current developments in gas bearings for microturbomachinery...

Current Developments in Gas Bearings for

Microturbomachinery

CIBIM 88th Congreso Iberoamericano de Ingenieria Mecancia

Cusco-Peru

Turbomachinery Laboratory, Texas A&M University Mechanical Engineering Department

Luis San Andrés Mast-Childs Professor

October 2007

MICROTURBOMACHINERYMICROTURBOMACHINERY

Justification

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.

Meso-scale or MEMS turbomachinery (< 100W) forNext Generation Land Warriors, Micro vehicles & robots, Portable electronic devices and systems, Smart munitions

MICROTURBOMACHINERYMICROTURBOMACHINERY as per IGTIas per IGTI

ASME Paper No. GT2002-30404

Honeywell, Hydrogen and Fuel Cells Merit Review

Automotive turbochargers, turbo expanders, compressors,

Distributed power(Hybrid Gas turbine & Fuel Cell), Hybrid vehicles

Drivers:deregulation in distributed power, environmental needs, increased reliability & efficiency

International Gas Turbine Institute

Max. Power ~ 250 kWatt

MTM POWER RANGEMTM POWER RANGE

< 100 Watt

http://smarteconomy.typepad.com/smart_economy/2006/09/microgas_turbin.html

Kang, S., Ph D dissertation (Stanford Univ.)

Portable Electronic Devices

< 250 kWatt

http://www.grc.nasa.gov/WWW/Oilfree/turbocharger.htm

http://www.miti.cc/newsletters/150hpcompressozr.pdf

ASME Paper No. GT2002-30404

Honeywell, Hydrogen and Fuel Cells Merit Review

Auto engine and part / Industrial compressor

Distribute power(Gas turbine &Fuel Cell Hybrid)

Industrial applications (30 kW Industrial applications (30 kW –– 1 MW)1 MW)

Aircraft Gas Turbine Engines

Compressor Air Cycle Machine

Turbojet Engines

source: www.miti.cc

Industrial applicationsIndustrial applications

Auxiliary Power Units

Turbocharger

Turboexpander

Turbopumps

source: www.miti.cc

Capstone’s C30 Engine

Diffuser

Compressor

Turbine Nozzle

Turbine

Oil-Free Radial Bearing

Oil-Free Thrust BearingThrust Runner

Oil-Free Foil Bearings:

>500°CProprietary bearing design and coating

Thin Dense Chrome journals

1.4 MDN (idle)3.1 MDN (full speed)

~1.5 L/D1.6 psi static load

Demonstrated Life: >40k hours; >6k

cycles and over 11 Mhrs field life

source: Dan Lubell, 2006 IJTC, Capstone Turbine Corportation

MICRO GASMICRO GAS TURBINESTURBINES

100Turbec, ABB & Volvo

70, 250IngersollRand

175General Electric

35, 60, 80, 150Elliott EnergySystems

30, 60, 200Capstone

25, 80Bowman

OUTPUT POWER (kW)MANUFACTURER

Microturbine Power Conversion Technology Review, ORNL/TM-2003/74.

Cogeneration systems with high efficiency• Multiple fuels (best if free)• 99.99X% Reliability• Low emissions• Reduced maintenance• Lower lifecycle cost

Hybrid System : MGT with Fuel Cell can reach efficiency > 60%Ideal to replace reciprocating

engines. Low footprint desirable

60kW MGT


Capstone MicroTurbine™

Combustionchamber

Exhaust output

Recuperator

Fuel injector

Air bearings

Compressor

Generator

Air intake

Cooling fins

Turbine

No gearbox or other No gearbox or other mechanicalsmechanicals

Low scheduled Low scheduled maintenancemaintenance

OOnly one moving nly one moving partpart

No coolants or No coolants or lubricantslubricants

ContaminantContaminant--free free exhaustexhaust

Compact and Compact and lightweightlightweight

SuperSuper--low CO & low CO & NONOXX


MTM Expectations & Requirements

• Low cost – driven by materials• Low maintenance – driven by design• Long life – defined by the bearings

and materials• Efficient – driven by design• Fully integrated solutions – system

design


Differences between MTM & Aero engine

• Power density is less important than cost• Low pressure ratios work well with

recuperators• Efficiency is important to compete

against alternate technologies• Maintenance infrastructure is not as

prolific within customer infrastructures, making low maintenance very important


ULTRA MICROTURBOMACHINERYULTRA MICROTURBOMACHINERY

MEMS MTM

GT-2003-38866

Meso-scale MTM

2007, Journal of Micromechanics and Microengineering, Vol.17

• Palm-size power source• Brayton cycle• Gas foil bearings

www.m-dot.com

Small unmanned vehicles and to replace batteries in portable electronic devices 100 Watt & less

• Silicon wafer• 1.2 Million rpm• Thrust 0.1 N• Spiral groove and hydrostatic gas bearings

5

50

500

0.5

5000

10 100001000100

LiSO2 Battery (BA5590)

Solar Cell

Micro Solar Cell

SIZE (cm3)

POW

ER D

ENSI

TY (M

W/m

3)

Large Scale Combustor

Micro Reactor

Micro-Lithium Battery

http://ubisa.kist.re.kr/Teams/ubisa/mems.htm

http://www.robhaz.com/

RescueRobot

http://www2.northerntool.com/product/448_448.htm

Portable Generator

http://www.notebookreview.com/http://www.wir

efly.com/

Mobile electronic equipment

Large Scale Combustor

http://www.uavpayloads.com/products.php4

UAV

Micro Gas Turbine

http://www.m-dot.com/page8.html

Applications of Applications of MesoMeso/MEMS MTM/MEMS MTM

MEMS MTMMEMS MTM at MITat MIT

Source: GT2003-38866

Thrust: 11g (17 watts)

Turbine inlet temp: 1600 K

Fuel burn: 16 gram/hr

Rotor Speed: 1.2 M rpm

Weight: 2 grams

Exhaust gas temp: 1243 K

~1997: DARPA – M-Dot project

MesoscaleMesoscale MTMMTM at Stanfordat Stanford

Replace the inlet nozzle to improve specific thrust density.· Inlet nozzle: major ceramic part. Tested in 1,250°C gas· 7% performance (thrust/weight)improvement expected· Ceramic turbine built but not tested.

M-DOT micro-turbine engine

Silicon nitride inlet nozzle and turbine

Palm size gas turbine engine (thrust type)φ25 mm turbine, 400k rpmAll metal componentsRan a few minutes. Turbine blades melted!

1998: DARPA – M-Dot – Stanford – Carnegie Mellon project

Figures and text: Kang, S.,2001, Ph.D dissertation, Stanford Univ.& Personal communication with Kang, S.

• Oil-Free • NO DN limit• Low friction and power loss• Thermal management

GAS BEARINGS

AIAA-2004-5720-984

Gas Foil Bearing

GT 2004-53621

Flexure Pivot Bearing

AIAA 2004-4189

Rolling element bearings

PowerMEMS 2003

• Low temperatures• Low DN limit (< 2 M)• Need lubrication system

NICH Center, Tohoku University

Herringbone grooved bearing

• Precision fabrication process• Low load capacity and stiffness and little damping

Available Bearing TechnologiesAvailable Bearing Technologies

Largest power to weight ratio, Compact & low # of parts

Reliability and efficiency,Low maintenance

Extreme temperature and pressure

Environmentally safe (low emissions)

Lower lifecycle cost ($ kW)

High speed

Materials

Manufacturing

Processes & Cycles

Fuels

Rotordynamics & (Oil-free) Bearings & Sealing

Coatings: surface conditioning for low friction and wearCeramic rotors and components

Automated agile processesCost & number

Low-NOx combustors for liquid & gas fuelsTH scaling (low Reynolds #)

Best if free (bio-fuels)

MTM – Needs, Hurdles & Issues

Dr. Luis San AndresMast-Childs Professor

October 2007

Foil Gas Bearings for Microturbomachinery

CIBIM 88th Congreso Iberoamericano de Ingenieria Mecancia

Cusco-Peru

Gas Bearings for Oil-Free Turbomachinery• Advantages of gas-lubricated bearings over oil-

lubricated bearings for high-speed, small-scale turbomachinery– Process gas offers more cleanliness and

eliminates contamination by buffer lubricants– Gases are more stable at extreme temperature

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!Gas Bearings Must Be Simple!

Ideal gas bearings for micro turbomachinery (< 0.25 MW ) must be:

Simple – low cost, small geometry, low part count, constructed from common materials, manufactured with elementary methods.

Load Tolerant – capable of handling both normal and extreme bearing loads without compromising the integrity of the rotor system.

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) readily available

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.

• 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

Gas Foil Bearings +/-• Increased reliability: large load capacity (< 100 psi)• No lubricant supply system, i.e. reduce weight• High and low temperature capability (up to 2,500 K) • No scheduled maintenance • Ability to sustain high vibration and shock load.

Quiet operation

• Less load capacity than rolling or oil bearings• Wear during start up & shut down• No test data for rotordynamic force coefficients• Thermal management issues• Predictive models lack validation. Difficulties in

modeling complex interaction between film and foil-bumps support (dry-friction damping)

Foil Bearing Test RigFoil Bearing Test Rig

Driving motor (1HP, 50 krpm)

Flexible coupling

Optical Tachometer

Start motor(2HP, 25 krpm)

Foil bearing housing

Electromagnet loader

Test rotor

Centrifugal clutch (Engaged at ~50 krpm)

Cluth shoes

Spring

Wear ring

Ω

Shaft Diameter @ bearing locations = 1.500”

Thin dense chrome (TDC) coatingRotor mass = 2.2 lb without

couplingFree–free mode natural frequencies

= 4096 Hz and 9850 Hz

ROTOR and TEST FOIL BEARINGSROTOR and TEST FOIL BEARINGS

TOP FOILBUMP FOILS

D = 1.500”L = 1.500”

Cnominal = 1.4 mil

Foil Bearing: structural load and stiffness

Foil bearing structural load and stiffness are non linear, i.e. hardening as shaft displacement increases.

0

20

40

60

80

100

120

140

160

0 10 20 30 40 50 60

Free end bearing

Drive end bearing

2×cFE 2×cDE

Rot

or d

ispl

acem

ent (μm

)

Magnetic Load

FE Load DE Load

Bearing loads (N) 0 10 20 30 40 50 60

Bearing load (N)

160

120

80

40

0

Rot

or d

ispl

acem

ent (μm

)

0.15 0.1 0.05 0 0.05 0.1 0.15

400

200

0

200

400

FB Deflection (mm)

Stat

ic L

oad

(N)

0.2 0.15 0.1 0.05 0 0.05 0.1 0.15 0.20

1750

3500

5250

7000

FB Deflection (mm)

Stru

ctur

al S

tiffn

ess

(N/m

m)

Stat

ic L

oad

(N)

Stru

ctur

al S

tiffn

ess

(kN

/m)

FB Displacement (mm)FB Displacement (mm)

PredictionsExperimental Results

D1 = 38.10 mmθ = 45º - 225ºF ≠ K X

– Stiffness varies with deflection

Drive end

Free endYDEXDE

XFEYFE

g

Drive end

Free endYDEXDE

XFEYFE

g

WATERFALL PLOTS OF BASELINE CONDITION – no imbalance

25 krpm

2 krpm

Incipient sub sync

motions

PERFORMANCE OF SMALL ROTOR ON GAS FOIL BEARINGSPERFORMANCE OF SMALL ROTOR ON GAS FOIL BEARINGS

Waterfall plotsWaterfall plots

Amplitudes of subsynchronous

motions INCREASE as

Imbalance increases (forced

nonlinearity)


0 100 200 300 400 500 600 700 8000

20

40

60

80

100

Frequency [Hz]

Am

plitu

de [m

icro

ns]

0 100 200 300 400 500 600 700 8000

20

40

60

80

100

Frequency [Hz]

Am

plitu

de [m

icro

ns]

Dis

plac

emen

t Am

plitu

de (μ

m)

Dis

plac

emen

t Am

plitu

de (μ

m)

Frequency (Hz)

25.7 krpm

2.6 krpm u = 7.4 μm

1X 0.5X

2X

1X 0.5X

2X

8.5 krpm

25.7 krpm

2.6 krpm

12.5 krpm

20.5 krpm

u = 10.5 μm

Frequency (Hz)

Speed +

Imbalance +

Effect of imbalance on Effect of imbalance on system responsesystem response

Subsynchronous motions are most

severe from 15 krpm to 12 krpm. Super-

synchronous through critical speed

Large U

Dis

plac

emen

t Am

p. (μ

m, 0

-pk)

Synchronous component Direct component

XDE

0 3 6 9 12 150

20

40

60

80

t Am

plitu

de (μ

m)

DirectSynchronous

( , )

Dis

plac

emen

t Am

p. (μ

m, 0

-pk)


XDE

0 3 6 9 12 150

20

40

60

80

t Am

plitu

de (μ

m)

Dis

plac

emen

t Am

p. (μ

m, 0

-pk)


XDE

0 3 6 9 12 150

20

40

60

80

t Am

plitu

de (μ

m)

DirectSynchronousDirectSynchronous

( , )

D

ispl

acem

ent A

mp.

(μm

, 0-p

k) Synchronous component

Direct component XDE Imbalance mass location

FE

DE

0 3 6 9 12 150

20

40

60

80A

mpl

itude

(μm

)( , )

DirectSynchronous

D

ispl

acem

ent A

mp.

(μm

, 0-p

k) Synchronous component

Direct component XDE Imbalance mass location

FE

DE

0 3 6 9 12 150

20

40

60

80A

mpl

itude

(μm

)

Dis

plac

emen

t Am

p. (μ

m, 0

-pk)


XDE Imbalance mass location

FE

DE

0 3 6 9 12 150

20

40

60

80

Dis

plac

emen

t Am

p. (μ

m, 0

-pk)


XDE Imbalance mass location

FE

DE

0 3 6 9 12 150

20

40

60

80A

mpl

itude

(μm

)( , )

DirectSynchronous

Small Subsynchronous motions at 15 krpm.

Critical speed at ~ 8.2 krpm

Small U

Dis

plac

emen

t Am

p. (μ

m, 0

-pk)


XDE

0 3 6 9 12 150

20

40

60

80

Am

plitu

de (μ

m)

DirectSynchronous

Dis

plac

emen

t Am

p. (μ

m, 0

-pk)


XDE

0 3 6 9 12 150

20

40

60

80

Am

plitu

de (μ

m)

Dis

plac

emen

t Am

p. (μ

m, 0

-pk)


XDE

0 3 6 9 12 150

20

40

60

80

Dis

plac

emen

t Am

p. (μ

m, 0

-pk)


XDE

0 3 6 9 12 150

20

40

60

80

Am

plitu

de (μ

m)

DirectSynchronous

Medium U

ROTORDYNAMIC TESTS ROTORDYNAMIC TESTS –– Air PressurizationAir Pressurization

-FEED AIR PRESSURE increases 40 kPa [6 psig] to 340 kPa [50 psig]

AIR SUPPLY

Small change in stiffness or

rotor centering – shaft cool


0 100 200 300 400 5000

10

20

kPa 204=

spla

cem

ent A

mpl

itude

Subsynchronous components

Running speed

0 100 200 300 400 5000

10

20

kPa 340=

Dis

Frequency (Hz)

0 100 200 300 400 5000

10

20

kPa 40.8=

(μm

)

(a)

(b)

(c)

Subsynchronous components

Running speed

40.8 kPa

204 kPa

340 kPa

Dis

plac

emen

t Am

plitu

de (μ

m)

0 100 200 300 400 500

Frequency (Hz)

0 100 200 300 400 500

0 100 200 300 400 500

20

10

0

20

10

0

20

10

0

Feed pressure increases

X DRIVE END

Notable reduction in

subsynchronous

amplitudeswhen

increasing air feed

pressure

16 krpmsubsync



0 200 400 600 800 10000

20

40

60

80

100,

Frequency [Hz]

Am

plitu

de [m

icro

ns]

50 krpm

2 krpm

1X

26 krpm

Am

plitu

de (μ

m, 0

-pk)

Severe subsynchronous motions at natural frequency

Speed (-)

No feed pressure

Closure:Closure:Subsynchronous motions (onset and amplitude) are

sensitive to level of rotor imbalance – FORCED NONLINEARITY

Subsynchronous frequencies track shaft speed at approximately 50% and lock at natural frequency. Bifurcations to other WFRs found

Air pressurization reduces amplitude of synchronous motions at critical speed.

Increasing air pressures reduce amplitudes of subsynchronous motions

Foil Bearings survived severe instabilities. Synchronous motions may be predictable!


Closure: Gas Bearings for Oil-Free MTM

Dominant challenge for gas bearing technology: intermittent contact and damaging wear at startup & shut down, and temporary rubs during normal operating conditions

Current research focuses on coatings(materials), rotordynamics (stability) & high temperature (thermal management)

– Low gas viscosity requires minute clearances to generate load capacity.

– Damping & rotor stability are crucial– Inexpensive coatings required to reduce drag and wear

(Low speeds and transient HS rubs) – Bearing design & manufacturing process well known– Thermal management to extend operating envelope to

high temperature applications

Need Low Cost & Long Life Solution!

current developments in gas bearings for microturbomachinery...

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