32 nd Turbomachinery Research Consortium Meeting Measurements of Rotordynamic Response in a High temperature Rotor Supported on Two Metal Mesh Foil Bearings TRC-BC001-12 Thomas Abraham Chirathadam Research Assistant Luis San Andrés Mast-Childs Professor May 2012 1 TRC Project 32513/1519FB
Metal Mesh Foil Bearing (MMFB) MMFB COMPONENTS: bearing cartridge, WHY METAL MESH ? metal mesh ring and top foil • Large hysteresis damping. Hydrodynamic air film develops between • Wide temperature range rotating shaft and top foil. • Damping unaffected by soaking in oil Bearing Bearing cartridge cartridge • Empirical model available (Vance et al., 2000-2005) Compressed Compressed metal mesh metal mesh pads pads • Hybrid gas bearings with metal mesh improves Heat treated Heat treated overall performance. top foil (Inner top foil (Inner • Enhanced damping surface surface coated with coated with without compromising MoS2) MoS2) stiffness. • Static load does not affect damping Potential applications: ACMs, • Shape memory alloys (expensive) gives + micro gas turbines, turbo expanders, damping as excitation turbo compressors, turbo blowers, amplitude grows automotive turbochargers, APUs 2 (Ertas et al., 2008-20010)
TRC project (1 year) Objective: Demonstrate high temperature reliable operation of MMFB with adequate thermal management. a) Construct two MMFBs fitting test rig. b) Measure rotor response for temperatures to 200 ºC & speed to 50 krpm c) Compare thermal performance: MMFB vs. bump-foil bearing Metal Mesh Foil Bearing 3
TRC Budget Metal Mesh Foil Bearings Year I Support for graduate student (20 h/week) x $ 1,700 x 12 months $ 21,600 Fringe benefits (0.6%) and medical insurance ($191/month) $ 2,419 Travel to (US) technical conference $ 1,200 Tuition three semesters ($3,488 x 3) $ 10,138 Supplies for test rig and construction of test bearings $ 3,200 $ 38,557 Research will characterize, qualitatively and quantitatively, MMFBs of low cost, simple in construction, and suited for high temperature operation. The work is important for turbochargers, turboexpanders and microgas turbines 4
Test rig for high temperature tests Motor driving the rotor End cap holding bearing Test rotor MMFB MMFB Eddy current sensor Test rotor Max. rotor speed 50 krpm Coil heater warms hollow rotor from inside (max 300 C). Imbalance masses added at two ends of rotor (in phase & out of phase) 5
MMFB components Simple to manufacture and assemble Metal mesh pads Top Foil Compressed weave of Bearing cartridge copper wires 0.12 mm top foil ( +top foil+ metal mesh ) Chrome-Nickel alloy Compactness Rockwell 40/45 (density)=20% Metal mesh pads and Heat treated at top foil inserted inside ~ 450 ºC for 4 hours bearing cartridge. and allowed to cool. Stiffness and Foil retains arc shape Top foil firmly affixed damping of MMFB after heat treatment in a thin slot made depend on metal with wire-EDM Sprayed with MoS 2 mesh compactness machining 6 sacrificial coating
Dimensions: rotor and bearings Rotor Inconel 718 Mass, M 1.36 kg Length 200.7 mm Inner diameter, D i 17.90 mm Outer diameter, D O 36.51 mm Rotor diameter at bearings 36.51 mm Bearing span 103 mm Bearings Cartridge outer diameter 50.80 mm Cartridge inner diameter 42.00 mm MMFB with 4 pads Inner diameter, D 36.58 mm Axial length, L 38.10 mm Copper mesh pad thickness 2.6 mm mesh density (compactness) 30 % Wire diameter (mm) 0.30 Number of metal mesh pads 4 Cooling air flow Top foil thickness 0.12 mm rate 160 LPM Top foil (Chrome Nickel steel alloy) Hardness Rockwell (40/45) 7 0.035 mm Radial clearance based on geometry
Predicted MMFB force coefficients W Predictive (in-house) tool models metal mesh pad as a uniform stiffness layer beneath the elastic top foil X Y Drive end bearing 1.2 0.4 K XX Stiffness Cxx Damping 1.0 0.3 CXY CYX K YY Stiffnesses [MN/m] 0.8 Damping [kN.s/m] CYY 0.2 C XX C YY 0.6 Kxx 0.1 C YX KXY 0.4 KYX 0.0 KYY 0.2 0 10 20 30 40 50 60 -0.1 0.0 K YX 0 10 20 30 40 50 60 C XY -0.2 -0.2 K XY Drive end bearing (DEB). Static load = 7.4 N Drive end bearing (DEB). Static load = 7.4 N -0.4 -0.3 rotor speed (krpm) rotor speed (krpm) Direct stiffness increases 80% with speed. Damping drops! 8 Small cross- K’ s
Critical speeds and damping ratios Coupling added mass and inertia Imbalance planes Critical speeds < 10 krpm b/c MMFBs 0.04 bearings are soft. Rigid rotor 5 6 8 9 10 11 12 16 7 13 14 15 0.02 Shaft Radius [m] modes: conical and cylindrical. 4 3 Rotor 2 1 0 Natural frequency [rpm] 50000 -0.02 FREE forward DRIVE backward forward f=6308.8 cpm backward 40000 END END d=.1287 zeta f=7665.2 cpm MMFB supports N=10000 rpm d=.1901 zeta N=10000 rpm -0.04 Flexible coupling 30000 -0.06 0 0.04 0.08 0.12 0.16 0.2 0.24 20000 Axial Location [m] 10000 Model rotor-bearing system 0 0. 10000. 20000. 30000. 40000. 50000. Rotor speed [rpm] 0.3 0.25 Conical forward whirl Damping ratio 0.2 Damping decreases with speed. Cylindrical forward whirl 0.15 Typical of system with material 0.1 damping. 0.05 Critical speeds 0 0. 10000. 20000. 30000. 40000. 50000. Rotor speed [rpm] 9
Rotordynamic tests at room temperature In-phase imbalances Out of phase imbalances 240 mg ( u = 15 m) and 360 mg ( u = 22.6 m ). 10
Normalized rotor responses Drive end Horizontal 360 Room temperature tests Phase lag [deg] 240 mg Out of Phase (180 o ) Imbalance 360 mg 240 masses. Rotor response normalized with 120 respect to the smaller imbalance mass ( 240 mg) 0 T FE T DE 0 10000 20000 30000 40000 50000 Rotor speed [rpm] T S 80 DE rotor FE rotor 240 mg Amplitude 0-pk [um] Critical speed 360 mg Normalized rotor 360 mg amplitudes show 40 system behaves ~ 240 mg linearly up to max. speed = 50 krpm ~15 m 0 0 10000 20000 30000 40000 50000 11 Rotor speed [rpm]
Predictions and test results Drive end Horizontal 360 360 Measurements Phase lag [deg] Phase lag [deg] Measurements 240 240 Predictions 120 120 Predictions 0 0 0 10000 20000 30000 40000 50000 0 10000 20000 30000 40000 50000 Rotor speed [rpm] Rotor speed [rpm] 120 120 240 mg out-of-phase 360mg out-of-phase Amplitude 0-pk [um] Amplitude 0-pk [um] Measurements 80 80 Measurements Predictions 40 40 Predictions ~15 m 0 0 0 10000 20000 30000 40000 50000 0 10000 20000 30000 40000 50000 Rotor speed [rpm] Rotor speed [rpm] 12 Predictions and measurements in good agreement
Tests with increasing heater temperature 200 C Heater temperature, Ts [ ° C] 150 C 100 C 22 C Graph does not show axial thermal gradient) Rotor and bearings heat unevenly. 13
Test cases Rotor Heater set Time # speed Temperature, T s [ºC] [min] [krpm] ~ 22 (Heater off) 100 150 200 1 0 135 ~ 22 (Heater off) 100 150 200 2 30 145 ~ 22 (Heater off) 100 150 200 3 40 150 ~ 22 (Heater off) 100 150 200 4 50 230 Cooling flow rate: 160 LPM In-phase imbalances Out of phase imbalances 240 mg ( u = 15 um) and 360 mg ( u = 22.6 um ). 14
Thermocouples location Rotor free end Heater reference Air inlet (160 LPM) T DE T FE temperature, T s Rotor drive end Rotor Heater coil MMFB MMFB T duc t Drive end Duct bearing Free end temperature T 4 T 8 bearing T 1 T 5 T 3 T 7 T 2 T 6 15
Rotor OD temperatures Rotor speed: 50 krpm T FE T DE T S DE bearing FE bearing T duct Heater off Heater off T S = 100ºC T S = 150ºC T S = 200ºC T S = 100ºC T S = 150ºC T S = 200ºC 100 40 Temperature rise [ºC] Temperature rise [ºC] 75 30 Rotor free end 50 20 Rotor 10 25 drive end 0 0 0 50 100 150 200 250 0 50 100 150 200 250 Time [min] Time [min] Rotor free and drive end temperatures Duct air temperature Rotor and duct temperatures increase with heater temperature. 16 Large axial thermal gradient, DE to FE
Bearing OD temperatures Rotor speed: 50 krpm T FE T DE T S DE bearing FE bearing Heater off Heater off T duct T S = 100ºC T S = 150ºC T S = 200ºC T S = 100ºC T S = 150ºC T S = 200ºC 40 40 Temperature rise [ºC] Temperature rise [ºC] 30 30 T 2 T 1 T 7 T 6 T 4 T 8 T 5 T 3 20 20 T 4 T 8 10 T 1 T 3 T 5 10 T 7 T 2 T 6 0 0 0 50 100 150 200 250 0 50 100 150 200 250 Time [min] Time [min] FE bearing temperatures ( T 1 -T 4 ) DE bearing temperatures ( T 5 -T 8 ) Bearings show similar temperatures. The cooling air supply (~160 L/min) maintains low bearing temperatures 17
Rotor temperatures & rotor speed increase Heater at 200 ° C Rotor Temperature [ ° C] T 4 T 1 Heat flows from coil while rotor T 3 Thermocouples spins from 0 to 50 krpm on bearings OD T 2 At any fixed heater temperature, the rotor temperature increases with time (until thermal equilibrium) 18
Rotor OD temperature rises Rotor speeds: 0-50 krpm T FE T DE Heater temperature: 22- 200 o C T S DE bearing FE bearing T duct 100 100 Heater off Ts=100 ºC Heater off Ts=100 ºC Ts=150 ºC Ts=200 ºC Temperature rise [ºC] Temperature rise [ºC] Ts=150 ºC Ts=200 ºC 80 80 200 ºC 60 60 150 ºC 200 ºC 40 100 ºC 40 150 ºC 100 ºC 20 Heater off 20 Heater off 0 0 0 10 20 30 40 50 0 10 20 30 40 50 Rotor speed [krpm] Rotor speed [krpm] Rotor FE temperature ( T FE ) Rotor DE temperature ( T DE ) Due to the heater thermal gradient, rotor free end is 19 hotter than drive end
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