Design and Manufacturing of Mesoscale Tilting Pad Gas Bearings for 100–200 W Class PowerMEMS Applications

2009 ◽  
Vol 131 (4) ◽  
Author(s):  
Daejong Kim ◽  
Aaron M. Rimpel ◽  
Suk Sang Chang ◽  
Jong Hyun Kim
Keyword(s):  
Natural Frequencies ◽  
Stable Operation ◽  
Scaling Analysis ◽  
Baseline Design ◽  
Gas Bearings ◽  
Tilting Pad ◽  
Design And Manufacturing ◽  
Rotor Bearing ◽  
Bearing Number ◽  
Gas Bearing

This paper introduces a design and manufacturing of mesoscale flexure pivot tilting pad gas bearing with a diameter of 5 mm and a length of 1–2.5 mm for PowerMEMS (micro electromechanical systems for power generation) applications with power ranges of 100–200 W. Potential applications include power source for unmanned air vehicles, small robots, microgas turbines to be harnessed by very small solid oxide fuel cells, microblowers/compressors for microfuel cells, etc. The design studies involve scaling analysis, time-domain orbit simulations for stability analyses, and frequency-domain modal analyses for prediction of rotor-bearing natural frequencies. Scaling analysis indicates that direct miniaturization of macroscale tilting pad gas bearing can result in a large bearing number, which may render the rotor-bearing system unstable. However, the scaling analysis provides the baseline design from which the final design can be derived considering manufacturing issue. The generalized modal analysis using impedance contours predict damped natural frequencies close to those from orbit simulations, providing high fidelity to the developed numerical methods. It was predicted that the designed mesoscale tilting pad gas bearings would show very stable operation up to a maximum simulated speed of 1,000,000 rpm. The designed mesoscale tilting pad gas bearings were manufactured using X-ray lithography and electroplating.

Rotordynamic Performance of Flexure Pivot Tilting Pad Gas Bearings With Vibration Damper

2009 ◽  
Vol 131 (2) ◽  
Author(s):  
Aaron Rimpel ◽  
Daejong Kim
Keyword(s):  
Gas Turbines ◽  
Dynamic Models ◽  
Natural Frequencies ◽  
Clean Energy ◽  
Design Guidelines ◽  
Vibration Damper ◽  
Shell Mass ◽  
Gas Bearings ◽  
Tilting Pad ◽  
Rotor Bearing

Recently, gas-lubricated bearings have drawn enormous attention for clean energy conversion/process systems such as fuel cells, micro-gas-turbines, gas compressors, etc. Among many different types of gas bearings, tilting pad gas bearings have many attractive features such as high rotor-bearing stability and less severe thermal issues (due to multipad configurations) than foil gas bearings. However, extension of the application of the tilting pad gas bearings to flexible rotors and harsh environments with external vibrations/impacts poses significant design challenges. The design problem addressed in this paper is the vibration damper to be integrated with the flexure pivot tilting pad gas bearing (FPTPGB) with and without pad radial compliance. Linear and nonlinear dynamic models of the FPTPGB with vibration damper were developed, and rotordynamic performance was evaluated to prescribe design guidelines for the selection of bearing shell mass and damper properties. Direct numerical integration (time-domain orbit simulations) and linear analyses were employed to predict rotordynamic responses and other interesting behaviors relevant of rotor-bearing systems with the vibration damper. Rotor-bearing systems showed better performance with larger damper stiffness for both with and without radial compliance. However, bearing shell mass showed different tendencies; lower bearing shell mass was shown to be ideal for bearings with radial compliance, while the opposite trend was observed for bearings without radial compliance. Although increasing the degrees of freedom of the system by allowing the bearing shell to move introduces additional natural frequencies, careful design considerations could allow the placement of the natural frequencies outside of the operating range.

Experimental and Analytical Studies on Flexure Pivot Tilting Pad Gas Bearings With Dampers Applied to Radially Compliant Pads

2009 ◽  
Author(s):  
Daejong Kim ◽  
Aaron Rimpel
Keyword(s):  
Simulation Method ◽  
Analysis Tool ◽  
Primary Analysis ◽  
Successful Operation ◽  
Gas Bearings ◽  
Viscoelastic Dampers ◽  
Thermal Growth ◽  
Tilting Pad ◽  
Rotor Bearing ◽  
First Time

Hydrodynamic flexure pivot tilting pad gas bearings (FPTPGBs) can enable successful operation of oil-free microturbomachinery, and FPTPGBs with radially compliant pads (FPTPGB-Cs) permit rotor centrifugal and/or thermal growth to exceed original bearing clearances and achieve higher speeds. This work presents the experimental and analytical study of such bearings and the application of dampers behind the pad radial compliance structure. A time domain orbit simulation method was implemented as the primary analysis tool to predict rotor-bearing response to imbalance, the presence and location of critical speeds, etc., and compare with test results. Experiments demonstrate the stable hydrodynamic operation of FPTPGBs with a ∼28.6 mm, 0.8 kg rotor above 120 krpm for the first time. The rotor-bearing system was intentionally destabilized in tests by increasing bearing clearances, and viscoelastic dampers added behind the FPTPGB pads delayed the onset of subsynchronous vibrations (from 43 krpm without damper to above 50 krpm with damper). Midrange subsynchronous vibrations of the destabilized system initiated at ∼20 krpm were suppressed by ∼25 krpm due to the stabilizing effect of rotor centrifugal growth. The viscoelastic dampers had a negligible effect on suppressing these midrange subsynchronous vibrations in experiments, but this was not demonstrated in simulations, presumed to be due to much lower stiffness contribution of the damper at lower frequencies.

Experimental and Analytical Studies on Flexure Pivot Tilting Pad Gas Bearings With Dampers Applied to Radially Compliant Pads

2009 ◽  
Vol 131 (4) ◽  
Author(s):  
Aaron Rimpel ◽  
Daejong Kim
Keyword(s):  
Simulation Method ◽  
Analysis Tool ◽  
Primary Analysis ◽  
Successful Operation ◽  
Gas Bearings ◽  
Viscoelastic Dampers ◽  
Thermal Growth ◽  
Tilting Pad ◽  
Rotor Bearing ◽  
First Time

Hydrodynamic flexure pivot tilting pad gas bearings (FPTPGBs) can enable successful operation of oil-free microturbomachinery and FPTPGBs with radially compliant pads permit rotor centrifugal and/or thermal growth to exceed original bearing clearances and achieve higher speeds. This work presents the experimental and analytical study of such bearings and the application of dampers behind the pad radial compliance structure. A time domain orbit simulation method was implemented as the primary analysis tool to predict the rotor-bearing response to imbalance, the presence and location of critical speeds, etc., and to compare with test results. Experiments demonstrate the stable hydrodynamic operation of FPTPGBs with an ∼28.6 mm, 0.8 kg rotor above 120 krpm, for the first time. The rotor-bearing system was intentionally destabilized in tests by increasing bearing clearances and the viscoelastic dampers added behind the FPTPGB pads delayed the onset of subsynchronous vibrations (from 43 krpm without damper to above 50 krpm with damper). Midrange subsynchronous vibrations of the destabilized system initiated at ∼20 krpm were suppressed by ∼25 krpm due to the stabilizing effect of rotor centrifugal growth. The viscoelastic dampers had a negligible effect on suppressing these midrange subsynchronous vibrations in experiments, but this was not demonstrated in simulations, presumed to be due to much lower stiffness contribution of the damper at lower frequencies.

Comparison of Rotordynamic Analysis Predictions With the Test Response of Simple Gas Hybrid Bearings for Oil Free Turbomachinery

2003 ◽  
Author(s):  
Deborah A. Wilde ◽  
Luis San Andre´s
Keyword(s):  
High Speed ◽  
Natural Frequencies ◽  
Damping Ratio ◽  
Rotor Speed ◽  
Gas Bearings ◽  
Model Predictions ◽  
Rotor Bearing ◽  
Frequency Ratios ◽  
Bearing System ◽  
Good Agreement

Current applications of gas film bearings in high-speed oil-free micro-turbomachinery (<0.4 MW) require calibrated predictive tools to successfully deploy their application to mass-produced systems, for example oil-free turbochargers. The present investigation details the linear rotordynamic analysis of a test rotor supported on externally pressurized gas bearings. Model predictions are compared with the test rotordynamic response determined through comprehensive experiments conducted on a small rotor supported on three lobed hybrid (hydrostatic/hydrodynamic) rigid gas bearings. Predictions for the rotor-bearing system synchronous response to imbalance show good agreement with measurements during rotor coast downs, and manifest a decrease in damping ratio as the level of external pressurization increases. The rotor-bearing eigenvalue analysis forwards natural frequencies in accordance with the measurements, and null damping ratios evidence the threshold speeds of rotordynamic instability. Estimated whirl frequency ratios are typically 50% of rotor speed, thus predicting sub synchronous instabilities at lower rotor speeds than found experimentally when increasing the magnitude of feed pressurization. Rationale asserting the nature of the discrepancies calls for further analysis.

Parametric Studies on Dynamic Performance of Hydrostatic Flexure Pivot Tilting Pad Gas Bearing With Radial Compliance

2007 ◽  
Author(s):  
Robert N. Petro ◽  
Daejong Kim
Keyword(s):  
High Speed ◽  
Heat Dissipation ◽  
Optimal Choice ◽  
Hollow Shaft ◽  
Bearing Clearance ◽  
Radial Stiffness ◽  
Hybrid Operation ◽  
Tilting Pad ◽  
Rotor Bearing ◽  
Gas Bearing

Flexure pivot tilting pad gas bearings are recognized as an alternative to foil gas bearing [1, 2] for high speed turbomachinery, due to their capability to provide high rotor-bearing stability and simple structure. The flexure pivot design eliminates wear problem of axial pins or sockets at the pivots which are common in traditional tilting pad bearings. Added features such as a pivot offset and pad preloads can also be optimized to further improve the stability. Hybrid flexure pivot tilting pad gas bearing have also been reported [3]. The hybrid bearing has a direct air supply to the bearing clearance through a tiny orifice. It has shown that the hybrid operation of the tilting pad gas bearing can also increase the rotor-bearing stability [3]. In many microturbomachinery applications, hollow shafts are adopted to reduce the rotor weight and increase the bending critical speeds. However, the hollow shaft has a large centrifugal growth at high speeds requiring the gas bearing to have radial compliances. However, the radial compliance within the tilting pads can compromise the rotor-bearing stability because large displacement of the pads along the radial direction can cause hydrodynamic rotor-bearing instability associated with the increased bearing clearance (i.e. decreased effective preload) if the radial stiffness is not designed properly. Analytical studies show that optimal choice of pad radial stiffness could extend operating envelope of flexure pivot tilting pad gas bearing without deteriorating rotor-bearing stability [4]. High speed operation can generate significant amount of heat and adequate heat dissipation mechanism should also be developed. Hybrid operation is considered to have added benefit of effective cooling capability. This paper presents design studies on hybrid flexure tilting pad gas bearing with radial compliance which can accommodate large rotor centrifugal growth and also provide effective cooling mechanism.

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.

Calculation of Stiffness and Damping Properties of Gas Bearings

1968 ◽  
Vol 90 (4) ◽  
pp. 793-803 ◽  
Author(s):  
J. W. Lund
Keyword(s):  
Static Load ◽  
Journal Bearing ◽  
Computational Method ◽  
Gas Bearings ◽  
Rotating Speed ◽  
Damping Coefficients ◽  
Tilting Pad ◽  
Stiffness And Damping ◽  
Tilting Pad Journal Bearing ◽  
Gas Bearing

The dynamic characteristics of a gas bearing can be represented by a set of spring and damping coefficients (impedances) which are functions of the static load on the bearing, the rotating speed and the whirl frequency of the journal. For a rotor supported in gas bearings, these coefficients can be used directly in a critical speed calculation or an unbalance response calculation. In addition, the coefficients can be employed in a stability investigation. The paper gives the computational method for obtaining the spring and damping coefficients and, also, describes how they are used in rotor calculations and stability studies. Numerical results are given in graphical and tabular form for a tilting pad journal bearing and a three-lobe journal bearing.

Dynamic Response of a Rotor-Hybrid Gas Bearing System Due to Base Induced Periodic Motions

2010 ◽  
Author(s):  
Luis San Andre´s ◽  
Keun Ryu ◽  
Yaying Niu
Keyword(s):  
Natural Frequency ◽  
Excitation Frequency ◽  
Base Plate ◽  
Transportation Systems ◽  
Test Rig ◽  
Periodic Load ◽  
Gas Bearings ◽  
Rotor Bearing ◽  
Gas Bearing ◽  
Bearing System

Rotating machinery in transportation systems experiences intermittent excitation from road conditions. Internal combustion (IC) engines exert (multiple) periodic load excitations into passenger vehicle turbochargers, for example. Too large base motions can produce severe rotor-bearing system damage, even failure. The paper shows the reliability of a rotor-hybrid gas bearing system to withstand intermittent base foundation motions induced by a shaker. The test rig consists of a rigid rotor, 190mm in length, 0.825 kg in mass, and 28.6 mm in diameter, supported on two hybrid, flexure pivot tilting pad type, gas bearings. The whole system, weighing 48 kg, is supported on two soft coil springs and its lowest natural frequency is just ∼5 Hz. The rod connecting the shaker to the base plate is not affixed rigidly to the test rig base. The rod merely pushes on the base plate and hence the induced based motions are intermittent with multiple impacts and frequencies. The base induced motions are at a low main frequency (5–12 Hz) relative to the operating speed of the rotor-bearing system (max. 35 krpm). The recorded rotor responses, relative to the bearing housings, also contain the main excitation frequency and its super harmonics; and because of the intermittency of the base motions, it also excites the rotor-bearing system natural frequency, in particular when the gas bearings are supplied with a low feed pressure. Predicted rotor dynamic displacements induced by the base excitations show reasonable agreement with the test data.

Design and Hydrodynamic Performance of Hybrid Flexural Pivot Gas Bearings for High Speed Oil-Free Micro Turbomachinery

2005 ◽  
Author(s):  
Kyuho Sim ◽  
Daejong Kim
Keyword(s):  
High Speed ◽  
Hydrodynamic Performance ◽  
Bending Vibrations ◽  
Hydrodynamic Mode ◽  
Critical Speeds ◽  
Gas Bearings ◽  
Radial Stiffness ◽  
Tilting Pad ◽  
Rotor Bearing ◽  
Final Design

This paper introduces new flexural pivot tilting pad gas bearings for high speed oil-free micro turbomachinery. The new flexural pivot tilting pad gas bearings have a special web geometry that provides a radial stiffness to accommodate rotor growths and high vibrations at critical speed, a pitching stiffness to accommodate rotor-bearing misalignments or rotor bending vibrations, and a very small tilting stiffness for rotor stability. Comprehensive numerical simulations involving orbit simulations and coast-down simulations were performed to investigate the effects of preloads and pivot offsets on the critical speeds and onset speeds of instability. Higher preload and pivot offset increased both critical speeds of the rotor-bearing system and onset speeds of instability due to the increased wedge effect. Design procedures of radial stiffness were presented considering both rotor centrifugal and thermal growths. From simple adiabatic solution of temperature distribution of gas film under pure hydrodynamic mode, enough bearing clearance at pivot was found to be a very important design aspect for high speed hydrodynamic gas bearings. Asymmetric radial stiffness was chosen as a final design to meet the target design speed of 180 krpm for bearing diameter of 28.52mm. Suggested tilting pad gas bearing with asymmetric radial stiffness was predicted to be very stable even under high external destabilizing forces.

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