2011 ASME Turbo Expo Congress Exhibition Parametric

2011 ASME Turbo Expo Congress & Exhibition Parametric Study of Bump Foil Gas Bearings for Industrial Applications GT 2011 -46767 Oscar De Santiago CIATEQ A. C. Queretaro, Qro, Mexico http: //rotorlab. tamu. edu http: //www. ciateq. mx/ Luis San Andres Texas A&M University College Station, TX, USA 1

Oil-Free Bearings for Turbomachinery Justification Current advancements in vehicle turbochargers and midsize gas turbines need of proven gas bearing technology to procure compact units with improved efficiency in an oil-free environment. Also, Oil-free turbomachinery and subsea compression are among major focuses in modern energy industry. DOE, DARPA, NASA interests range from applications as portable fuel cells (< 60 k. W) in microengines to midsize gas turbines (< 250 k. W) for distributed power and hybrid vehicles. Gas Bearings allow • weight reduction, energy and complexity savings • higher temperatures, without needs for cooling air • improved overall engine efficiency 2

Available Bearing Technologies Magnetic bearings • Low to medium temperatures • Moderate loads • Need control systems • Need back-up bearings • Long history of operation in some specific industrial applications www. skf. com, 2011 www. synchrony. com, 2011 Schweitzer/Maslen 2009 • Current Magnetic Bearing solution is expensive and even more expensive (and difficult) to make it reliable 3

Available Bearing Technologies Rolling element bearings • Low temperatures • Low DN limit (< 2 M) • Need lubrication system Herringbone grooved bearing NICH Center, Tohoku University AIAA 2004 -4189 • Precision fabrication process Power. MEMS 2003 GAS BEARINGS • Low load capacity and stiffness and little damping Gas Foil Bearing Flexure Pivot Bearing • Oil-Free • NO DN limit • Low friction and power loss • Thermal management AIAA-2004 -5720 -984 4 GT 2004 -53621

Microturbomachinery as per IGTI Distributed power (Hybrid Gas turbine & Fuel Cell), Hybrid vehicles Drivers: deregulation in distributed power, environmental needs, increased reliability & efficiency ASME Paper No. GT 2002 -30404 Honeywell, Hydrogen and Fuel Cells Merit Review Automotive turbochargers, turbo expanders, compressors, Max. Power ~ 250 k. Watt 5 International Gas Turbine Institute

Micro Gas Turbines Microturbine Power Conversion Technology Review, ORNL/TM-2003/74. Cogeneration systems with high efficiency • Multiple fuels (best if free) • 99. 99 X% Reliability • Low emissions • Reduced maintenance • Lower lifecycle cost 60 k. W MGT MANUFACTURER OUTPUT POWER (k. W) Bowman 25, 80 Capstone 30, 60, 200 Elliott Energy Systems 35, 60, 80, 150 General Electric 175 Ingersoll Rand 70, 250 Turbec, ABB & Volvo 100 Hybrid System : MGT with Fuel Cell can reach efficiency > 60% www. microturbine. com Ideal to replace reciprocating engines. Low footprint desirable 6

Examples of commercial applications Micro Turbines • Capstone of California 7 Turbo chargers • Honeywell “on the race”

Examples of commercial applications Industrial Air Compressors • Samsung’s successful Micro Turbo Master line of compressors feature gas foil bearings • Pressures up to 130 psig • Powers up to 0. 13 MW • Samsung has another line (Turbo Master) of air compressors with pressures up to 300 psig and power up to 2. 4 MW (~20 x larger). Run on TPJB. What’s next ? ? 8 www. samsungtechwin. com, 2011

MTM – Needs, Hurdles & Issues Largest power to weight ratio, Compact & low # of parts High energy density Reliability and efficiency, Low maintenance Extreme temperature and pressure Environmentally safe (low emissions) Lower lifecycle cost ($ k. W) High speed Rotordynamics & (Oil-free) Bearings & Sealing Materials Coatings: surface conditioning for low friction and wear Ceramic rotors and components Manufacturing Automated agile processes Cost & number Processes & Cycles Low-NOx combustors for liquid & gas fuels TH scaling (low Reynolds #) Fuels Best if free (bio-fuels) 9

Gas Bearings for Oil-Free MTM Advantages of gas bearings over oil-lubricated bearings – Process gas is cleaner and eliminates contamination by buffer lubricants – Gases are more stable at extreme temperatures and speeds (no lubricant vaporization, cavitation, solidification, or decomposition) – Gas bearing systems are lower in cost: less power usage and small friction, enabling savings in weight and piping Gas Bearings Must Be Simple! 10

Ideal gas bearings for MTM Load Tolerant – capable of handling both normal and extreme bearing loads without compromising the integrity of the rotor system. Simple – low cost, small geometry, low part count, constructed from common materials, manufactured with elementary methods. High Rotor Speeds – no specific speed limit (such as DN) restricting shaft sizes. Small Power losses. Good Dynamic Properties – predictable and repeatable stiffness and damping over a wide temperature range. Reliable – capable of operation without significant wear or required maintenance, able to tolerate extended storage and handling without performance degradation. +++ Modeling/Analysis (anchored to test data) available 11

Gas Bearings for MTM What are the needs? Make READY technology for industrial application by PUSHING development to • make out of the shelf item with proven results for a wide range of applications; • engineered product with well known manufacturing process; • known (verifiable) performance with solid laboratory and field experiences 12

Gas Bearings Research at TAMU See References at end Thrust: Investigate conventional bearings of low cost, easy to manufacture (common materials) and easy to install & align. Combine hybrid (hydrostatic/hydrodynamic) bearings with low cost coating to allow for rub-free operation at start up and shut down Major issues: Little damping, Wear at start & stop, Nonlinear behavior (subsync. whirl) 13

Gas Bearing Research at TAMU 2001/2 - Three Lobe Bearings Stability depends on feed pressure. Stable to 80 krpm with 5 bar pressure 2003/4 - Rayleigh Step Bearings Worst performance to date with grooved bearings 2002 -09 - Flexure Pivot Tilting Pad Bearings Stable to 93 krpm w/o feed pressure. Operation to 100 krpm w/o problems. Easy to install and align. 2004 -11: Bump-type Foil Bearings Industry standard. Reliable but costly. Models anchored to test data. 2008 -12: Metal Mesh Foil Bearings Cheap technology. Still infant. Users needed See References at end 14

Gas Foil Bearings 15

Gas Foil Bearings Advertised advantages: high load capacity (>20 psig), rotordynamically stable, tolerance of misalignment and shocks 16

Gas Foil Bearings – Bump type • Series of corrugated foil structures (bumps) assembled within a bearing sleeve. • Integrate a hydrodynamic gas film in series with one or more structural layers. Applications: APUs, ACMs, micro gas turbines, turbo expanders • Reliable • Tolerant to misalignment and debris, also high temperature • Need coatings to reduce friction at start-up & shutdown • Damping from dry-friction and operation with limit cycles 17

Foil Bearings (+/-) • • • Increased reliability: load capacity (< 20 psi) No lubricant supply system, i. e. reduce weight High and low temperature capability (> 1, 000 C) No scheduled maintenance Tolerate high vibration and shock load. Quiet operation • Endurance: performance at start up & shut down (lift off speed) • Little test data for rotordynamic force coefficients & operation with limit cycles (sub harmonic motions) • Thermal management for high temperature applications (gas turbines, turbochargers) • Predictive models lack validation for GFB operation 18 at HIGH TEMPERATURE

Computational analysis 19

Theoretical basis • Solve Reynolds equation for compressible flow (isothermal case). • Coupled to bump metal sheet deformation (nonlinear stiffness and damping). • Iterative solution to find bearing equilibrium position. • Perturbation analysis to find dynamic performance (frequency-dependent stiffness and damping coefficients). Refs: San Andrés (2009), Arghir (2004), Iordanoff (1999), Heshmat (1992) 20

The computational program • Windows OS and MS Excel 2003 (minimum requirements) • Fortran 99 Executables for FE underspring structure and gas film analyses. Prediction of forced – static & dynamic- performance. • Excel® Graphical User Interface (US and SI physical units). Input & output (graphical) • Compatible with XLTRC 2 and XLROTOR codes Code: XL_GFBTHD 21

Graphical User Interface Worksheet: Shaft & Bearing models (I) 22

Graphical User Interface Worksheet: Shaft & Bearing models (II) 23

Graphical User Interface Worksheet: Top Foil and Bump Models 24

Graphical User Interface Worksheet: Foil Bearing (Operation and Results) 25

Parametric Study 26

Results • Example bearing (Ref [3]): • Bump unit area stiffness lowers as bump pitch increases • Bump unit area stiffness increases with foil thickness 27

Results Measured load capacity (Ref [3]) 31 psi Current predictions, constant load of 31 psi Calibration point 1 Calibration point 2 • Benchmarking with independent experiments – Generation 1 bearing (Ref [3]). • Used to find practical limit of film thickness 28

Results • Base bearing (Ref [3]): 29

Rule of thumb for design From observations of bump stiffness and bearing performance predictions: • Bearing scaling: use Della Corte´s rule: W ~ N L D^2 • Bump scaling: Knew = Korig / f ; f is de diameter scale factor 30

Application example • Industrial compressor for injection service • 8 impellers, 640 lb rotor Bearing characteristics Rotor Diameter, D Length, L Radial clearance, * Load, W W/LD 132 mm (5. 21 in) 169 mm (6. 64 in) c 96 µm (3. 8 mil) 1, 421 N (319 lb) 0. 636 bar (9. 21 psi) • Re-configured rotor – move bearings INBOARD of gas seals • Use larger diameter at bearing location Expected speed range: 3 to 20 krpm 13 -15 krpm MCOS most typical 31

Application - rotordynamics Linear stability analysis Predicted stiffness range 5 th Compressor can´t cross these speeds (requires more damping) 32

Observations – Conceptually, scaled gas foil bearings can support an industrial, flexible rotor. – Re-location of bearings is necessary to decrease unit load, but it is feasible in the compressor working environment. – Rotor-bearing system requires additional damping to control shaft vibration at critical speeds. 33

Closure Dominant challenges for gas bearing technology: – Low gas viscosity requires minute clearances to generate load capacity. – Damping & rotor stability are crucial – Inexpensive coatings to reduce drag and wear – Bearing design & manufacturing process well known – Adequate thermal management to extend operating envelope into high temperatures 34

Closure Other pressing challenges for gas bearing technology: intermittent contact and damaging wear at startup & shut down, and temporary rubs during normal operating conditions Current research focuses on Need Low coatings (materials), Cost & rotordynamics (stability) & high Long Life temperature (thermal management) Solution! 35

Oil-Free Bearings for Turbomachinery References 36

References Foil Bearings ASME GT 2011 -46767 De Santiago, O. , and San Andrés, L. , 2011, “Parametric Study of Bump Foil Gas Bearings for Industrial Applications” ASME GT 2011 -45763 San Andrés, L. . , and Ryu, K. , 2011, “On the Nonlinear Dynamics of Rotor-Foil Bearing Systems: Effects of Shaft Acceleration, Mass Imbalance and Bearing Mechanical Energy Dissipation. ” ASME GT 2010 -22508 Howard, S. , and San Andrés, L. , 2011, “A New Analysis Tool Assessment for Rotordynamic Modeling of Gas Foil Bearings, ” ASME J. Eng. Gas Turbines and Power, v 133 NASA/TM 2010 -216354 ASME GT 2010 -22981 San Andrés, L. , Ryu, K. , and Kim, T-H, 2011, “Thermal Management and Rotordynamic Performance of a Hot Rotor-Gas Foil Bearings System. Part 2: Predictions versus Test Data, ” ASME J. Eng. Gas Turbines and Power, v 133 ASME GT 2010 -22981 San Andrés, L. , Ryu, K. , and Kim, T-H, 2011, “Thermal Management and Rotordynamic Performance of a Hot Rotor-Gas Foil Bearings System. Part 1: Measurements, ” ASME J. Eng. Gas Turbines and Power, v 133 8 th IFTo. MM Int. Conf. San Andrés, L. , Camero, J. , Muller, S. , Chirathadam, T. , and Ryu, K. , 2010, on Rotordynamics “Measurements of Drag Torque, Lift Off Speed, and Structural Parameters in a 1 st Generation Floating Gas Foil Bearing, ” Seoul, S. Korea (Sept. ) ASME GT 2009 -59920 San Andrés, L. , Kim, T. H. , Ryu, K. , Chirathadam, T. A. , Hagen, K. , Martinez, A. , Rice, B. , Niedbalski, N. , Hung, W. , and Johnson, M. , 2009, “Gas Bearing Technology for Oil. Free Microturbomachinery – Research Experience for Undergraduate (REU) Program at Texas A&M University AHS 2009 paper Kim, T. H. , and San Andrés, L. , 2010, “Thermohydrodynamic Model Predictions and Performance Measurements of Bump-Type Foil Bearing for Oil-Free Turboshaft Engines 37 in Rotorcraft Propulsion Systems, ” ASME J. of Tribology, v 132

References Foil Bearings ASME GT 2009 -59919 San Andrés, L. , and Kim, T. H. , 2010, “Thermohydrodynamic Analysis of Bump Type gas Foil Bearings: A Model Anchored to Test Data, ” ASME J. Eng. Gas Turbines and Power, v 132 IJTC 2008 -71195 Kim, T. H. , and San Andrés, L. , 2009, "Effects of a Mechanical Preload on the Dynamic Force Response of Gas Foil Bearings - Measurements and Model Predictions, " Tribology Transactions, v 52 ASME GT 2008 -50571 IJTC 2007 -44047 Kim, T. H. , and San Andrés, L. , 2009, “Effect of Side End Pressurization on the Dynamic Performance of Gas Foil Bearings – A Model Anchored to Test Data, ” ASME J. Eng. Gas Turbines and Power, v 131. 2008 Best PAPER Rotordynamics IGTI ASME GT 2007 -27249 San Andrés, L. , and Kim, T. H. , 2009, “Analysis of Gas Foil Bearings Integrating FE Top Foil Models, ” Tribology International, v 42 AIAA-2007 -5094 San Andrés, L. , and T. H. Kim, 2007, “Issues on Instability and Force Nonlinearity in Gas Foil Bearing Supported Rotors, ” 43 rd AIAA/ASME/SAE/ASEE Joint Propulsion Conference, Cincinnati, OH, July 9 -11 ASME GT 2005 -68486 Kim, T. H. , and L. San Andrés, 2008, “Heavily Loaded Gas Foil Bearings: a Model Anchored to Test Data, ” ASME J. Eng. Gas Turbines and Power, v 130 ASME GT 2006 -91238 San Andrés, L. , D. Rubio, and T. H. Kim, 2007, “Rotordynamic Performance of a Rotor Supported on Bump Type Foil Gas Bearings: Experiments and Predictions, ” ASME J. Eng. Gas Turbines and Power, v 129 ASME GT 2004 -53611 San Andrés, L. , and D. Rubio, 2006, “Bump-Type Foil bearing Structural Stiffness: Experiments and Predictions, ” ASME J. Eng. Gas Turbines and Power, v 128 38

References Metal mesh foil bearings ASME GT 2011 -45274 San Andrés, L. , and Chirathadam, T. , 2011, “Metal Mesh Foil Bearings: Effect of Excitation Frequency on Rotordynamic Force Coefficients ASME GT 2010 -22440 San Andrés, L. , and Chirathadam T. A. , 2010, “Identification of Rotordynamic Force Coefficients of a Metal Mesh Foil Bearing Using Impact Load Excitations. ” ASME GT 2009 -59315 San Andrés, L. , Chirathadam, T. A. , and Kim, T. H. , 2009, “Measurements of Structural Stiffness and Damping Coefficients in a Metal Mesh Foil Bearing. ” AHS Paper San Andrés, L. , Kim, T. H. , Chirathadam, T. A. , and Ryu, K. , 2009, “Measurements of Drag Torque, Lift-Off Journal Speed and Temperature in a Metal Mesh Foil Bearing, ” American Helicopter Society 65 th Annual Forum, Grapevine, Texas, May 27 -29 Other ASME DETC 200734136 Gjika, K. , C. Groves, L. San Andrés, and G. La. Rue, 2007, “Nonlinear Dynamic Behavior of Turbocharger Rotor-Bearing Systems with Hydrodynamic Oil Film and Squeeze Film Damper in Series: Prediction and Experiment. ” 39

CIATEQ´s full-size rotordynamic rig 40

Acknowledgments Thanks to NSF (Grant # 0322925) NASA GRC (Program NNH 06 ZEA 001 N-SSRW 2), Capstone Turbines, Inc. , Honeywell Turbocharging Systems, Korea Institute of Science and Technology (Dr. Tae. Ho Kim) Foster-Miller, Mi. TI, TAMU Turbomachinery Research Consortium (TRC) CIATEQ A. C. Learn more: http: //rotorlab. tamu. edu 41