Foil Bearings for Closed-Loop Supercritical CO2 Power Cycles Based on Three-Dimensional Thermohydrodynamic Analyses

2015 ◽  
Vol 138 (3) ◽  
Author(s):  
Daejong Kim
Keyword(s):  
Power Loss ◽  
Closed Loop ◽  
Ambient Pressure ◽  
Three Dimensional ◽  
Measured Data ◽  
Analysis Tool ◽  
Power Cycles ◽  
Foil Bearings ◽  
Foil Bearing ◽  
Flow Turbulence

The closed-loop Brayton cycle with supercritical CO2 (S-CO2) as an operating fluid is an attractive alternative to conventional power cycles due to very high power density. Foil gas bearings using CO2 are the most promising for small S-CO2 turbomachinery but there are many problems to address: large power loss due to high flow turbulence, lack of design/analysis tool due to nonideal gas behavior, and lack of load capacity when they are used for large systems. This paper presents high-level design/analysis tool involving three-dimensional (3D) thermohydrodynamic (THD) analyses of radial foil bearings considering real gas effect and flow turbulence inside the film. Simulations are performed for radial foil bearing with 34.9 mm in diameter and lubricated with CO2 and N2 under various ambient conditions up to above 40 bar gauge pressure. The simulation results using the turbulence model still underpredict the measured data in open literature. However, the error between the prediction and measurements decreases as either speed or ambient pressure increases. In addition, general behavior of substantial increase in power loss with ambient pressure agrees with the measured data. The simulation results indicate the importance of detailed THD analysis of the foil bearings for prediction of power loss under severe turbulent condition. A conceptual layout of rotor system for 10 MWe S-CO2 loop is also presented along with realistic rotor weight and bearing load. A hybrid foil bearing with diameter of 102 mm is suggested for gas generator rotor, and its power losses and minimum film thicknesses at various operating conditions are presented.

Design Space of Foil Bearings for Closed Loop Supercritical CO2 Power Cycles Based on Three-Dimensional Thermo-Hydrodynamic Analyses

2015 ◽  
Author(s):  
Daejong Kim
Keyword(s):  
Power Loss ◽  
Closed Loop ◽  
Ambient Pressure ◽  
Three Dimensional ◽  
Measured Data ◽  
Analysis Tool ◽  
Power Cycles ◽  
Foil Bearings ◽  
Flow Turbulence ◽  
Simulation Results

The closed loop Brayton cycle with super critical CO2 (S-CO2) as an operating fluid is an attractive alternative to conventional power cycles due to very high power density. Foil gas bearings using CO2 is the most promising for small S-CO2 turbomachinery but there are many problems to address; large power loss due to high flow turbulence, lack of design/analysis tool due to non-ideal gas behavior, and lack of load capacity when they are used for large systems. This paper presents high level design/analysis tool involving three-dimensional thermo-hydrodynamic analyses of radial foil bearings considering real gas effect and flow turbulence inside the film. Simulations are performed for radial foil bearing with 34.9mm in diameter lubricated with CO2 and N2 under various ambient conditions up to above 40 bar gauge pressure. The simulation results using the turbulence model still under-predict the measured data in open literature. However, the error between the prediction and measurements decreases as either speed or ambient pressure increases. In addition, general behavior of substantial increase in power loss with ambient pressure agrees with the measured data. The simulation results indicate the importance of detailed THD analysis of the foil bearings for prediction of power loss under severe turbulent condition. A conceptual layout of rotor system for 10MWe S-CO2 loop is also presented along with realistic rotor weight and bearing load. A hybrid foil bearings with diameter of 102mm is suggested for gas generator rotor, and its power losses and minimum film thicknesses at various operating conditions are presented.

Three-Dimensional Turbulent Thermo-Elastohydrodynamic Analyses of Hybrid Thrust Foil Bearings Using Real Gas Model

2016 ◽  
Author(s):  
Fangcheng Xu ◽  
Daejong Kim
Keyword(s):  
Power Generation ◽  
Power Loss ◽  
Closed Loop ◽  
Load Capacity ◽  
Three Dimensional ◽  
Analysis Tool ◽  
Real Gas ◽  
Gas Bearings ◽  
Foil Bearings ◽  
Flow Turbulence

Environment-friendly power generation systems are active area of research. Among many systems, closed loop Brayton cycles using super critical CO2 (S-CO2) is attractive alternative to conventional power cycles due to very high efficiency and power density. When converting low temperature thermal energy such as waste heat to electrical power, closed loop organic Rankine cycles (ORC) using refrigerants are very popular. Large utility scale systems adopting S-CO2 or ORC cycles require traditional bearing systems with dry gas seals, but small systems with shaft power less than 1MW are best suited with gas bearings lubricated with the cycle fluids. Foil gas bearings, which have been successfully applied to the air blowers/compressors and small power generation gas turbines, are the best candidate for the small S-CO2 or ORC cycle systems. However, design/analysis tool of the foil bearings with these non-ideal gases is rare. In addition, thrust foil bearings are technically more challenging compared to radial foil bearings due to low load capacity and large power loss due to high flow turbulence. This paper presents high level analysis tool involving three-dimensional thermo-hydrodynamic analyses of hybrid thrust foil bearings employing real gas effect and flow turbulence inside the film. The pressure distribution, temperature distribution, load capacity, film thickness, and power loss of 154mm hybrid thrust foil bearings are presented.

scholarly journals A New Analysis Tool Assessment for Rotordynamic Modeling of Gas Foil Bearings

2010 ◽  
Author(s):  
Samuel A. Howard ◽  
Luis San Andre´s
Keyword(s):  
Power Loss ◽  
High Speed ◽  
Structural Deformation ◽  
Analysis Tool ◽  
Test Rig ◽  
Contributing Factors ◽  
Foil Bearings ◽  
Rotordynamic Coefficients ◽  
Foil Bearing ◽  
Analytical Tools

Gas foil bearings offer several advantages over traditional bearing types that make them attractive for use in high-speed turbomachinery. They can operate at very high temperatures, require no lubrication supply (oil pumps, seals, etc), exhibit very long life with no maintenance, and once operating airborne, have very low power loss. The use of gas foil bearings in high-speed turbomachinery has been accelerating in recent years, although the pace has been slow. One of the contributing factors to the slow growth has been a lack of analysis tools, benchmarked to measurements, to predict gas foil bearing behavior in rotating machinery. To address this shortcoming, NASA Glenn Research Center (GRC) has supported the development of analytical tools to predict gas foil bearing performance. One of the codes has the capability to predict rotordynamic coefficients, power loss, film thickness, structural deformation, and more. The current paper presents an assessment of the predictive capability of the code, named XLGFBTH©. A test rig at GRC is used as a simulated case study to compare rotordynamic analysis using output from the code to actual rotor response as measured in the test rig. The test rig rotor is supported on two gas foil journal bearings manufactured at GRC, with all pertinent geometry disclosed. The resulting comparison shows that the rotordynamic coefficients calculated using XLGFBTH© represent the dynamics of the system reasonably well, especially as they pertain to predicting critical speeds.

scholarly journals A New Analysis Tool Assessment for Rotordynamic Modeling of Gas Foil Bearings

2010 ◽  
Vol 133 (2) ◽  
Author(s):  
Samuel A. Howard ◽  
Luis San Andrés
Keyword(s):  
Power Loss ◽  
High Speed ◽  
Structural Deformation ◽  
Analysis Tool ◽  
Test Rig ◽  
Contributing Factors ◽  
Foil Bearings ◽  
Rotordynamic Coefficients ◽  
Foil Bearing ◽  
Analytical Tools

Gas foil bearings offer several advantages over traditional bearing types that make them attractive for use in high-speed turbomachinery. They can operate at very high temperatures, require no lubrication supply (oil pumps, seals, etc.), exhibit very long life with no maintenance, and once operating airborne, have very low power loss. The use of gas foil bearings in high-speed turbomachinery has been accelerating in recent years although the pace has been slow. One of the contributing factors to the slow growth has been a lack of analysis tools, benchmarked to measurements, to predict gas foil bearing behavior in rotating machinery. To address this shortcoming, NASA Glenn Research Center (GRC) has supported the development of analytical tools to predict gas foil bearing performance. One of the codes has the capability to predict rotordynamic coefficients, power loss, film thickness, structural deformation, and more. The current paper presents an assessment of the predictive capability of the code named XLGFBTH©. A test rig at GRC is used as a simulated case study to compare rotordynamic analysis using output from the code to actual rotor response as measured in the test rig. The test rig rotor is supported on two gas foil journal bearings manufactured at GRC with all pertinent geometry disclosed. The resulting comparison shows that the rotordynamic coefficients calculated using XLGFBTH© represent the dynamics of the system reasonably well especially as they pertain to predicting critical speeds.

scholarly journals Compliant Foil Journal Bearing Performance at Alternate Pressures and Temperatures

2008 ◽  
Author(s):  
Robert J. Bruckner ◽  
Bernadette J. Puleo
Keyword(s):  
Journal Bearing ◽  
Load Capacity ◽  
Ambient Pressure ◽  
Operating Conditions ◽  
Test Program ◽  
Foil Bearings ◽  
Current Test ◽  
Foil Bearing ◽  
Development Risk ◽  
Highly Loaded

An experimental test program has been conducted to determine the highly loaded performance of current generation gas foil bearings at alternate pressures and temperature. Typically foil bearing performance has been reported at temperatures relevant to turbomachinery applications but only at an ambient pressure of one atmosphere. This dearth of data at alternate pressures has motivated the current test program. Two facilities were used in the test program, the ambient pressure rig and the high pressure rig. The test program utilized a 35 mm diameter by 27 mm long foil journal bearing having an uncoated Inconel X-750 top foil running against a shaft with a PS304 coated journal. Load capacity tests were conducted at 3, 6, 9, 12, 15, 18, and 21 krpm at temperatures from 25°C to 500°C and at pressures from 0.1 to 2.5 atmospheres. Results show an increase in load capacity with increased ambient pressure and a reduction in load capacity with increased ambient temperature. Below one-half atmosphere of ambient pressure a dramatic loss of load capacity is experienced. Additional lightly loaded foil bearing performance in nitrogen at 25°C and up to 48 atmospheres of ambient pressure has also been reported. In the lightly loaded region of operation the power loss increases for increasing pressure at a fixed load. Knowledge of foil bearing performance at operating conditions found within potential machine applications will reduce program development risk of future foil bearing supported turbomachines.

Influence of Ambient Pressure on Measured Stiffness and Damping of Radial Gas Foil Bearings

2021 ◽  
Author(s):  
Jason Wilkes ◽  
Steve White
Keyword(s):  
Ambient Pressure ◽  
Slight Reduction ◽  
Ambient Conditions ◽  
Diverse Range ◽  
Test Fixture ◽  
Gas Bearings ◽  
Foil Bearings ◽  
Foil Bearing ◽  
Test Loop ◽  
Analytical Tools

Abstract As gas bearings have gained popularity, they have been used in a diverse range of applications. In many cases these bearings are used in various process gases at a range of pressures. Although numerous analytical tools exist to predict the behavior of gas bearings in these environments, these tools are challenging to validate. The current work describes a test loop that is capable of measuring rotordynamic force coefficients in a hermetically sealed environment. To the author’s knowledge, this capability is the first of its kind. To illustrate operation of the test rig, an industrial 3-lobe gas-foil bearing was installed in the test fixture, and operated at pressures from .5–3.5 bara at speeds ranging from 25–65 krpm. The tests show that dynamic coefficients increase with speed and pressure; however, a slight reduction in coefficients were observed at the highest speed under ambient conditions. In addition, sub ambient pressure tests showed higher than ambient stiffness, but comparably low damping in comparison to the other test cases. It is believed that this is the first publication of gas foil bearing coefficients at sub-ambient pressure.

scholarly journals High Pressure Performance of Foil Journal Bearings in Various Gases

2008 ◽  
Author(s):  
Maxwell H. Briggs ◽  
Joseph M. Prahl ◽  
Robert Bruckner ◽  
Brian Dykas
Keyword(s):  
Carbon Dioxide ◽  
High Pressure ◽  
Atmospheric Pressure ◽  
Power Loss ◽  
Journal Bearing ◽  
Brayton Cycle ◽  
Foil Bearings ◽  
Foil Bearing ◽  
Peak Pressures

Foil bearings offer several advantages over traditional oil-lubricated bearings in closed Brayton Cycle (CBC) systems, such as those proposed for long-term space power generation. Proposed CBCs require foil bearings to use an inert gas lubricant at pressures as high as 3.0 MPa as the bearing lubricant. The High Pressure Rig (HPR) at the NASA Glenn Research Center is used to measure foil bearing power loss using potential CBC working fluids at and beyond proposed CBC peak pressures. In the current study foil journal bearing power loss is measured in helium, nitrogen, and carbon dioxide from atmospheric pressure to 4.83 MPa and at shaft speeds from 10 krpm to 42 krpm. Bearings operating in helium show no increase in power loss with increasing pressure for the conditions tested. Bearings operating in nitrogen show increases in power loss with increasing pressure at speeds above 19 krpm, while increases in bearing power loss during carbon dioxide testing were seen at 15 krpm. At speeds above these thresholds, power loss is shown to increase more rapidly in carbon dioxide than in nitrogen. Results suggest that bearing power loss performance is dependent on both gas density and shaft speed.

Effect of Foil Geometry on the Static Performance of Thrust Foil Bearings

2018 ◽  
Vol 140 (8) ◽  
Author(s):  
Gen Fu ◽  
Alexandrina Untaroiu ◽  
Erik Swanson
Keyword(s):  
Film Thickness ◽  
Load Capacity ◽  
Optimization Technique ◽  
Three Dimensional ◽  
Leading Edge ◽  
Numerical Approach ◽  
Sensitivity Study ◽  
Rotating Speed ◽  
Foil Bearings ◽  
Foil Bearing

Gas foil bearings can operate in extreme conditions such as high temperature and high rotating speed, compared to traditional bearings. They also provide better damping and stability characteristics and have larger tolerance to debris and rotor misalignment. Gas foil bearings have been successfully applied to micro- and small-sized turbomachinery, such as microgas turbine and cryogenic turbo expander. In the last decades, a lot of theoretical and experimental work has been conducted to investigate the properties of gas foil bearings. However, very little work has been done to study the influence of the foil bearing pad configuration. This study proposes a robust approach to analyze the effect of the foil geometry on the performance of a six-pad thrust foil bearing. In this study, a three-dimensional (3D) computational fluid dynamics (CFD) model for a parallel six-pad thrust foil bearing is created. In order to predict the thermal property, the total energy with viscous dissipation is used. Based on this model, the geometry of the thrust foil bearing is parameterized and analyzed using the design of experiments (DOE) methodology. In this paper, the selected geometry parameters of the foil structure include minimum film thickness, inlet film thickness, the ramp extent on the inner circle, the ramp extent on the outer circle, the arc extent of the pad, and the orientation of the leading edge. The objectives in the sensitivity study are load capacity and maximal temperature. An optimal foil geometry is derived based on the results of the DOE process by using a goal-driven optimization technique to maximize the load capacity and minimize the maximal temperature. The results show that the geometry of the foil structure is a key factor for foil bearing performance. The numerical approach proposed in this study is expected to be useful from the thrust foil bearing design perspective.

Development of a Computational Tool to Simulate Foil Bearings for Supercritical CO2 Cycles

2016 ◽  
Vol 138 (9) ◽  
Author(s):  
Kan Qin ◽  
Ingo Jahn ◽  
Rowan Gollan ◽  
Peter Jacobs
Keyword(s):  
Turbulent Flow ◽  
Supercritical Co2 ◽  
Three Dimensional ◽  
Structural Deformation ◽  
Working Fluid ◽  
Computational Tool ◽  
Element Analysis ◽  
Thrust Bearings ◽  
Foil Bearings ◽  
Foil Bearing

The foil bearing is an enabling technology for turbomachinery systems, which has the potential to enable cost efficient supercritical CO2 cycles. The direct use of the cycle's working fluid within the bearings results in an oil-free and compact turbomachinery system; however, these bearings will significantly influence the performance of the whole cycle and must be carefully studied. Moreover, using CO2 as the operating fluid for a foil bearing creates new modeling challenges. These include highly turbulent flow within the film, non-negligible inertia forces, high windage losses, and nonideal gas behavior. Since the flow phenomena within foil bearings is complex, involving coupled fluid flow and structural deformation, use of the conventional Reynolds equation to predict the performance of foil bearings might not be adequate. To address these modeling issues, a three-dimensional flow and structure simulation tool has been developed to better predict the performance of foil bearings for the supercritical CO2 cycle. In this study, the gas dynamics code, eilmer, has been extended for multiphysics simulation by implementing a moving grid framework, in order to study the elastohydrodynamic performance of foil bearings. The code was then validated for representative laminar and turbulent flow cases, and good agreement was found between the new code and analytical solutions or experiment results. A separate finite difference code based on the Kirchoff plate equation for the circular thin plate was developed in Python to solve the structural deformation within foil thrust bearings, and verified with the finite element analysis from ansys. The fluid-structure coupling algorithm was then proposed and validated against experimental results of a foil thrust bearing that used air as operating fluid. Finally, the new computational tool set is applied to the modeling of foil thrust bearings with CO2 as the operating fluid.

Parameterization of Three-Dimensional Rigid Body Guidance Incorporating Planar Gear Connections in a Spatial Closed-Loop Mechanism With Parallel Consecutive Axes

2008 ◽  
Author(s):  
Javier Rolda´n Mckinley ◽  
Carl Crane ◽  
David B. Dooner
Keyword(s):  
Computer Animation ◽  
Closed Loop ◽  
Three Dimensional ◽  
Motion Generation ◽  
Repetitive Motion ◽  
End Effector ◽  
Spatial Mechanism ◽  
Joint Axis ◽  
Position And Orientation ◽  
Six Degree Of Freedom

This paper introduces a reconfigurable closed-loop spatial mechanism that can be applied to repetitive motion tasks. The concept is to incorporate five pairs of non-circular gears into a six degree-of–freedom closed-loop spatial chain. The gear pairs are designed based on given mechanism parameters and a user defined motion specification of a coupler link of the mechanism. It is shown in the paper that planar gear pairs can be used if the spatial closed-loop chain is comprised of six pairs of parallel joint axes, i.e. the first joint axis is parallel to the second, the third is parallel to the fourth, ..., and the eleventh is parallel to the twelfth. This paper presents the synthesis of the gear pairs that satisfy a specified three-dimensional position and orientation need. Numerical approximations were used in the synthesis the non-circular gear pairs by introducing an auxiliary monotonic parameter associated to each end-effector position to parameterize the motion needs. The findings are supported by a computer animation. No previous known literature incorporates planar non-circular gears to fulfill spatial motion generation needs.

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