Measurements of Rotordynamic Response in a High temperature Rotor - - PowerPoint PPT Presentation

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Measurements of Rotordynamic Response in a High temperature Rotor Supported on Two Metal Mesh Foil Bearings

32nd Turbomachinery Research Consortium Meeting

TRC-BC001-12

Luis San Andrés Mast-Childs Professor Thomas Abraham Chirathadam Research Assistant

TRC Project 32513/1519FB

May 2012

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Metal Mesh Foil Bearing (MMFB)

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 WHY METAL MESH ?

Bearing cartridge Compressed metal mesh pads Heat treated top foil (Inner surface coated with MoS2) Bearing cartridge Compressed metal mesh pads Heat treated top foil (Inner surface coated with MoS2)

• Large hysteresis damping.
• Wide temperature range
• Damping unaffected by

soaking in oil

• Empirical model available

(Vance et al., 2000-2005)

• Hybrid gas bearings with

metal mesh improves

• verall performance.
• Enhanced damping

without compromising stiffness.

• Static load does not affect

damping

• Shape memory alloys

(expensive) gives + damping as excitation amplitude grows (Ertas et al., 2008-20010)

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Objective: Demonstrate high temperature reliable

• peration 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

TRC project (1 year)

Metal Mesh Foil Bearing

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TRC Budget

$ 38,557

$ 3,200 Supplies for test rig and construction of test bearings $ 10,138 Tuition three semesters ($3,488 x 3) $ 1,200 Travel to (US) technical conference $ 2,419 Fringe benefits (0.6%) and medical insurance ($191/month) $ 21,600 Support for graduate student (20 h/week) x $ 1,700 x 12 months

Year I

Research will characterize, qualitatively and quantitatively, MMFBs of low cost, simple in construction, and suited for high temperature

• peration. The work is important for turbochargers,

turboexpanders and microgas turbines

Metal Mesh Foil Bearings

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• 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)

Test rotor Motor driving the rotor MMFB

Test rotor Eddy current sensor MMFB End cap holding bearing

Test rig for high temperature tests

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MMFB components

Metal mesh pads

Compressed weave of copper wires Compactness (density)=20%

Simple to manufacture and assemble 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 pads and top foil inserted inside bearing cartridge. Top foil firmly affixed in a thin slot made with wire-EDM machining

Stiffness and damping of MMFB depend on metal mesh compactness

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Dimensions: rotor and bearings

Rotor Inconel 718 Mass, M 1.36 kg Length 200.7 mm Inner diameter, Di 17.90 mm Outer diameter, DO 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 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 Top foil thickness 0.12 mm Top foil (Chrome Nickel steel alloy) Hardness Rockwell (40/45) Radial clearance based on geometry

0.035 mm

MMFB with 4 pads Cooling air flow rate 160 LPM

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Predicted MMFB force coefficients

Predictive (in-house) tool models metal mesh pad as a uniform stiffness layer beneath the elastic top foil

• 0.4
• 0.2

0.0 0.2 0.4 0.6 0.8 1.0 1.2 10 20 30 40 50 60

rotor speed (krpm) Stiffnesses [MN/m]

Kxx KXY KYX KYY

K XX K YY K XY K YX

Drive end bearing (DEB). Static load = 7.4 N

• 0.3
• 0.2
• 0.1

0.0 0.1 0.2 0.3 0.4 10 20 30 40 50 60

rotor speed (krpm) Damping [kN.s/m]

Cxx CXY CYX CYY

C XX C YY C XY C YX

Drive end bearing (DEB). Static load = 7.4 N

X Y W

Stiffness Damping

Direct stiffness increases 80% with speed. Damping drops! Small cross-K’s

Drive end bearing

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Critical speeds and damping ratios

16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1

• 0.06
• 0.04
• 0.02

0.02 0.04 0.04 0.08 0.12 0.16 0.2 0.24 Axial Location [m] Shaft Radius [m]

MMFB supports Flexible coupling Coupling added mass and inertia MMFBs Imbalance planes

DRIVE END FREE END

Rotor 10000 20000 30000 40000 50000 0. 10000. 20000. 30000. 40000. 50000. Natural frequency [rpm] Rotor speed [rpm] 0.05 0.1 0.15 0.2 0.25 0.3 0. 10000. 20000. 30000. 40000. 50000. Damping ratio Rotor speed [rpm]

Conical forward whirl Cylindrical forward whirl Critical speeds

Critical speeds < 10 krpm b/c bearings are soft. Rigid rotor modes: conical and cylindrical. Damping decreases with speed. Typical of system with material damping. Model rotor-bearing system

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Rotordynamic tests at room temperature

In-phase imbalances Out of phase imbalances 240 mg (u = 15 m) and 360 mg (u = 22.6 m ).

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Normalized rotor amplitudes show system behaves ~ linearly up to max. speed = 50 krpm

Normalized rotor responses

40 80 10000 20000 30000 40000 50000 Rotor speed [rpm] Amplitude 0-pk [um]

240 mg 360 mg

120 240 360 10000 20000 30000 40000 50000 Rotor speed [rpm] Phase lag [deg]

Out of Phase (180o) Imbalance masses. Rotor response normalized with respect to the smaller imbalance mass ( 240 mg)

240 mg 360 mg 240 mg 360 mg Critical speed

~15 m

Room temperature tests Drive end Horizontal

TFE TDE TS

FE rotor DE rotor

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Predictions and measurements in good agreement

Predictions and test results

40 80 120 10000 20000 30000 40000 50000 Rotor speed [rpm] Amplitude 0-pk [um]

120 240 360 10000 20000 30000 40000 50000 Rotor speed [rpm] Phase lag [deg]

120 240 360 10000 20000 30000 40000 50000 Rotor speed [rpm] Phase lag [deg] 40 80 120 10000 20000 30000 40000 50000 Rotor speed [rpm] Amplitude 0-pk [um]

Predictions Measurements ~15 m Predictions Measurements Predictions Measurements Predictions Measurements

240 mg out-of-phase 360mg out-of-phase Drive end Horizontal

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Rotor and bearings heat unevenly.

Tests with increasing heater temperature

Graph does not show axial thermal gradient) Heater temperature, Ts [°C]

200 C 22 C 150 C 100 C

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Test cases

230 50 ~ 22 (Heater off) 100150200 4 150 40 ~ 22 (Heater off) 100150200 3 145 30 ~ 22 (Heater off) 100150200 2 135 ~ 22 (Heater off) 100150200 1 Time [min] Rotor speed [krpm] Heater set Temperature, Ts [ºC] #

In-phase imbalances Out of phase imbalances 240 mg (u = 15 um) and 360 mg (u = 22.6 um ). Cooling flow rate: 160 LPM

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Thermocouples location

TFE TDE

Free end bearing Drive end bearing

Heater coil

Rotor T4 T1 T2 T3 T8 T5 T6 T7

Rotor drive end Rotor free end

MMFB

Heater reference temperature, Ts Tduct Duct temperature

MMFB

Air inlet (160 LPM)

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Rotor and duct temperatures increase with heater temperature. Large axial thermal gradient, DE to FE

Rotor OD temperatures

Rotor speed: 50 krpm 10 20 30 40 50 100 150 200 250

Time [min] Temperature rise [ºC]

25 50 75 100 50 100 150 200 250

Time [min] Temperature rise [ºC]

Rotor free end Rotor drive end

Rotor free and drive end temperatures Duct air temperature

TS=100ºC TS=150ºC TS=200ºC Heater off TS=100ºC TS=150ºC TS=200ºC Heater off

Tduct

TFE TDE TS

FE bearing DE bearing

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Bearings show similar temperatures. The cooling air supply (~160 L/min) maintains low bearing temperatures

Bearing OD temperatures

FE bearing temperatures (T1-T4)

TS=100ºC TS=150ºC TS=200ºC Heater off TS=100ºC TS=150ºC TS=200ºC Heater off

10 20 30 40 50 100 150 200 250

Time [min] Temperature rise [ºC]

DE bearing temperatures (T5-T8)

10 20 30 40 50 100 150 200 250

Time [min] Temperature rise [ºC]

T4 T1 T2 T3 T8 T7 T6 T5

T2 T1 T4 T3 T7

T6 T8 T5

Rotor speed: 50 krpm

Tduct

TFE TDE TS

FE bearing DE bearing

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At any fixed heater temperature, the rotor temperature increases with time (until thermal equilibrium)

Rotor temperatures & rotor speed increase

Rotor Temperature [°C] Heater at 200 °C

T4 T1 T2 T3

Thermocouples

• n bearings OD

Heat flows from coil while rotor spins from 0 to 50 krpm

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Due to the heater thermal gradient, rotor free end is hotter than drive end

Rotor OD temperature rises

Rotor speeds: 0-50 krpm

20 40 60 80 100 10 20 30 40 50 Rotor speed [krpm] Temperature rise [ºC]

Heater off Ts=100 ºC Ts=150 ºC Ts=200 ºC

20 40 60 80 100 10 20 30 40 50 Rotor speed [krpm] Temperature rise [ºC]

Heater off Ts=100 ºC Ts=150 ºC Ts=200 ºC

Heater temperature: 22- 200 oC Rotor FE temperature (TFE) Rotor DE temperature (TDE)

200 ºC 150 ºC 100 ºC Heater off Heater off 100 ºC 150 ºC 200 ºC

Tduct

TFE TDE TS

FE bearing DE bearing

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Bearing temperatures increase with rotor speed and are impervious to rotor thermal gradient. Supply air flow at ~ 160 L/min cools the bearings

Bearing OD temperature rises

FE bearing temperature (T1-4) DE bearing temperature (T5-8)

10 20 30 40 10 20 30 40 50 Rotor speed [krpm] Temperature rise [ºC]

Heater off Ts=100 ºC Ts=150 ºC Ts=200 ºC

10 20 30 40 10 20 30 40 50 Rotor speed [krpm] Temperature rise [ºC]

Heater off Ts=100 ºC Ts=150 ºC Ts=200 ºC 200 ºC 150 ºC 100 ºC Heater off Heater off 100 ºC 150 ºC 200 ºC

Rotor speeds: 0-50 krpm Heater temperature: 22- 200 oC

Tduct

TFE TDE TS

FE bearing DE bearing

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Rotor responses at various temperatures are similar. No clear trend

Rotor response at increasing temperatures

Out of Phase imbalance masses = 240 mg. Large remnant rotor imbalance. Rotor free end horizontal

• response. Runout at ~2.3 krpm

180 360 10000 20000 30000 Rotor speed [rpm] Phase lag Heater off 100 C 150 C 200 C 50 100 150 200 10000 20000 30000 Rotor speed [rpm] Amplitude [m 0-p] Heater off 100 C 150 C 200 C

Ts=22 ºC Ts=100 ºC Ts=150 ºC Ts=200 ºC Heater set Ts (ºC) 22 100 150 200 Rotor FE TFE (ºC) 26 47 63 82

TFE TDE TS

FE rotor DE rotor

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Idem

Heater set Ts (ºC) 22 100 150 200 Rotor DE TDE (ºC) 26 36 46 54

180 360 10000 20000 30000 Rotor speed [rpm] Phase lag Heater off 100 C 150 C 200 C

50 100 150 200 10000 20000 30000 Rotor speed [rpm] Amplitude [m 0-p] Heater off 100 C 150 C 200 C

Ts=22 ºC Ts=100 ºC Ts=150 ºC Ts=200 ºC

Out of Phase imbalance masses = 240 mg. Large remnant rotor imbalance. Rotor drive end horizontal

• response. Runout at ~2.3 krpm

Rotor response at increasing temperatures

TFE TDE TS

FE rotor DE rotor

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Large amplitude peaks at critical speed. Not affected by rotor temperature.

Out of Phase Imbalance masses= 240

• mg. Large remnant rotor imbalance.

Rotor drive end vertical

• response. Runout at ~2.3 krpm

Heater set Ts (ºC) 22 100 150 200 Rotor DE TDE (ºC) 26 36 46 54

180 360 10000 20000 30000 Rotor speed [rpm] Phase lag Heater off 100 C 150 C 200 C 50 100 150 200 10000 20000 30000 Rotor speed [rpm] Amplitude [m 0-p] Heater off 100 C 150 C 200 C

Ts=22 ºC Ts=100 ºC Ts=150 ºC Ts=200 ºC

Rotor response at increasing temperatures

TFE TDE TS

FE rotor DE rotor

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Evidence of small amplitude sub synchronous whirl with hottest rotor

(Rotor DE temp increases from 24oC to 62oC)

Synchronous response is dominant.

Waterfalls of rotor motions

Rotor drive end vertical

50 100 150 200 250 300 200 400 600 800 1000 Frequency [Hz] Amplitude [ m 0-pk]

Heater off

Subsynchronous 2X 1X Rotor avg.

• temp. = 24 ºC

0 rpm 36 krpm 3X 50 100 150 200 250 300 200 400 600 800 1000 Frequency [Hz] Amplitude [ m 0-pk]

Heater Ts=200 ºC

1X 2X Subsynchronous Rotor avg.

• temp. = 78 ºC

36 krpm 0 rpm 3X

In phase imbalance masses= 360 mg

TFE TDE TS

FE rotor DE rotor

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Conclusions

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 50 krpm. c) Most rotor responses do not show significant different between cold (room) and high temperature. d) With sufficient cooling air ~ 160 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 reinforced need of air supply for

adequate thermal management.

TFE TDE TS

FE rotor DE rotor

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Questions ?

For more information http://rotorlab.tamu.edu