Effect of Static Load on Critical Speeds of a Shaft Supported by Two Symmetrically Arranged Bump-Foil Bearings in a Turbocharger

2021 ◽  
pp. 279-291
Author(s):  
Minh-Quan Nguyen ◽  
Minh-Hai Pham ◽  
Van-Phong Dinh
Keyword(s):  
Static Load ◽  
Critical Speeds ◽  
Foil Bearings

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.

Effects of Mesh Density on Static Load Performance of Metal Mesh Gas Foil Bearings

2011 ◽  
Author(s):  
Yong-Bok Lee ◽  
Chang Ho Kim ◽  
Tae Ho Kim ◽  
Tae Young Kim
Keyword(s):  
Test Data ◽  
Loss Factor ◽  
Static Load ◽  
Stiffness Coefficient ◽  
Metal Mesh ◽  
Rotor Spinning ◽  
Foil Bearings ◽  
Mesh Density ◽  
Damping Loss Factor ◽  
Mesh Structures

Metal mesh materials have been used successfully in vibration isolators and bearing dampers due to their superior friction or hysteresis damping mechanism. These materials are formed to metal mesh (or wire mesh) structures in ring-shape by compressing a weave of metal wires, in general. Recently, oil-free rotating machinery implement metal mesh structures into hydrodynamic gas foil bearings by replacing bump strip layers with them, to increase its bearing structural damping. A metal mesh foil bearing (MMFB) consists of a top foil and support elastic metal mesh pads installed between a rotating shaft and a housing. The present research presents load capacity tests of a MMFB at rotor rest (0 rpm) and 30 krpm for three metal mesh densities of 13.1%, 23.2%, and 31.6%. The metal mesh pad of test MMFB is made using a stainless steel wire with a diameter of 0.15 mm. Test rig comprises a rigid rotor with a diameter of 60 mm supported on two ball bearings at both ends and test MMFB with an axial length of 50 mm floats on the rotor. Static loads is provided with a mechanical loading device on test MMFB and a strain gauge type load cell measures the applied static loads. A series of static load versus deflection tests were conducted for selected metal mesh densities at rest (0 rpm). Test data are compared to further test results of static load versus journal eccentricity recorded at the rotor speed of 30 krpm. Test data show a strong nonlinearity of bearing deflection (journal eccentricity) with static load, independent of rotor spinning. Observed hysteresis loops imply significant structural damping of test MMFB. Measured journal deflections at 0 rpm are in similar trend to recorded journal eccentricities at the finite rotor speed, thus implying that the MMFB performance depends mainly on the metal mesh structures. The paper also estimates linearlized stiffness coefficient and damping loss factor of test MMFB using the measured static load versus deflection test data at 0 rpm and 30 krpm. The results show that the highest mesh density of 31.6% produces highest linearlized stiffness coefficient and damping loss factor. With rotor spinning at 30 krpm, the linearlized stiffness coefficient and damping loss factor decrease slightly, independent of metal mesh densities. The present test data will serve as a database for benchmarking MMFB predictive models.

Evaluation of Coated Top Foil Bearings: Dry Friction, Drag Torque, and Dynamic Force Coefficients

2018 ◽  
Author(s):  
Luis San Andrés ◽  
Wonbae Jung
Keyword(s):  
Friction Coefficient ◽  
Dry Friction ◽  
Loss Factor ◽  
Static Load ◽  
Sliding Friction ◽  
Dry Sliding ◽  
Drag Torque ◽  
Specific Load ◽  
Foil Bearings ◽  
Mos2 Coating

Despite their many advantages, bump-type foil bearings (BFBs) have issues of dry-friction during sliding contact at rotor start/stop cycles. To prevent premature wear of both shaft and the BFB, the proper selection and application of a coating on the top foil is of importance to ensure bearing long life. This thesis presents measurements characterizing the static and dynamic load performance of a Generation I BFB having uncoated and coated (VN, TiSiN, MoS2) top foils. The bearing, with length L and diameter D = 38 mm, integrates a 360° 0.127 mm thick top foil made of Inconel X-750, and a 27 bumps strip layer, 0.47 mm in height, made of the same stock as for the top foils. The VN and TiSiN coating, 0.005 mm thick, applies to the front and back surfaces of a top foil. The MoS2 coating, 0.020 mm thick, is sacrificial. The tests were conducted at room temperature (21°C), determined by the existing test facility. The dry-sliding torque (T) increases linearly with an increase in applied static load, max W/(LD) = 25.6 kPa. The bearing with a VN coated top foil shows the largest turning torque. The dry-sliding friction factor f = T/(½WD) decreases as the specific load (W/(LD)) increases. As expected, journal rotation towards the top foil free end (clockwise) produces a larger f than for rotations in reverse. A test-rig records the BFB drag torque during rotor acceleration and deceleration procedures to/from 70 krpm (138 m/s). The vertical load applied into a bearing equals W/(LD) = −8.0 kPa, 0 kPa and 8.0 kPa. In general, the bearing with a coated top foil shows a lesser drag torque than that of the uncoated top foil bearing. Among the coated foil bearings, the one with VN coating shows the highest drag torque, whereas another with MoS2 coating shows the lowest. When the rotor starts up, the dry-sliding friction coefficient (f) of the bearing with VN coating is ∼0.4 while f for the bearing with TiSiN coating is 0.3∼0.4. The uncoated bearing shows the largest f ∼0.6, and the MoS2 coated one has the lowest f = 0.2∼0.3. The drag torque, increasing with an increase in applied static load, is small when the rotor is airborne (lesser than ∼10% of peak torque). Dynamic load tests spanning excitation frequencies (ω) from 200 Hz to 400 Hz serve to identify force coefficients for the test BFBs with a specific load of 16 kPa and operating with shaft speed at 50 krpm (833 Hz). Baseline measurements correspond to a null applied load and no shaft rotation. The test bearings show a remarkable behavior with nearly isotropic direct coefficients and very small cross-coupled ones. The bearing direct stiffnesses (K) increase with frequency whereas the direct damping coefficients (C) quickly decrease. The bearing material loss factor, γ = ωC/K, represents best the BFB ability to dissipate mechanical energy. Over the excitation frequency range, γ = 0.34, 0.28, and 0.12 for the uncoated top foil, VN coated and TiSiN coated bearings. The test data show the bearing loss factor correlates with the dry friction coefficient as γ ∼ (0.71 × f) at a rotor speed of 50 krpm (95 m/s). Since the top foils with VN or TiSiN are coated on both sides, kinetic friction between the back of a top foil and the bumps’ crests likely lessens during sustained contact.

A Feasibility Study of Controllable Gas Foil Bearings With Piezoelectric Materials Via Rotordynamic Model Predictions

2018 ◽  
Vol 141 (2) ◽  
Author(s):  
Jisu Park ◽  
Kyuho Sim
Keyword(s):  
Film Thickness ◽  
Piezoelectric Materials ◽  
Input Voltage ◽  
Dynamic Force ◽  
Critical Speeds ◽  
Foil Bearings ◽  
Bearing Clearance ◽  
Operation Conditions ◽  
Lubrication Performance ◽  
Clearance Control

This study presents a new concept of controllable gas foil bearings (C-GFBs) with piezoelectric actuators. The C-GFB consists of a laminated top foil, bump foil, and piezo stacks and can simply change the bearing shape or film thickness locally and globally by varying the thickness of the piezo stacks with input voltages. The control schemes are (1) clearance control: the bearing clearance adjusted by changing overall piezo stack thickness, and (2) preload control: the mechanical preload modulated by the thickness expansion of several piezo stacks. Bearing lubrication performance is predicted for four cases of C-GFBs with different bearing clearances and preloads. The piezo stack control generates meaningful differences in the fluid-film thickness and pressure. Clearance control has a great effect on the dynamic force coefficients, but preload control slightly increases. Furthermore, the rotordynamic prediction of a rotor supported on two journal C-GFBs is conducted. As a result, both control modes for C-GFB are found to have a positive effect on rotordynamic amplitudes. Finally, using the orbit simulations, the C-GFB is controlled to have a small bearing clearance and large preload at critical speeds to make it possible to stably pass through the critical speeds. Consequently, it turns out that the C-GFB can improve bearing lubrication and rotordynamic performances by controlling only the input voltage of the piezo stacks. In addition, the C-GFB can be used to form various shapes to meet the operation conditions of an applied system.

The Wing Foil: A Novel Compliant Radial Foil Bearing Design

2017 ◽  
Author(s):  
Erik E. Swanson ◽  
P. Shawn O’Meara
Keyword(s):  
Test Data ◽  
High Performance ◽  
State Of The Art ◽  
Design Features ◽  
Critical Speeds ◽  
Foil Bearings ◽  
Foil Bearing ◽  
Support Element ◽  
Bearing Design ◽  
Multidimensional Array

To meet the challenging demands for high performance, affordable compliant foil bearings, a novel compliant support element has been developed. This recently patented, novel support element uses a multidimensional array of multiple, formed, cantilever “wing foil” tabs. The wing foil bearing has all the features required to achieve state of the art performance (Gen III for radial bearings). This paper describes two radial foil beings using the wing foil and the unique design features. Test data for a 31.75 mm diameter bearing operating in air and in steam up to 42 krpm are presented to demonstrate the performance of this bearing. It is shown to have low subsynchronous vibration and reasonable damping through rigid shaft critical speeds.

Thermohydrodynamic Analysis of Bump Type Gas Foil Bearings: A Model Anchored to Test Data

2010 ◽  
Vol 132 (4) ◽  
Author(s):  
Luis San Andrés ◽  
Tae Ho Kim
Keyword(s):  
Test Data ◽  
Thermal Energy ◽  
Gas Flow ◽  
Energy Transport ◽  
Static Load ◽  
Isothermal Condition ◽  
Gas Temperature ◽  
Foil Bearings ◽  
Foil Bearing ◽  
Forced Cooling

The paper introduces a thermohydrodynamic (THD) model for prediction of gas foil bearing (GFB) performance. The model includes thermal energy transport in the gas film region and with cooling gas streams, inner or outer, as in typical rotor-GFBs systems. The analysis also accounts for material property changes and the bearing components’ expansion due to temperature increases and shaft centrifugal growth due to rotational speed. Gas inlet feed characteristics are thoroughly discussed in bearings whose top foil must detach, i.e., not allowing for subambient pressure. Thermal growths determine the actual bearing clearance needed for accurate prediction of GFB forced performance, static and dynamic. Model predictions are benchmarked against published measurements of (metal) temperatures in a GFB operating without a forced cooling gas flow. The tested foil bearing is proprietary; hence, its geometry and material properties are largely unknown. Predictions are obtained for an assumed bearing configuration, with bump-foil geometry and materials taken from prior art and best known practices. The predicted film peak temperature occurs just downstream of the maximum gas pressure. The film temperature is higher at the bearing middle plane than at the foil edges, as the test results also show. The journal speed, rather than the applied static load, influences more the increase in film temperature and with a larger thermal gradient toward the bearing sides. In addition, as in the tests conducted at a constant rotor speed and even for the lowest static load, the gas film temperature increases rapidly due to the absence of a forced cooling air that could carry away the recirculation gas flow and thermal energy drawn by the spinning rotor; predictions are in good agreement with the test data. A comparison of predicted static load parameters to those obtained from an isothermal condition shows the THD model producing a smaller journal eccentricity (larger minimum film thickness) and larger drag torque. An increase in gas temperature is tantamount to an increase in gas viscosity, hence, the noted effect in the foil bearing forced performance.

Effects of Mesh Density on Static Load Performance of Metal Mesh Gas Foil Bearings

2011 ◽  
Vol 134 (1) ◽  
Author(s):  
Yong-Bok Lee ◽  
Chang Ho Kim ◽  
Tae Ho Kim ◽  
Tae Young Kim
Keyword(s):  
Test Data ◽  
Loss Factor ◽  
Static Load ◽  
Stiffness Coefficient ◽  
Metal Mesh ◽  
Rotor Spinning ◽  
Foil Bearings ◽  
Mesh Density ◽  
Damping Loss Factor ◽  
Mesh Structures

Metal mesh materials have been used successfully in vibration isolators and bearing dampers due to their superior friction or hysteresis damping mechanism. These materials are formed to metal mesh (or wire mesh) structures in ring-shape by compressing a weave of metal wires, in general. Recently, oil-free rotating machinery implement metal mesh structures into hydrodynamic gas foil bearings by replacing bump strip layers with them, to increase its bearing structural damping. A metal mesh foil bearing (MMFB) consists of a top foil and support elastic metal mesh pads installed between a rotating shaft and a housing. The present research presents load capacity tests of a MMFB at rotor rest (0 rpm) and 30 krpm for three metal mesh densities of 13.1%, 23.2%, and 31.6%. The metal mesh pad of test MMFB is made using a stainless steel wire with a diameter of 0.15 mm. Test rig comprises a rigid rotor with a diameter of 60 mm supported on two ball bearings at both ends and test MMFB with an axial length of 50 mm floats on the rotor. Static loads is provided with a mechanical loading device on test MMFB and a strain gauge type load cell measures the applied static loads. A series of static load versus deflection tests were conducted for selected metal mesh densities at rest (0 rpm). Test data are compared to further test results of static load versus journal eccentricity recorded at the rotor speed of 30 krpm. Test data show a strong nonlinearity of bearing deflection (journal eccentricity) with static load, independent of rotor spinning. Observed hysteresis loops imply significant structural damping of test MMFB. Measured journal deflections at 0 rpm are in similar trend to recorded journal eccentricities at the finite rotor speed; thus implying that the MMFB performance depends mainly on the metal mesh structures. The paper also estimates linearlized stiffness coefficient and damping loss factor of test MMFB using the measured static load versus deflection test data at 0 rpm and 30 krpm. The results show that the highest mesh density of 31.6% produces highest linearlized stiffness coefficient and damping loss factor. With rotor spinning at 30 krpm, the linearlized stiffness coefficient and damping loss factor decrease slightly, independent of metal mesh densities. The present test data will serve as a database for benchmarking MMFB predictive models.

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