scholarly journals Study on the temperature and strain fields in gas foil bearings – measurement method and numerical simulations

2021 ◽  
Vol 23 (3) ◽  
pp. 540-547
Author(s):  
Paweł Zdziebko ◽  
Adam Martowicz
Keyword(s):  
Gas Turbines ◽  
Measurement Method ◽  
The Finite Element Method ◽  
Strain Fields ◽  
Foil Bearings ◽  
Experimental Identification ◽  
Foil Bearing ◽  
Thermomechanical Couplings ◽  
Air Film ◽  
Mechanical Phenomena

Gas foil bearings belong to the group of slide bearings and are used in devices in which operation at high rotational speeds of the shafts are of key importance, e.g., in gas turbines. The air film developed on the surface of the bearing’s top foil allows this structural component to be separated from the shaft. This ensures a non-contact operation of the bearing. In the case of the mentioned type of bearings, their resultant operational properties are influenced by both thermal and mechanical phenomena. The current work presents a model of a gas foil bearing developed making use of the Finite Element Method. The model takes into account thermomechanical couplings which are necessary for the correct simulation of the operation of physical components of the modeled system. The paper reports the results of numerical analyzes conducted for the elaborated model as well as the relevant conclusions concerning thermomechanical couplings present in gas foil bearings. The method for the experimental identification of the temperature and strain fields in the bearing’s top foil proposed to validate the numerical model is also presented.

A Contribution to the Thermal Modeling of Bump Type Air Foil Bearings: Analysis of the Thermal Resistance of Bump Foils

2017 ◽  
Vol 139 (6) ◽  
Author(s):  
Andreas Lehn ◽  
Marcel Mahner ◽  
Bernhard Schweizer
Keyword(s):  
Thermal Resistance ◽  
Thermal Contact ◽  
Applied Pressure ◽  
Analytical Formula ◽  
Base Plate ◽  
Air Gaps ◽  
Foil Bearings ◽  
Foil Bearing ◽  
Air Film ◽  
Good Agreement

A detailed analysis of the effective thermal resistance for the bump foil of air foil bearings (AFBs) is performed. The presented model puts emphasis on the thermal contact resistances between the bump foil and the top foil as well as between the bump foil and the base plate. It is demonstrated that most of the dissipated heat in the lubricating air film of an air foil bearing is not conducted by microcontacts in the contact regions. Instead, the air gaps close to the contact area are found to be thin enough in order to effectively conduct the heat from the top foil into the bump foil. On the basis of these findings, an analytical formula is developed for the effective thermal resistance of a half bump arc. The formula accounts for the geometry of the bump foil as well as for the surface roughness of the top foil, the bump foil, and the base plate. The predictions of the presented model are shown to be in good agreement with measurements from the literature. In particular, the model predicts the effective thermal resistance to be almost independent of the applied pressure. This is a major characteristic property that has been found by measurements but could not be reproduced by previously published models. The presented formula contributes to an accurate thermohydrodynamic (THD) modeling of AFBs.

On Controlling the Film Thickness in Self-Acting Foil Bearings

1970 ◽  
Vol 92 (2) ◽  
pp. 359-362 ◽  
Author(s):  
A. Eshel
Keyword(s):  
Film Thickness ◽  
Free Path ◽  
Marked Effect ◽  
Solid Wall ◽  
Mean Free Path ◽  
Radius Of Curvature ◽  
Air Gaps ◽  
Foil Bearings ◽  
Foil Bearing ◽  
Air Film

Some factors useful in overcoming excessive air gaps in foil bearings are investigated. Since the gaps of interest are small, the foil bearing equations are modified to include the effects of the molecular mean free path. It is shown that by small corners in the solid wall, one can reduce the air film thickness considerably. A change in curvature with continuous slope has also a marked effect on the film thickness. Theoretical prediction curves allowing the calculation of the air gap as a function of corner angle, change in radius of curvature, and the molecular mean free path are presented.

Calculation of Static and Dynamic Characteristics of Multi Wounded Radial Foil Bearing Based on Leakage Flow Induced Vibration Theory

2006 ◽  
Author(s):  
Shigehiko Kaneko ◽  
Xiaoshan Wu
Keyword(s):  
Dynamic Characteristics ◽  
Gas Turbines ◽  
Dynamic Pressure ◽  
Design Guidelines ◽  
Leakage Flow ◽  
Flow Induced Vibration ◽  
Static And Dynamic Characteristics ◽  
Foil Bearings ◽  
Vibration Theory ◽  
Foil Bearing

Dynamic pressure type foil bearings are expected to serve as shaft bearings for Micro Gas Turbines (MGT). In this study, in order to establish design guidelines of radial foil bearings, dynamical modeling of multi wounded foil bearing was carried out employing leakage flow induced vibration theory. Taking frictional forces due to attached part of the foil and the protrusion, etc. into consideration, static and dynamic characteristics were analyzed to examine the performance and the stability of radial foil bearings.

Development and Testing of Air Foil Bearing System for an Automotive Exhaust Gas Turbocharger

2016 ◽  
Vol 831 ◽  
pp. 71-80 ◽  
Author(s):  
Uwe Borchert ◽  
Antonio Delgado ◽  
Janusz A. Szymczyk
Keyword(s):  
Gas Turbines ◽  
Rotation Speed ◽  
Test Facility ◽  
Exhaust Gas ◽  
Automotive Exhaust ◽  
Radial Wave ◽  
Foil Bearings ◽  
Foil Bearing ◽  
Contact Free ◽  
Bearing System

Lubricated bearings are usually used to support and guide the shafts in gas turbines, exhaust gas turbochargers and other turbomachines. The lubricant is also used for cooling the hot parts such as the turbine side of the rotor. The high temperature condition effects a contamination of the compressed air by evaporating the lubricant. In special applications an oil-free operation has to be guaranteed. In other applications an oil lubricated bearing system prevents an immediate engine stop. The use of air foil bearings eliminates the disadvantages of the oil lubricated bearings. An air foil bearing works self-adjusting the necessary gap which depends on relative speed of the rotor and the stator surfaces and on the viscosity of the lubricating fluid. A low rotor speed requires a small bearing gap, whereas the gap must be enlarged for high speed at constant viscosity of the lubricant. An air foil bearing works contact-free in a wide speed range even at small rotation speed depending on design. On an experimental basis an air foil bearing system was developed and tested for a standard automotive exhaust gas turbocharger. The developed bearings need no infrastructure for supplying with lubricant and its cooling and filtering. The air foil bearings was calculated and designed based on the estimated bearing loads. For the manufacturing of the radial wave springs a procedure was developed. A test facility was set up for the experiments. The modified rotor works at the standard rotation speed of 80000 rpm. The bearings support and guide the shaft contact-free (without wear) in a range of a few thousands of revolutions per minute up to the standard rotation speed.

Dynamic Properties Analysis of Compliant Foil Aerodynamic Bearings Based on Spring Model

2011 ◽  
Vol 86 ◽  
pp. 252-255
Author(s):  
Si Xing Liu ◽  
Xi Zhi Ma
Keyword(s):  
Dynamic Properties ◽  
Mathematic Model ◽  
Published Data ◽  
Spring Model ◽  
The Finite Element Method ◽  
Foil Bearings ◽  
Dynamic Coefficients ◽  
Foil Bearing ◽  
Critical Rotational Speed ◽  
The Stability

The dynamic coefficients are the essential parameters, which could be used to determine the critical rotational speed, an unbalance response and the stability analysis. A plural mathematic model of the coefficients calculation is developed by using the numerical perturbation method. A spring model is applied to get the foil deformation. The dynamic coefficients of the gas foil bearings are obtained through the application of the finite difference method and the finite element method. The results show that the dynamic coefficients are closely related to the journal eccentricity and whirl ratio. With the results compared to the published data, the model is proved to be accurate. And the coefficients could be used as a reference for the design of a gas foil bearing.

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.

Static Determinacy in the Theory of Finite Width Foil Bearings

1974 ◽  
Vol 41 (1) ◽  
pp. 51-54 ◽  
Author(s):  
W. E. Langlois
Keyword(s):  
Force Balance ◽  
Finite Width ◽  
Foil Bearings ◽  
Lubrication Equation ◽  
Foil Bearing ◽  
Edge Conditions ◽  
Single Force ◽  
Static Determinacy ◽  
Force Balance Equation ◽  
Determinate Problem

The assumption of “perfect flexibility” is shown to be self-consistent in an important class of finite-width foil bearing problems. When the membrane equations are written in the “stretched coordinates” of foil bearing theory, the usual edge conditions on the tape result in a statically determinate problem. The tape dynamics couples to the Reynolds lubrication equation through a single force-balance equation which does not entail the elastic strain.

Experimental Evaluation of the Structure Characterization of a Novel Hybrid Bump-Metal Mesh Foil Bearing

2015 ◽  
Vol 138 (2) ◽  
Author(s):  
Kai Feng ◽  
Yuman Liu ◽  
Xueyuan Zhao ◽  
Wanhui Liu
Keyword(s):  
Excitation Frequency ◽  
Structure Characterization ◽  
Viscous Damping ◽  
Metal Mesh ◽  
Equivalent Viscous Damping ◽  
Foil Bearings ◽  
Damping Characteristics ◽  
Foil Bearing ◽  
Mesh Density ◽  
Load Tests

Rotors supported by gas foil bearings (GFBs) experience stability problem caused by subsynchronous vibrations. To obtain a GFB with satisfactory damping characteristics, this study presented a novel hybrid bump-metal mesh foil bearing (HB-MMFB) that consists of a bump foil and metal mesh blocks in an underlying supporting structure, which takes advantage of both bump-type foil bearings (BFBs) and MMFBs. A test rig with a nonrotating shaft was designed to estimate structure characterization. Results from the static load tests show that the proposed HB-MFBs exhibit an excellent damping level compared with the BFBs with a similar size because of the countless microslips in the metal mesh blocks. In the dynamic load tests, the HB-MFB with a metal mesh density of 36% presents a viscous damping coefficient that is approximately twice that of the test BFB. The dynamics structural coefficients of HB-MFBs, including structural stiffness, equivalent viscous damping, and structural loss factor, are all dependent on excitation frequency and motion amplitude. Moreover, they exhibit an obvious decrease with the decline in metal mesh density.

Comparative Evaluation of Foil Bearings With Different Compliant Structures for Improved Manufacturability

2017 ◽  
Author(s):  
K. Shalash ◽  
J. Schiffmann
Keyword(s):  
Cantilever Beam ◽  
Static Load ◽  
Measurement Tool ◽  
Reduced Order ◽  
Foil Bearings ◽  
Compliant Structure ◽  
Foil Bearing ◽  
Local Stiffness ◽  
Beam Foil ◽  
Bearing System

Potential geometrical deviations in bump foil bearings due to manufacturing uncertainty can have significant effects on both the local stiffness and clearance, and hence, affecting the overall bearing performance. The manufacturing uncertainty of bump type foil bearings was investigated, showing large geometrical deviations, using a developed measurement tool for the formed bump foils. A reduced order foil bearing model was used in a Monte Carlo simulation studying the effect of manufacturing noise on the onset of instability, highlighting the sensitivity of the rotor-bearing system to such manufacturing deviations. It was found that 30% of the simulated cases resulted improvements in stability, the remaining cases underperformed. Attempting to increase the robustness of the bearing, two other compliant structures replacing the classical gen-II bump foils were investigated from a manufacturing perspective. The first is a modified bump type Sinusoidal foil, and the second is the Cantilever beam foil. Consequently, quasi-static load-displacement tests were executed showing deviations in local clearance and stiffness for the classical bump type compliant structure compared to the other designs. It was found that the Cantilever beam foils yield more robustness compared to the bump type foils. Finally, an analytical model for the sequential engagement of the compliant structure is presented and validated with experimental measurements for both bump type and Cantilever structures.

Rotordynamics Performance of Hybrid Foil Bearing Under Forced Vibration Input

2017 ◽  
Author(s):  
Daejong Kim ◽  
Brian Nicholson ◽  
Lewis Rosado ◽  
Garry Givan
Keyword(s):  
Impulse Response ◽  
High Speed ◽  
Load Capacity ◽  
Supply System ◽  
Forced Response ◽  
Experimental Results ◽  
Lateral Acceleration ◽  
Foil Bearings ◽  
Foil Bearing ◽  
Gas Supply

Foil bearings are one type of hydrodynamic air/gas bearings but with a compliant bearing surface supported by structural material that provides stiffness and damping to the bearing. The hybrid foil bearing (HFB) in this paper is a combination of a traditional hydrodynamic foil bearing with externally-pressurized air/gas supply system to enhance load capacity during the start and to improve thermal stability of the bearing. The HFB is more suitable for relatively large and heavy rotors where rotor weight is comparable to the load capacity of the bearing at full speed and extra air/gas supply system is not a major added cost. With 4,448N∼22,240N thrust class turbine aircraft engines in mind, the test rotor is supported by HFB in one end and duplex rolling element bearings in the other end. This paper presents experimental work on HFB with diameter of 102mm performed at the US Air force Research Laboratory. Experimental works include: measurement of impulse response of the bearing to the external load corresponding to rotor’s lateral acceleration of 5.55g, forced response to external subsynchronous excitation, and high speed imbalance response. A non-linear rotordynamic simulation model was also applied to predict the impulse response and forced subsynchronous response. The simulation results agree well with experimental results. Based on the experimental results and subsequent simulations, an improved HFB design is also suggested for higher impulse load capability up to 10g and rotordynamics stability up to 30,000rpm under subsynchronous excitation.

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