gt2009-59199 flexure pivot hybrid gas bearings keun ryu research assistant asme turbo expo 2009,...

GT2009-59199 Flexure Pivot Hybrid Gas Bearings

Keun RyuKeun RyuResearch Assistant

ASME TURBO EXPO 2009, Orlando, Fla

Dr. Luis San AndrésDr. Luis San AndrésMast-Childs Professor

Fellow ASME

TURBOMACHINERY LABORATORYTEXAS A&M UNIVERSITY

Supported by TAMU Turbomachinery Research Consortium

ASME paper GT2009-59199

Dynamic Forced Response of a Rotor-Hybrid Gas Bearing System

due to Intermittent Shocks


Micro 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


Ideal 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


Thrust of research 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


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

Test rig


Test rig

Positioning Bolt

X

Y

Load

LOP

Rotor/motor

Bearing

Sensors

Load cell

Air supply

Thrust pin


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

Promote stability: no cross-coupled stiffnesses Eliminate pivot wear, contact stresses, pad flutter Minimize manufacturing and assembly tolerances’ stack-up

Flexure pivot tilting pad hybrid bearing

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

worn pads surfaces


Zhu & San Andres (2004) GT 2004-53621 Gas bearing for oil-free applications. Good comparisons with:

TAMU work on flexure pivot tilting bearings

Delgado & San Andres (2004)Computational model for hydrodynamic operation, with application to hybrid brush seals

San Andres (2006)Computational model for hybrid operation validated by Zhu (2004) measurements. Code used by 20+ companies

Stable to 99 krpm

60 KRPM

GT 2004-53614

GT 2004-53621

Journal of Tribology, 129

San Andres & Ryu (2007)Operation with worn clearances and LOP/LBP configuration

J. Eng. Gas Turbines and Power, 2008, 130


2008: 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

J. Eng. Gas Turbines and Power, 2008, v. 130


Objectives:

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.


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)

GT2009-59199 Flexure Pivot Hybrid Gas BearingsRotor 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:


Dominant challenges in gas bearing technology

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

– Bearing design & manufacturing process better known. Load capacity needs minute clearances since gas viscosity is low.

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

low speeds and transient rubs at high speeds

– Engineered thermal management to extend operating envelope to high temperatures

Need Low Cost & Long Life Solution!

GT2009-59199 Flexure Pivot Hybrid Gas Bearings2009 Gas bearing test rig layout

Oscilloscope

Functiongenerator

Power amplifier

Test rig

Electromagnetic shakerTest table

Alignment bolts Rubber O-ringsEddy current

sensors

Trust pin

Imbalance plane

Infrared tachometer

Load cells

Test bearings Motor

Accelerometer

Support springs

Electromagnetic shaker

Test rig base

Air supply

Rotor

cm

connecting rod pushes base plate!

Rubber pad

Hingedfixture

Rotor

Bearing

y

x

Rotationdirection

10°

Coilspring (9 kN/m)

28 cm

GT2009-59199 Flexure Pivot Hybrid Gas BearingsRotor speed coast down tests

2X

1X

Natural freq-193Hz

24Hz (2X12Hz-Excitation freq)

35krpm

2krpm

Frequency [Hz]

0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400

Am

pli

tud

e [m

m]

0.05

0.045

0.04

0.035

0.03

0.025

0.02

0.015

0.01

0.005

0

0

5

10

15

20

0 100 200 300 400 500 600

Frequency [Hz]

Am

pli

tud

e [μ

m]

Amplitude_LV

Synchronous response

Natural frequency

212 Hz

Left bearing

Rotor

Right bearing

LH RH

LV RV

0

0.05

0.1

0.15

0.2

0.25

0.3

0 20 40 60 80 100

Frequency [Hz]

Acc

eler

atio

n [

g]

Acceleration

12 Hz 24 Hz 36 Hz

51 HzExcited frequencies

Excitation frequency: 12 Hz

48 Hz

Ps = 2.36 bar (ab)

Subsynchronous response:1) 24 Hz (Harmonic of 12 Hz)2) Natural frequency 193 Hz

Shaker input frequency: 12Hz

Synchronous Dominant! excitation of system natural frequency

is NOT an instability!

gt2009-59199 flexure pivot hybrid gas bearings keun ryu research assistant asme turbo expo 2009,...

Documents

gas foil

pivot wear

shock operation slide

hybrid brush seals san

available slide

extreme bearing loads

dc motor test rig slide

simple low cost