Experimental Identification of Force Coefficients of Large Hybrid Air Foil Bearings

2013 ◽  
Vol 136 (3) ◽  
Author(s):  
Yu Ping Wang ◽  
Daejong Kim
Keyword(s):  
Frequency Domain ◽  
Linear Perturbation ◽  
Frequency Domain Method ◽  
Impulse Responses ◽  
Significant Progress ◽  
Rotating Shaft ◽  
Foil Bearings ◽  
Stiffness Coefficients ◽  
Foil Bearing ◽  
Reliability Performance

Foil bearing technology using air or gas as a lubricant has been around since the mid-1960s, and it made significant progress in its reliability, performance, and applications. Even if significant progress has been made to the technology, the commercial applications to relatively large machines with journal shaft diameter bigger than 100 mm was not reported. This paper presents dynamic characteristics of a hybrid (hydrodynamic + hydrostatic) air foil bearing (HAFB) with a diameter of 101.6 mm and a length of 82.6 mm. The test rig configuration in this work is a floating HAFB on a rotating shaft driven by electric motor, and the HAFB is under external load. HAFB stiffness coefficients were measured using both (1) time-domain quasi-static load-deflection curves and (2) frequency-domain impulse responses, and HAFB damping coefficients were measured using only impulse responses. The HAFB direct stiffness coefficients measured from both methods are close to each other in the range of 4∼7 MN/m depending on speed, load, and supply pressure, but frequency domain method shows larger scatter in the identified coefficients. HAFB coefficients simulated with the linear perturbation method using a bump stiffness matched to the load-deflection characteristics at 18,000 rpm show reasonably good agreements with experimentally measured values.

Experimental Identification of Force Coefficients of Large Hybrid Air Foil Bearings

2013 ◽  
Author(s):  
Yu Ping Wang ◽  
Daejong Kim
Keyword(s):  
Frequency Domain ◽  
Linear Perturbation ◽  
Frequency Domain Method ◽  
Impulse Responses ◽  
Significant Progress ◽  
Rotating Shaft ◽  
Foil Bearings ◽  
Stiffness Coefficients ◽  
Foil Bearing ◽  
Reliability Performance

Foil bearing technology using air or gas as a lubricant has been around since the mid 60’s, and it made significant progress in its reliability, performance, and applications. Even if significant progress has been made to the technology, their commercial applications to relatively large machines with journal shaft diameter bigger than 100mm was not reported. This paper presents dynamic characteristics of hybrid (hydrodynamic + hydrostatic) air foil bearing (HAFB) with diameter of 101.6mm and length of 82.6mm. The test rig configuration in this work is a floating HAFB on a rotating shaft driven by electric motor, and the HAFB is under external load. HAFB stiffness coefficients were measured using both 1) time-domain quasi-static load-deflection curves, and 2) frequency-domain impulse responses, and HAFB damping coefficients were measured using only impulse responses. The HAFB direct stiffness coefficients measured from both methods are close to each other in the range of 4∼7 MN/m depending on speed, load, and supply pressure, but frequency domain method shows larger scatter in the identified coefficients. HAFB coefficients simulated with linear perturbation method using a bump stiffness matched to the load-deflection characteristics at 18,000rpm show reasonably good agreements with experimentally measured values.

Experimental Determination of Squeeze-Film Dynamic Coefficients by a Frequency Domain Method

1988 ◽  
Vol 202 (4) ◽  
pp. 235-244
Author(s):  
J B Roberts ◽  
M D Ramli ◽  
J Ellis
Keyword(s):  
Frequency Domain ◽  
Forced Vibration ◽  
Squeeze Film ◽  
Frequency Domain Method ◽  
Least Squares Regression ◽  
Stiffness Coefficients ◽  
Vibration Technique ◽  
Fluid Damping ◽  
Vibration Tests

A frequency domain, forced vibration technique for obtaining estimates of the direct fluid damping, inertial and stiffness coefficients of a squeeze-film bearing is presented. The three coefficients are estimated through a linear, least-squares regression analysis performed on data obtained from a sequence of forced vibration tests, conducted using single sinusoids of differing frequencies. The method is applied to experimental data obtained from a squeeze-film damper with a central circumferential groove and no end seals. In addition to accurate estimates of damping coefficients, reliable estimates of inertial and stiffness coefficients are obtained.

Evaluation of Foil Bearing Performance and Nonlinear Rotordynamics of 120kW Oil-Free Gas Turbine Generator

2013 ◽  
Author(s):  
Daejong Kim ◽  
An Sung Lee ◽  
Bum Seog Choi
Keyword(s):  
Frequency Domain ◽  
Gas Turbine ◽  
Turbine Rotor ◽  
Gas Generator ◽  
Turbine Generator ◽  
Element Analysis ◽  
Foil Bearings ◽  
Foil Bearing ◽  
Nonlinear Transient ◽  
Stiffness And Damping

This paper presents design approach of air foil bearings (AFBs) for 120kWe gas turbine generator, which is a single spool configuration with gas generator turbine and alternator rotor connected by a diaphragm coupling. Total four radial AFBs support the two rotors, and one set of double acting thrust foil bearing is located inside the gas generator turbine. The rotor configuration results in eight degree of freedom (DOF) rotordynamic motions, which are two cylindrical modes and two conical modes from the two rotors. Stiffness of bump foils of candidate AFB was estimated from measured structural stiffness of the bearing, and implemented to computational model for linear stiffness and damping coefficients of the bearing and frequency-domain modal impedances for cylindrical and conical modes. Stiffness of the diaphragm coupling was evaluated using finite element analysis and implemented to non-linear rotordynamic analyses of entire engine. Analyses show conical mode of turbine rotor is the main source of instability of entire engine when AFB clearance is not selected properly. Optimum AFB clearance is suggested from frequency domain modal analyses and nonlinear transient analyses.

scholarly journals Pressure Profile Measurements Within the Gas Film of Journal Foil Bearings Using an Instrumented Rotor With Telemetry

2020 ◽  
Vol 142 (3) ◽  
Author(s):  
Karim Shalash ◽  
Jürg Schiffmann
Keyword(s):  
Frequency Domain ◽  
Journal Bearing ◽  
Pressure Profile ◽  
Foil Bearings ◽  
Foil Bearing ◽  
Pressure Profiles ◽  
Fundamental Understanding ◽  
The Rich ◽  
Bearing Behavior ◽  
Circumferential Pressure

Abstract Foil bearings are strong candidates to support oil-free turbomachinery. Although foil bearings are a widely used technology, models describing their behavior are not validated using the film pressure, which is the fundamental variable of any fluid film bearing. This paper presents pressure profiles measured within the gas film of a journal foil bearing. The pressure is measured using an instrumented rotor with embedded pressure probes and wireless telemetry. The measurements yield the simultaneous circumferential pressure profiles at two axial positions inside the bearing. Proximity probes on the bearing allowed the measurement of the corresponding rotor orbits. The bearing under investigation is a bump-type compliant journal bearing, with a nominal diameter of 40 mm, an L/D = 1, and was tested up to 37.5 krpm. Load-displacement and break-away tests were performed on the test bearing in order to identify bearing parameters necessary for reproducibility. The pressure profiles are compared to a frequency domain foil bearing model. This paper is a step toward further fundamental understanding of the foil bearing behavior and the validation of the rich modeling literature.

Evaluation of Foil Bearing Performance and Nonlinear Rotordynamics of 120 kW Oil-Free Gas Turbine Generator

2013 ◽  
Vol 136 (3) ◽  
Author(s):  
Daejong Kim ◽  
An Sung Lee ◽  
Bum Seog Choi
Keyword(s):  
Frequency Domain ◽  
Gas Turbine ◽  
Turbine Rotor ◽  
Gas Generator ◽  
Turbine Generator ◽  
Element Analysis ◽  
Foil Bearings ◽  
Foil Bearing ◽  
Nonlinear Transient ◽  
Stiffness And Damping

This paper presents a design approach of air foil bearings (AFBs) for a 120 kWe gas turbine generator, which is a single spool configuration with gas generator turbine and alternator rotor connected by a diaphragm coupling. A total of four radial AFBs support the two rotors, and one set of double acting thrust foil bearing is located inside the gas generator turbine. The rotor configuration results in eight degree of freedom (DOF) rotordynamic motions, which are two cylindrical modes and two conical modes from the two rotors. Stiffness of bump foils of candidate AFB was estimated from measured structural stiffness of the bearing, and implemented to the computational model for linear stiffness and damping coefficients of the bearing and frequency-domain modal impedances for cylindrical and conical modes. Stiffness of the diaphragm coupling was evaluated using finite element analysis and implemented to nonlinear rotordynamic analyses of the entire engine. Analyses show the conical mode of the turbine rotor is the main source of instability of the entire engine when AFB clearance is not selected properly. Optimum AFB clearance is suggested from frequency domain modal analyses and nonlinear transient analyses.

scholarly journals Pressure Profile Measurements Within the Gas Film of Journal Foil Bearings Using an Instrumented Rotor With Telemetry

2019 ◽  
Author(s):  
K. Shalash ◽  
J. Schiffmann
Keyword(s):  
Frequency Domain ◽  
Journal Bearing ◽  
Pressure Profile ◽  
Foil Bearings ◽  
Foil Bearing ◽  
Pressure Profiles ◽  
Fundamental Understanding ◽  
The Rich ◽  
Bearing Behavior ◽  
Circumferential Pressure

Abstract Foil bearings are strong candidates to support oil-free turbomachinery. Although foil bearings are a widely used technology, models describing their behavior are not validated using the film pressure, which is the fundamental variable of any fluid film bearing. This paper presents pressure profiles measured within the gas film of a journal foil bearing. The pressure is measured using an instrumented rotor with embedded pressure probes and wireless telemetry. The measurements yield the simultaneous circumferential pressure profiles at two axial positions inside the bearing. Proximity probes on the bearing allowed the measurement of the corresponding rotor orbits. The bearing under investigation is a bump type compliant journal bearing, with a nominal diameter of 40mm, an L/D = 1, and was tested up to 37.5 krpm. Load-displacement and break-away tests were performed on the test bearing in order to identify bearing parameters necessary for reproducibility. The pressure profiles are compared to a frequency domain foil bearing model. This paper is a step towards further fundamental understanding of the foil bearing behavior, and the validation of the rich modelling literature.

Design of Three-Pad Hybrid Air Foil Bearing and Experimental Investigation on Static Performance at Zero Running Speed

2010 ◽  
Vol 132 (12) ◽  
Author(s):  
Daejong Kim ◽  
Donghyun Lee
Keyword(s):  
Parametric Design ◽  
Load Capacity ◽  
Hydrodynamic Pressure ◽  
Preliminary Test ◽  
Linear Perturbation ◽  
Static Stiffness ◽  
Running Speed ◽  
Foil Bearings ◽  
Foil Bearing ◽  
Static Performance

Air foil bearings (AFBs) have been explored for various micro- to midsized turbomachinery for decades, and many successful applications of the AFBs to small turbomachinery were also reported. As machine size increases, however, one of the critical technical challenges of AFBs is a wear on the top foil and rotor during starts/stops due to relatively heavy rotor weight compared with the size of the bearing. The wear on the foil increases with greater loading during starts/stops as a function of the coating performance. The hybrid air foil bearing (HAFB), which combines hydrodynamic pressure with hydrostatic lift, can help to minimize/eliminate the wear problem during the start/stops. This paper reports design and preliminary test results of hydrodynamically preloaded three-pad HAFB aimed for midsized airborne turbomachinery applications. Designed HAFB was manufactured and comprehensive parametric design simulations were performed using time-domain orbit simulations and frequency-domain linear perturbation analyses to predict performances of manufactured bearing. Static stiffness was measured at zero running speed to investigate the load capacity of hydrostatic operation when rotor is at stationary. The measured static stiffness showed good agreement with predictions.

Foil Gas Bearing With Compression Springs: Analyses and Experiments

2007 ◽  
Vol 129 (3) ◽  
pp. 628-639 ◽  
Author(s):  
Ju-ho Song ◽  
Daejong Kim
Keyword(s):  
Loss Factor ◽  
Load Capacity ◽  
Underlying Structure ◽  
Equivalent Viscous Damping ◽  
Foil Bearings ◽  
Foil Bearing ◽  
Different Types ◽  
Structural Loss ◽  
Compression Springs ◽  
Gas Bearing

A new foil gas bearing with spring bumps was constructed, analyzed, and tested. The new foil gas bearing uses a series of compression springs as compliant underlying structures instead of corrugated bump foils. Experiments on the stiffness of the spring bumps show an excellent agreement with an analytical model developed for the spring bumps. Load capacity, structural stiffness, and equivalent viscous damping (and structural loss factor) were measured to demonstrate the feasibility of the new foil bearing. Orbit and coast-down simulations using the calculated stiffness and measured structural loss factor indicate that the damping of underlying structure can suppress the maximum peak at the critical speed very effectively but not the onset of hydrodynamic rotor-bearing instability. However, the damping plays an important role in suppressing the subsynchronous vibrations under limit cycles. The observation is believed to be true with any air foil bearings with different types of elastic foundations.

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