Gas Bearings for Oil-Free Turbomachinery 28th Turbomachinery Consortium Meeting Dynamic Forced...

Gas Bearings for Oil-Free Turbomachinery28th Turbomachinery Consortium Meeting

Dynamic Forced Response of a Rotor-Hybrid Gas Bearing System

due to Intermittent Shocks

TRC-B&C-1-08

2008 TRC Project

GAS BEARINGS FOR OIL-FREE TURBOMACHINERY

Keun RyuKeun RyuResearch Assistant

Luis San AndrésLuis San AndrésMast-Childs ProfessorPrincipal Investigator

Gas Bearings for Oil-Free TurbomachineryMicro Turbomachinery (< 0.5 MW)

• High energy density • Compact and fewer parts• Portable and easily sized• Lower pollutant emissions• Low operation cost

ADVANTAGES

• Oil-Free bearing • High rotating speed (DN value>4M)• Simple configuration• Lower friction and power losses• Compact size

Gas bearings

AIAA-2004-5720-984

Gas Foil Bearing

GT 2004-53621

Flexure pivot Bearing

ASME Paper No. GT2002-30404

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

Gas Bearings for Oil-Free Turbomachinery

Gas bearings for micro turbomachinery (< 0.5 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 Bearings for MTM


Thrust in TRC program:

Investigate conventional bearings of low cost, easy to manufacture (common materials) and easy to install & align.

Combine hybrid (hydrostatic/hydrodynamic) bearings with low cost coating to allow for rub-free operation at start up and shut down

Major issues: Little damping, Wear at start & stop, Instability (whirl & hammer), & reliability under shock operation

Gas Bearings for MTM


Max. operating speed: 100 kpm3.5 kW (5 Hp) AC integral motor

Rotor: length 190 mm, 28.6 mm diameter, weight=0.826 kg

Components of high-speed gas bearing test rig

Rig housing

Bearing shell andLoad cells

Gas bearing

Bearing cover

Shaft and DC motor

Gas bearing test rig


2007: Control of bearing stiffness / critical speed

Peak motion at “critical speed” eliminated by controlling supply pressure into bearings

Controller activated system

Displacements at RB(H)

L R

V: verticalH: horizontal

5.08 bar

2.36 barBlue line: Coast down

Red line: Set speed

2.36 bar5.08 bar

Gas Bearings for MTM GT 2008-50393


Demonstrate the rotordynamic performance, reliability, and durability of hybrid gas bearings

•Rotor motion measurements for increasing gas feed pressures and speed range to 60 krpm.

•Install electromagnetic pusher to deliver impact loads into test rig.

•Perform shock loads (e-pusher & lift-drop) tests to assess reliability of gas bearings to withstand intermittent shocks without damage.

2007-2008 Objectives


Clearances Cp =38 & 45 m, Preload =7 & 5 m (~20%)Web rotational stiffness=20 Nm/rad

TEST gas bearings

Air Feeding

holeφ0.62

33.2

Section A-A

16.5Web length

16.6

φ62.48

A

A

120°

28.56

Load Cells

Pressurized air supply

PadFlexure web

Ω

Shaft rotation

1.0

7.0

43.2°72°

LOP

X

YRotor

Casing

worn pads surfaces

Flexure Pivot Hybrid Bearings: Promote stability, eliminate pivot wear, engineered product with many commercial applications

TEST gas Bearings


cmcmElectricmotor

Load cells

Infrared tachometer


Thrust pin

Flexure pivot pad bearing

Eddy current sensors

Alignment Bolts

Imbalance plane

RB: Right bearingLB: Left bearing

LB RB

Base plate

Hitting rod

Test table

Electromagnetic pusher

Load cellRubber pad

Accelerometer

Accelerometer

Plunger

Solenoid

Lifting handle

Rotor

Plastic pad

Supporting stand

E-pusher: Push type solenoid

240 N at 1 inch stroke

2008 Gas Bearing test rig layout


Load cell



Alignment Bolt

Base plate

Hitting rod

Test table

Load cell

Rubber pad

Accelerometer (A1)

Accelerometer (A2)

Plunger

Solenoid

RotorGas bearing

Hinged fixture

cmcm Plastic pad

-5

0

5

10

15

20

25

0 0.1 0.2 0.3 0.4 0.5

Time [s]

Acc

ele

rati

on

[g

]

Impact from e-pusher

Shock after dropping

0

0.4

0.8

1.2

1.6

0 200 400 600 800

Frequency [Hz]

Ac

ce

lera

tio

n [

g]

Electromagnetic pusher tests

Impact duration ~20 msE-force ~400 N (pk-pk)

Multiple impact


Load cell



Alignment Bolt

Base plate

Test table

Rubber pad

Accelerometer (A1)

Accelerometer (A2)

Manual lifting

RotorGas bearing

Lifting handle

Hinged fixture

cmcm

-5

0

5

10

15

20

25

0 0.1 0.2 0.3 0.4 0.5

Time [s]

Acc

ele

rati

on

[g

]

Shock from dropping

Shock from bounce

0

0.4

0.8

1.2

1.6

0 200 400 600 800

Freqeuncy [Hz]

Ac

ce

lera

tio

n [

g]

Manual lift & drop tests

Multiple impact

Lift off to 5~15 cm (10~30° rotation)


-30

-25

-20

-15

-10

-5

0

5

10

15

20

0 0.05 0.1 0.15 0.2

Time [s]

Acc

ele

rati

on

[g

]

Ro

tor

res

po

ns

e [m

m]

0

-0.05

0.05

0.1

0.15

0.2Test rig base plate

Left bearing housing

Rotor response at LH

Shock from dropping

Impact from e-pusher0

100

200

300

400

500

600

0 20 40 60 80 100 120

Coast down time [sec]

Fo

rce

[N

, p

k-p

k]

Impact force from e-pusher

Rotor speed

Rotor speed [krpm]

Measured impact force

Ro

tor

sp

ee

d [

krp

m]

60

50

40

20

30

10

0

Shock ~15 gTransient rotor response ~ 40 µm

46 krpm

Intermittent shocksImpact force 100~400 N

Displacements at LB(H)

L R


Ps=5.08 bar (ab)

Coast down: E-pusher tests


0

5

10

15

20

0 10000 20000 30000 40000 50000 60000

Rotor speed [rpm]

Acc

eler

atio

n [

g,

pk-

pk]

Acceleration on test rig base plate

Shock induced acceleration

At base 5~20 gAt housing 5~10 g

Beyond critical speed: Synchronous frequency is isolated from shocks

Below 20 krpm:Large fluctuation of synchronous response

Ps=3.72 bar (ab)

Displacements at LB(H)

L R


Coast down: manual lift & drop tests

Chart Title

0

5

10

15

20

25

0 10000 20000 30000 40000 50000 60000

Rotor peed [rpm]

Am

plit

ud

e [μ

m, p

k-p

k]

No shock

Lift-drop test

Coast down time (lift-drop test)

No shock

Lift-drop test

Coast down time (lift-drop test) 60

40

20

0

Co

adt

do

wn

tim

e [s

ec]

80

100

Rotor synchronous response


0.04

0.03

2 krpm

0.02

0.01

1X 2X

0 60 krpm0 250 500 750 1000 1250 1500 1750 2000

Frequency [Hz]

Rotor speed

decreases

Excitation of rotor natural frequency. NOT a rotordynamic instability!

Ps=2.36 bar (ab)Displacements

at LB(H)

L R


Waterfall: manual lift & drop tests


Overall rotor amplitude increases largely. Subsynchronous amplitudes larger than synchronous

0

5

10

15

0 10 20 30 40 50 60

Rotor speed [krpm]A

mp

litu

de

[μm

, R

MS

]

Synchronous

Subsychronous

Subsynchronous

Synchronous(slow roll

compensated)

Rotor response: manual lift & drop tests

Ps=2.36 bar (ab)

Shock loads applied Shock loads applied

Chart Title

50

65

80

95

110

125

140

0 10000 20000 30000 40000 50000 60000

Rotor speed [rpm]

Am

plitu

de [μ

m, p

k-pk

]

No shock

Lift-drop test

5.08 bar (ab) feed pressure into bearings

No shock

Lift-drop test

Rotor overall response

No slow roll compensation


0

5

10

15

0 50 100 150 200 250 300

Whirl frequency [Hz]

Wh

irl

amp

litu

de

[μm

, R

MS

]0

50

100

150

200

250

300

0 10 20 30 40 50 60

Rotor speed [krpm]

Wh

irl

freq

uen

cy [

Hz]

Natural frequency of rotor-bearing system (150~190 Hz)

Natural frequency of test rig (~40 Hz)

Rotor-bearing natural frequency increases with rotor

speed. Natural frequency of test rig also excited.

Rotor response: manual lift & drop tests

Ps=2.36 bar (ab)

Gas Bearings for Oil-Free TurbomachineryRotor response: manual lift & drop tests

15 krpmDrop induced shocks ~30 g

Transient responseFull recovery within

~ 0.1 sec.

Ps=2.36 bar (ab)

-40

-30

-20

-10

0

10

20

30

0 0.05 0.1 0.15 0.2

Time [s]

Ac

ce

lera

tio

n [

g]

Ro

tor

res

po

ns

e [

mm

]

Test rig base plate

Left bearing housing

Rotor response at LH

Shock from bounce

Shock from dropping

0.2

0

0.05

0.1

-0.05

0.15

0.2

0.25

0.3


With feed pressure: long time to coast down demonstrates very low viscous drag!

0

10

20

30

40

50

60

70

0 20 40 60 80 100 120


Ro

tor

sp

ee

d [

krp

m]

5.08 bar, No shock

3.72 bar, No shock

2.36 bar, No shock

5.08 bar

2.36 bar

3.72 bar

Dry friction

(contact)

Rotor speed vs time (No shocks)


0

10

20

30

40

50

60

0 10 20 30 40 50 60 70 80 90


Ro

tor

sp

ee

d [

krp

m]

Rotor speed

Shock to test rig

Measured shock on test rig base plate

Acc

eler

atio

n [

g,

pk-

pk]Rotor speed [krpm]

60

50

40

20

30

10

0


Drop-down test

Exponetial decay,

R2=98.99%

Linear decay,R2=99.03%

0

10

20

30

40

50

60

0 10 20 30 40 50 60 70 80 90


Ro

tor

sp

eed

[k

rpm

]

Rotor speed

Shock to test rig


Measured shock on test rig base plate

Acc

ele

rati

on

[g

, pk

-pk

]

Rotor speed [krpm]

60

50

40

20

30

10

0

Drop-down test

Exponetial decay,

R2=98.45%Linear decay,

R2=98.33%

Overall coast down time reduces with

shock loads (~ 20 sec)

Exponential decay (No rubs) even under severe external shocks

Rotor speed vs time (Manual lift-drop tests)

No shocks

No shocks


• Under shock loads ( up to ~30 g), natural frequency of rotor-bearing system (150-200 Hz) and test rig base (~ 40 Hz) excited. However, rotor transient motions quickly die!

• For all feed pressures (2-5 bar), rotor transient responses from shocks restore to their before impact amplitude within 0.1 second. Peak instant amplitudes (do not exceed ~50 µm)

• Even under shock impacts, viscous drag effects are dominant, i.e., no contact between the rotor and bearing.

• Hybrid bearings demonstrate reliable dynamic performance even with WORN PAD SURFACES

Conclusions


TRC Proposal: Gas Bearings for Oil-Free Turbo-

machinery – Identification of Bearing Force Coefficients from Base-Induced Excitations

• Set up an electromagnetic shaker to deliver excitations (periodic loads of varying frequency) to the test rig.

• Measure the rotor response due to base induced excitations.

• Identify frequency dependent bearing stiffness and damping coefficients from measured rotor transient responses at increasing rotor speeds.

• Compare the identified bearing force coefficients to predictions from XLTRC2 computational models.

TA

SK

S

BUDGET FROM TRC FOR 2008/2009: Support for graduate student (20h/week) x $ 1,600 x 12 months,

Fringe benefits (2.5%) and medical insurance ($194/month) $ 22,008 Tuition & fees three semesters ($3,996x3) + Supplies for test rig $ 17,992 Total Cost: $ 40,000


Electromagnetic shakerShaker force peak amplitude (sine): 98 N (22 lbf)Useful frequency range: 5 ~ 9000 Hz

Identify frequency dependent bearing force coefficients at increasing rotor speeds

Operating rotor speed range: 170 Hz ~ 1 kHz 10 krpm ~ 60 krpm

Z

X

Y

LDS V406/8 – PA 100E

Low frequency excitations: simulate roadsurface effect on MTM

Gas Bearings for Oil-Free Turbomachinery 28th Turbomachinery Consortium Meeting Dynamic Forced...

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