MEASUREMENTS OF ROTORDYNAMIC ROTOR SUPPORTED ON METAL MESH

Transcription

1 ASME Turbo Expo 213 GT213 June 3-7, 213, San Antonio, Texas, USA MEASUREMENTS OF ROTORDYNAMIC RESPONSE AND TEMPERATURES IN A ROTOR SUPPORTED ON METAL MESH FOIL BEARINGS Thomas Chirathadam Southwest Research Institute, San Antonio, TX Luis San Andrés ASME Paper GT Fellow ASME Texas A&M University accepted for journal publication This material is based upon work supported by the TAMU Turbomachinery Research Consortium and Prof. Luis San Andrés incentive fund

2 Oil-free systems for a sustainable future Significant reduction in CO 2 emissions. Improved operating limits (temperature, caustic environment etc.) Distributed power generation (eg: Fuel cell turbo generator) Environmentally friendly. Higher energy efficiency Compact high efficiency units. High speed/high temperature operations Power generation for hybrid propulsion High-efficiency oil-free gas turbine (max 1 kw) Source: 2

3 Oil-free bearings: applications Pros: Cons: Low drag, reduced cost, long term benefits Low load capacity + system level redesign Turbine Gas Bearings Spacer ring Cooling air inlet Compressor Journal Air outlet Oil-free turbocharger Modified center housing Turbo-generator ( Fuel cell hybrid) Power: 1 MW Ref.: 3

4 Metal Mesh Foil Bearing (MMFB) MMFB COMPONENTS: bearing cartridge, metal WHY a METAL MESH? mesh ring and top Foil Large hysteresis damping. Hydrodynamic air film develops between rotating ti shaft and top foil. Wide temperature range Empirical model available (Vance et al.,2-25) MMFB assembly Hybrid gas bearings Enhanced damping without compromising stiffness. Applied static load does not affect damping Shape memory alloys (expensive) shows increasing damping with excitation amplitudes Top foil: Preformed heat treated steel strip (Ertas et al.,28-21) Metal mesh: Compressed Copper wires (2-3%) 4

5 Bearing components MMFB Bump type FB Top Foil Metal mesh pad Bearing cartridge (+top foil+ metal mesh) Top Foil Bump foil Bearing cartridge (+top foil+ bump foil)

6 Past work: Metal mesh foil bearings (28-211) San Andrés et al. (21) J. Eng. Gas Turb. & Power, 132(3) Assembled first prototype MMFB (L=D=28 mm). Load vs Deflection shows large structural damping.7). Frequency dependent stiffness agrees with predictions. San Andrés et al. (29) ASME GT Demonstrated operation to 45 krpm with early rotor lift off. Educated d undergraduate d students. San Andrés et al. (21) J. Eng. Gas Turb. & Power, 132 Start and shut down to measure torque and lift-off speed. Low drag friction factor ~.1 at high speed 6 krpm. San Andrés and Chirathadam (211) J. Eng. Gas Turb. & Power, 133 Rotordynamic coefficients from unidirectional impact loads. Estimated stiffness and damping force coefficients at 5 krpm. 6

7 Past work: metal mesh foil bearings (29-21) San Andrés et al. (29) ASME GT San Andrés et al. (21) J. Eng. Gas Turb. & Power, 132 Drag torque & shaft lift-off speed from rotor start up and shut down tests. Low drag friction factor f ~.1 at high speed 6 krpm. Mixed lubrication Power loss s [W] Increasing static load (W s ) to 35.6 N (8 lb) Dead weight (W D = 3.6 N) Load 8.9 N Load 17.8 N Load d267n 26.7 Load 35.6 N Hydrodynamic lubrication 35.6 N (8 lb) 26.7 N (6 lb) 17.8 N (4 lb) 8.9 N (2 lb) 1 5 Rotor accelerates Journal speed [rpm] 7

8 Past work: Metal mesh foil bearings San Andrés and Chirathadam (211) J. Eng. Gas Turb. & Power, 133 (212) Identification of rotordynamic coefficients using two e- shakers for rotor speeds (4-5 krpm), displacement amplitudes ( 2-3um), static load ( N). Estimated loss factor ~1 San Andrés and Chirathadam (212) 2 GT Comparison of static and dynamic 1.5 performance of similar size MMFB and Generation I bump foil bearing (BFB). MMFB 1 shows 2-3 times BFB damping. Airborne drag friction factor ~.33 for both bearings 5.5 Loss factor [-] rpm-22n 4 krpm-22n 45 krpm-22n 5 krpm-22n 5 krpm-36n Frequency [Hz] 8

9 Test rig for high temperature tests Test rotor Motor driving the rotor End cap holding bearing MMFB MMFB Eddy current sensor Test rotor Max. rotor speed 5 krpm Coil heater warms hollow rotor from inside (max 3 C). Imbalance masses added at two ends of rotor (in phase & out of phase) 9

10 Dimensions: rotor and bearings Rotor Inconel 718 Mass, M Length Inner diameter, D i Outer diameter, D O Rotor diameter at bearings Bearing span 1.36 kg 2.7 mm 17.9 mm mm mm 13 mm Bearings Cartridge outer diameter Cartridge inner diameter Inner diameter, D Axial length, L Copper mesh pad thickness 5.8 mm 42. mm mm 38.1 mm 2.6 mm MMFB with 4 pads Cooling air flow rate 16 LPM mesh hdensity (compactness) 3 % Wire diameter (mm).3 Number of metal mesh pads 4 Top foil thickness 12mm.12 Top foil (Chrome Nickel steel alloy) Hardness Rockwell (4/45) Radial clearance based on geometry.35 mm 1

11 MMFB components Simple to manufacture and assemble Top Foil mm top foil Chrome-Nickel alloy Rockwell 4/45 Heat treated at ~ 45 ºC for 4 hours and allowed to cool. Foil retains arc shape after heat treatment Sprayed with MoS 2 sacrificial coating Metal mesh pads Compressed weave of copper wires Compactness (density)=2% Stiffness and damping of MMFB depend d on metal mesh compactness Bearing cartridge (+top foil+ metal mesh) Metal mesh pads and top foil inserted inside bearing cartridge. Top foil firmly affixed in a thin slot made with wire-edm machining 11

12 Predicted MMFB force coefficients Predictive (in-house) tool models metal mesh pad as a uniform stiffness layer beneath the elastic top foil X W Drive end bearing Y ses [MN/m] Stiffnes Stiffness K XX K YY Kxx KXY KYX KYY K YX K XY Drive end bearing (DEB). Static load = 7.4 N rotor speed (krpm) g [kn.s/m] Dampin C YY C XX C YX Cxx Damping CXY CYX CYY C XY Drive end bearing (DEB). Static load = 7.4 N rotor speed (krpm) Direct stiffness increases 8% with speed. Damping drops! Small cross-k s 12

13 Critical speeds and damping ratios Shaft Radiu us [m] Coupling added mass and inertia DRIVE END 7 8 Flexible coupling Imbalance planes Rotor MMFBs 12 MMFB supports FREE END Axial Location [m].3 Model rotor-bearing system 16 Natural frequ uency [rpm] Critical speeds < 1 krpm b/c bearings are soft. Rigid rotor modes: conical and cylindrical. forward backward f=638.8 cpm d=.1287 zeta N=1 rpm forward backward f= cpm d=.191 zeta N=1 rpm Rotor speed [rpm] Damping ra atio Conical forward whirl Critical speeds Cylindrical forward whirl Rotor speed [rpm] Damping decreases with speed. Typical of system with material structural damping. 13

14 Rotordynamic tests at room temperature In-phase imbalances Out of phase imbalances 24 mg g( (u = 15 m) ) and 36 mg (u = 22.6 m ). 14

15 Normalized rotor responses Phas se lag [deg] Amplitu ude -pk [um m] mg 36 mg Rotor speed [rpm] Critical speed 36 mg 24 mg 24 mg 36 mg Rotor speed [rpm] ~15 m Drive end Horizontal Room temperature tests Out of Phase (18 o ) Imbalance masses. Rotor response normalized with respect to the smaller imbalance mass ( 24 mg) T S T FE FE rotor DE rotor T DE Normalized rotor amplitudes show system behaves ~ linearly up to max. speed = 5 krpm 15

16 Predictions and test results Drive end Horizontal Phas se lag [deg] Measurements Predictions Pha ase lag [deg] Measurements Predictions Amp plitude -pk [um m] Rotor speed [rpm] Rotor speed [rpm] 24 mg out-of-phase 36mg out-of-phase Measurements Predictions ~15 m Ampl litude -pk [um m] 12 Measurements 8 Predictions Rotor speed [rpm] Predictions and measurements are in agreement Rotor speed [rpm] 5 16

17 About thermal management in GFBs

18 Prior art: thermal management in GFBs Heshmat et al (25): Demonstrates hot (65C) GFB operation in a turbojet engine to 6 krpm. Cooling flow rates up to 57 L/min shows large axial thermal gradients (13ºC/cm) LaRue et al (26): Oil-free Turbocharger. Airflow cools TC rotor, GFB. Lubell et al (26): In an oil-free micro-turbine, air flow through hollow rotor axis show rapid rotor temperature drop. Dykas (26): In foil thrust bearings, cooling flow rates to 45 L/min increase bearing load capacity at high rotor speeds. Radil et al (27): Cooling methods (axial cooling, direct and indirect shaft cooling) for thermal management in a hot GFB environment San Andrés et al (29): Forced cooling flow effective at high rotor temperatures, but limited effectiveness at low rotor temperatures Ryu (21): Comprehensive measurements of GFB temperature and Ryu (21): Comprehensive measurements of GFB temperature and rotordynamic response. Forced cooling flows do not affect rotor response amplitude and vibration frequencies. 18

19 Tests with increasing heater temperature 2 C Heate r tempera ature, Ts [ C] 15 C 1 C 22 C Cooling air flow rate 16 LPM Graph does not show axial thermal gradient) Rotor and bearings heat unevenly. 19

20 Thermocouples location Heater reference temperature, T s Rotor free end T FE Air inlet (16 LPM) T DE Rotor drive end Rotor Heater coil MMFB MMFB Free end bearing T duct Duct temperature T 4 T 8 Drive end bearing Thermocouple e (Bearing mid-span) T 1 T 3 T 5 T 7 T 2 T 6 2

21 Thermocouples in bearing housings Duct Thermocouple inside duct Rotor free end (FE) Rotor drive end (DE) Bearing housing T out Bearing support housing Heater Rotor (free end) 21

22 Test cases # Heater set Temperature, T s [ºC] Rotor speed [krpm] Time [min] 1 ~ 22 (Heater off) ~ 22 (Heater off) ~ 22 (Heater off) ~ 22 (Heater off) Cooling flow rate: 16 LPM In-phase imbalances Out of phase imbalances 24 mg (u = 15 um) and 36 mg (u = 22.6 um ). 22

23 Rotor OD temperatures Rotor speed: 5 krpm T S T FE T DE Temp perature ris se [ºC] Heater off FE bearing T S =1ºC T S =15ºC T S =2ºC Rotor free end Rotor drive end Time [min] T duct Rotor free and drive end temperatures DE bearing rise [ºC] Tempe erature Heater off T S =1ºC T S =15ºC T S =2ºC Time [min] Duct air temperature Rotor and duct temperatures increase with heater temperature. Large axial thermal gradient from DE to FE 23

24 Bearing OD temperatures Rotor speed: 5 krpm T FE T DE T S Te emperatur re rise [ºC C] Heater off T S =1ºC T S =15ºC T S =2ºC T 3 T 4 T 4 T 1 T 2 T 1 T 3 Time [min] FE bearing temperatures (T 1 -T 4 ) re rise [ºC C] Te emperatu FE bearing DE bearing T Heater off duct T S =1ºC T S =15ºC T S =2ºC T 2 T T 5 T 5 T 8 T 8 T 6 T 7 T 7 Time [min] DE bearing temperatures (T 5 -T 8 ) Bearings show similar temperatures. Cooling air supply (~16 L/min) maintains low bearing temperatures. 24

25 Rotor temperature & rotor speed increase [ C] Rotor Temperature Heater at 2 C Cooling air flow rate 16 LPM T 4 Heat flows from coil while rotor spins from to 5 krpm T 1 T 3 Thermocouples on bearings OD T 2 At any fixed heater temperature, the rotor temperature increases with time (until thermal equilibrium). 25

26 Rotor OD temperature rise Rotor speed: -5 krpm T S T FE T DE Heater temperature: 22-2 o C FE bearing T duct DE bearing ise [ºC] Temp perature r Heater off Ts=1 ºC Ts=15 ºC Ts=2 ºC 2 ºC 15 ºC 1 ºC Heater off Rotor speed [krpm] erature ris se [ºC] Temp Heater off Ts=1 ºC Ts=15 ºC Ts=2 ºC 2 ºC 15 ºC 1 ºC Heater off Rotor speed [krpm] Rotor FE temperature (T FE ) Rotor DE temperature (T DE ) Due to the heater thermal gradient, rotor free end is hotter than drive end. 26

27 Bearing OD temperature rise Rotor speed: -5 krpm Heater temperature: 22-2 o C T S T FE T DE re rise [ºC] Temperatu 4 Heater off Ts=1 ºC Ts=15 ºC Ts=2 ºC 2 ºC 15 ºC 1 ºC Heater off FE bearing Rotor speed [krpm] T duct ] Temperatu ure rise [ºC DE bearing Heater off Ts=1 ºC Ts=15 ºC Ts=2 ºC 2 ºC 15 ºC 1 ºC Heater off Rotor speed [krpm] FE bearing temperature (T 1-4 ) DE bearing temperature (T 5-8 ) Bearing temperatures increase with rotor speed and are impervious to rotor thermal gradient. Supply air flow at ~ 16 L/min cools the bearings. 27

28 Rotor response at increasing temperatures Phase l ag Heater off 1 C 15 C 2 C Drive end horizontal plane. Out of Phase imbalance mass 24 mg Runout at ~2.3 krpm Amplitude [ m -p] Rotor speed [rpm] Ts=1 C Ts=15 C Ts=2 C Heater off 1 C 15 C 2 C Rotor speed [rpm] T FE T DE T S FE rotor DE rotor Heater set T s (ºC) Rotor DE T DE (ºC) Rotor responses at various temperatures are similar. No clear trend. 28

29 Rotor response at increasing temperatures Phase lag Heater off 1 C 15 C 2 C Rotor speed [rpm] Drive end vertical plane. Out of Phase imbalance mass 24 mg Runout at ~2.3 krpm T FE T DE T S FE rotor DE rotor [ m -p] Amplitude Ts=2 C Ts=1 C Ts=15 C Heater off 1 C 15 C 2 C Heater set T s (ºC) Rotor DE T DE (ºC) Idem Rotor speed [rpm] 29

30 Waterfalls of rotor response Drive end vertical Amplitude [ m -pk] Amp plitude [ m -pk k] 3 In phase imbalance mass= 36 mg Subsynchronous 1X 2X 3X Rotor avg. temp. = 24 ºC Heater off Frequency [Hz] Subsynchronous 1X 2X 3X Rotor avg. temp. = 78 ºC Heater T s =2 ºC Frequency [Hz] rpm 36 krpm rpm 36 krpm T S T FE FE rotor DE rotor T DE Very small amplitude sub synchronous whirl with hottest rotor (Rotor DE temp increases from 24 o C to 62 o C) Synchronous response is 3 dominant.

31 Conclusions ASME Paper GT a) At room temperature, rotor response predictions and measurements are in agreement. Measurements show bearings have low damping. b) Rotor-bearing system behaves linearly up to 5 krpm. c) Most rotor responses do not show significant different between cold (room) and high temperature. d) With sufficient cooling air ~ 16 L/min, the bearings performance is not affected by rotor temperature f) Prior TAMU work showed the importance of cooling air flow. The current tests reinforce the need of an adequate air supply for efficient i thermal management. 31

32 Acknowledgments/Thanks to Honeywell Turbocharging Technologies Korean Institute of Science and Technology Turbomachinery Research Consortium Questions (?) For more information ASME Paper GT

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34 High temperature measurements Rotor at rest T S =1ºC T S =15ºC T S =2ºC T S =1ºC T S =15ºC T S =2ºC T FE,DE -T [ºC] Tem mperature rise, 1 75 Free end 5 25 Drive end Time [min] Free end (T FE ) and drive end (T DE ) Te emperature rise e, T duct -T [ºC] Time [min] Duct air temperature (T duct ) T S T FE FE bearing T duct T DE DE bearing Temp perature rise, T 1-4 -T [ºC] T S =1º 4C 3 T 4 T 1 T 3 T S =15ºC T S =2ºC T S =1º 4 C perature rise, T 5-8 -T [ºC] T 6 T 2 2 T 2 2 T 1 1 T 3 T Time [min] Tem 3 1 T 5 T 8 T S =15ºC T S =2ºC T 7 T 7 T 6 T 8 T Time [min] 34 Free end bearing sleeve (T 1 -T 4 ) Drive end bearing sleeve (T 5 -T 8 )