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Luis San Andrés Mast-Childs Professor Fellow ASME

ASME TURBO EXPO 20 11 , Vancouver, Canada (June 2011). Metal Mesh Foil Bearing Effect of Motion Amplitude, Rotor Speed, Static Load, and Excitation Frequency on Force Coefficients. Thomas Abraham Chirathadam Research Assistant. Luis San Andrés Mast-Childs Professor Fellow ASME.

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Luis San Andrés Mast-Childs Professor Fellow ASME

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  1. ASME TURBO EXPO 2011,Vancouver, Canada (June 2011) Metal Mesh Foil Bearing Effect of Motion Amplitude, Rotor Speed, Static Load, and Excitation Frequency on Force Coefficients Thomas Abraham Chirathadam Research Assistant Luis San Andrés Mast-Childs Professor Fellow ASME Texas A&M University ASME GT2011-45257 ASME J. Eng Gas Turbines & Power (in print) Presentation available at http://rotorlab.tamu.edu

  2. 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. DOE, DARPA, NASA interests range from applications as portable fuel cells (< 60 kW) in microengines to midsize gas turbines (< 250 kW) for distributed power and hybrid vehicles. • Gas Bearingsallow • weight reduction, energy and complexity savings • higher temperatures, without needs for cooling air • improved overall engine efficiency

  3. Ideal gas bearings 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

  4. Gas Foil Bearings Used in many oil-free rotating machinery:high load capacity (>20 psig), rotordynamically stable, tolerance of misalignment and shocks……. …… but expensive with intellectual property restrictions. A low cost proven alternative needed.

  5. Metal Mesh Foil Bearing (MMFB) 5 cm MMFB COMPONENTS: Bearing cartridge, metal mesh ring and top Foil Hydrodynamic air film develops between rotating shaft and top foil. Potential applications:ACMs, micro gas turbines, turbo expanders, turbo compressors, turbo blowers, automotive turbochargers, APUs Metal mesh foil bearing • Large damping (material hysteresis) offered by metal mesh • Tolerant to misalignment, and applicable to a wide temperature range • Coatings needed to reduce friction at start-up & shutdown

  6. MMFB components Metal mesh pad Compressed weave of copper wires Compactness (density)=20% Stiffness and damping of MMFB depend on metal mesh compactness Top Foil 0.12 mm top foil Chrome-Nickel alloy Rockwell 40/45 Heat treated at ~ 450 ºC for 4 hours and allowed to cool. Foil retains arc shape after heat treatment Sprayed with MoS2 sacrificial coating Bearing cartridge (+top foil+ metal mesh) Metal mesh pad and top foil inserted in steel bearing cartridge. Top foil firmly affixed in a thin slot made with wire-EDM machining Simple to manufacture and assemble

  7. Past work in Metal Mesh Dampers METAL MESH DAMPERS provide large amounts of damping. Inexpensive component. Zarzour and Vance (2000)J. Eng. Gas Turb. & Power, Vol. 122 Advantages of Metal Mesh Dampers over SFDs Capable of operating at low and high temperatures No changes in performance if soaked in oil Al-Khateeb and Vance (2001)ASME GT-2001-0247 Test metal mesh donut and squirrel cage( in parallel) Metal Mesh damping not affected by modifying squirrel cage stiffness Choudhry and Vance (2005)ASME GT-2005-68641 Develop design equations, empirically based, to predict structural stiffness and viscous damping coefficient

  8. Metal Mesh Dampers in Hybrid bearings Recent work by OEM with MM dampers to maximize load capacity and to add damping in gas bearings Ertas &Luo (2008)ASME J. Gas Turbines Power, 130 MM damper force coefficients not affected by shaft eccentricity (or applied static load) Ertas (2009) ASME J. Gas Turbines Power, 131 Two metal mesh rings installed in a multiple pad gas bearing with flexural supports to maximize load capacity and damping. Bearing stiffness decreases with frequency & w/o external pressurization; and increases gradually with supply pressure Ertas et al. (2009)AIAA 2009-2521 Shape memory alloy (NiTi) shows increasing damping with motion amplitudes. Damping from NiTi larger than for Cu mesh (density – 30%) : large motion amplitudes (>10 um)

  9. Past work in MMFBs San Andrés et al. (2010)J. Eng. Gas Turb. & Power, 132(3) Assembled the first prototype MMFB (L=D=28 mm). Load vs Deflection with hysteresis shows large structural damping (g~ 0.7). Frequency dependentstiffness agree with predictions. San Andrés et al. (2009)ASME GT2009-59920 Demonstrated operation to 45 krpm with early rotor lift off. Educated undergraduate students. San Andrés et al. (2010)J. Eng. Gas Turb. & Power, 132 Start and shut down to measure torque and lift-off speed. Low friction factor ~ 0.01 at high speed 60 krpm. San Andrés and Chirathadam (2011)J. Eng. Gas Turb. & Power, 133 Rotordynamic coefficients from unidirectional impact loads. Estimated stiffness and damping force coefficients at 50 krpm.

  10. EXPERIMENTS with a PRIOR MMFB (larger mesh thickness) Structural stiffness and damping Friction factor with airborne operation

  11. MMFB structural stiffness vs. freq. Bearing stiffness is frequency and motion amplitude dependent 12.7 mm Motion amplitudeincreases At low frequencies (25-100 Hz), stiffness decreases At higher frequencies, stiffness gradually increases 25.4 mm 38.1 mm San Andres et al., 2010, ASME J. Eng. Gas Turbines Power, 132 (3) Al-Khateeb & Vance model

  12. MMFB eq. damping vs. frequency Amplitude increases MMFB equiv. viscous damping decreases as the excitation frequency increases and as motion amplitude increases 12.7 μm 25.4 μm 38.1 μm San Andres et al., 2010, ASME J. Eng. Gas Turbines Power, 132 (3) Al-Khateeb & Vance model

  13. Friction coefficient vs rotor speed Increasing static load (Ws) to 35.6 N (8 lb) Dead weight (WD= 3.6 N) 8.9 N (2 lb) 17.8 N (4 lb) 26.7 N (6 lb) 35.6 N (8 lb) f = (Torque/Radius)/(Net static load) f ~ 0.01 Friction coefficient ( f ) decreases with increasing static load Rotor accelerates f rapidly decreases initially, and then gradually raises with increasing rotor speed Dry sliding Airborne (hydrodynamic)

  14. CURRENT MMFB & ROTORDYNAMIC TEST RIG

  15. MMFB dimensions & materials 2.7mm 5 cm Metal mesh foil bearing Top foil: Chrome nickel alloy Metal mesh: copper Bearing Cartridge: Stainless steel

  16. MMFB rotordynamic test rig Bearing Journal press fitted on Shaft Stub cm 15 10 5 0 TC cross-sectional view Ref. Honeywell drawing # 448655 Max. operating speed: 75 krpm Turbocharger driven rotor Regulated air supply: 9.30bar (120 psig) Twin ball bearing turbocharger, Model T25, donated by Honeywell Turbo Technologies Test Journal: length 55 mm, 36.5 mm diameter

  17. Rotordynamic test rig (X-Y 100 N shakers) Dynamic load : 25-100 N Rotor speed 50 krpm Freq. identification range: 200 to 400 Hz Motion amplitudes : 20mm, 25 mm & 30 mm Static loads: 22 N (15.5 N along X & Y) and 36N

  18. Test rig schematic diagram Oil inlet TC center housing Static load Squirrel cage affixed on turn-knob controlled positioning table Air outlet Thermocouple measures bearing outboard end temperature Shaft stub BEARING Oil outlet Squirrel cage (Soft elastic support) Stinger connection to shaker BEARING Continuous supply of oil lubricates ball bearings in turbocharger center housing Static load along X Static load along Y X Y Load sensor Accelerometer Bearing weight 5 cm Net static load

  19. Impact load tests : system mass & soft structure stiffness Impact load Y Bearing overhang on squirrel cage Accelerance function = physical model equation Sq. cage Bearing Impact load along Y direction Squirrel cage structure stiffness < 10% of bearing stiffness Damping ratio =0.024 Estimated test system mass =0.88 kg

  20. Identification model EOM: KS,CS:soft SQ stiffness and damping MS : effective mass Shaker force, FY KYY, CYY Y Kij ,Cij:test bearing stiffness and damping KXY, CXY KXX, CXX Bearing Ω Journal X Shaker force, FX KSY, CSY KYX, CYX Soft Support structure KSX, CSX

  21. Identification model X Forces: Sine sweep excitations (200-400 Hz), amplitude controlled Responses: measure bearing accelerations and displacements relative to journal Process data in frequency domain to obtain: Kij ,Cij :bearing stiffness and damping vs. frequency

  22. Dynamic load and displacements Dynamic load 25-100 N Excitation frequency 200- 400 Hz Displacement along X ~ 30 mm Noticeable cross-directional motion Force along X X Y Net static load (static load-bearing weight) = 22 N along vertical direction Static load resolved along X and Y = 15.5 N Displacement along X Shaft speed=50 krpm (833 Hz) Displacement along Y

  23. Forces & disps. vs. frequency 200-400 Hz ForceFYY FXX FYX FXY Displacement YY Xx XY YX X Y N Static loads along X and Y =15.5 N Shaft speed=50 krpm (833 Hz) DFT amplitude of dynamic loads and bearing displacements relative to rotor mm Average of ten consecutive excitations In frequency domain, displacement magnitude decreases (force increases) with frequency

  24. MMFBstiffnesses: varying rotor speeds Kxx KYY KYY Kxx KXY KYX KXY KYX KYY KXX KYY KXX KXY KXY KYX KYX 22 N static load At rest (0 rpm) direct stiffness is structural only. Direct K decreases with rotor speed. 0 krpm 40 krpm With rotation, KYX changes sign. Small cross-stiffneses. Direct stiffnesses gradually increase with frequency 50 krpm 45 krpm

  25. MMFBdamping: varying rotor speeds CYY CXX CYX CYY CXX CYX CXY CXY CXX CXX CYY CYY CXY CYX CXY CYX 22 N static load At rest (0 rpm) direct damping is structural only. Direct C decreases with frequency. 0 krpm 40 krpm Rotor speed does not affect damping. Major effect is from metal mesh hysteresis. Direct C increases with frequency. 45 krpm 50 krpm

  26. MMFBstiffnesses: varying motion amplitudes KXX KXX KYY KYY KXY KXY KYX KYX KXX KYY KXY KYX 22 N static load 50 krpm Rotor speed (833 Hz) 20 mm 25 mm Direct stiffnesses decrease with increasing motion amplitudes. Similar to structural test results San Andres et al (2009) At highest displacement amplitude (30 mm), cross-coupled stiffness magnitude is large at ~-0.4 MN/m 30 mm

  27. MMFBdamping: varying motion amplitudes CYY CXX CYY CXX CYX CYX CXY CXY CYY CXX CYX CXY 22 N Static load 50 krpm Rotor speed (833 Hz) 20 mm 25 mm Direct damping decreases slightly with increasing motion amplitude. Direct C increases with frequency. With increasing motion amplitude, cross-damping CYX decreases 30 mm

  28. MMFBK & C: varying applied static load W CXX CYY CYY CXX KXX KXX KYY KYY CYX CXY CYX KXY KXY CXY KYX KYX Net static load = 22 N ( W/LD=0.16 bar) & 36 N ( W/LD=0.26 bar) 36 N 22 N 50 krpm Rotor speed (833 Hz) For increasing static load: force coefficients are similar in magnitude and show same trend in frequency. 36 N 22 N

  29. Energy dissipation in MMFB largely due to mechanical hysteresis. A loss factor (γ) best represents the material damping MMFB: estimation of loss factor Proportional structural damping Energy (material damping) = Energy (viscous damping) For elliptical orbits: For circular orbits,

  30. MMFB: Loss factor vs. frequency Material loss factor (g) is frequency dependent. gdoes not depend greatly on displacement amplitudes, rotor speed or static loads Typical BFB loss factor ~ 0.1- 0.4 Kim et al. (2008) g > 1.0 for all test cases. MMFB has more damping than other types of FBs

  31. Waterfalls of force and displacement 400 Hz 200 Hz Synchronous ( 833 Hz) 400 Hz 200 Hz 22 N static load 50 krpm Rotor speed (833 Hz) Dominant displacement amplitude corresponds to excitation frequency No sub-synchronous whirl detected.

  32. MMFB CONCLUSIONS ASME GT2011-45257 • Rotordynamic force coefficients estimated for various rotor speeds, motion amplitudes and static loads: • MMFB stiffness and damping decrease with increasing bearing displacements. • MMFB direct stiffness and damping largest without journal rotation (structural values). With rotation, cross-stiffnesses are small • MMFB direct stiffness increases with frequency while damping increases when rotor spins. • Similar force coefficients obtained for two static loads: 22 N and 36 N • MMFB loss factor (g) is nearly independent of motion amplitude, rotor speed or applied static load MMFB shows large energy dissipation, g >~ 1.0

  33. MMFB CONCLUSIONS ASME GT2011-45257 Test MMFB is structurally soft with large damping: Mid-range of rule of thumb (ROT) Rule-of-thumb (ROT) model (Dellacorte, 2010) Typical foil bearing stiffness coeff. K~ 2,500-7,500 (L x D)lbf/in3 damping coeff. C~ 0.1-1.0 (L x D)lbf-s/in3 MMFB stiffness coeff. K~ 1,330 (Lx D)lbf/in3 [360 MN/m3] damping coeff. C~ 0.93 (L x D)lbf-s/in3 [252 MN/m3] Net static load (applied load-bearing weight) 22 N ( W/LD=0.16 bar) and 36 N ( W/LD=0.26 bar)

  34. Acknowledgments/ Thanks to • Honeywell Turbocharging Technologies • Turbomachinery Research Consortium Learn more at: http://rotorlab.tamu.edu Questions (?)

  35. Extra slides - >

  36. Comparison: MMFB&BFB Friction factor vs rotor speed Static load Rotor accelerates Rotor accelerates f = (Torque/Radius)/(Static load) Friction coefficient decreases with increasing applied static loads and rotor speed (due to lift-off) BFB MMFB f ~ 0.03 f ~ 0.03

  37. Future work:MMFB force coefficient prediction Top foil p Fixed end Θ Km w Top foil radius with assembled clearance Rectangular finite element with 4 nodes Metal mesh r+c r+cm Rotor Y rp eX r Θt eY Top foil h Θp Θl Metal mesh X 3 4 1 2 z y x Unwrapped Metal mesh and top foil • Analysis steps: • Obtain stiffness matrix for MMFB structure + top foil using FEM. • Assume small amplitude motions about a static position. • Solve Reynolds equations for isothermal, isoviscous ideal gas. • Predict force coefficients using dynamic (perturbed) pressure fields

  38. Future work: High temperature operation Demonstrate high temperature reliable operation of MMFB with adequate thermal management. • Construct two MMFB fitting existing test rig dimensions. • Measure rotor response for temperature as high as 200 ºC, rotor speed up to 50 krpm • c) Compare thermal performance of MMFBs with Gen. I bump-foil bearings Metal Mesh Foil Bearing

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