28th Turbomachinery Research Consortium Meeting

Development of a Test Rig for Metal Mesh Foil Gas Bearing and Measurements of Structural Stiffness and Damping in the

Metal Mesh Foil Bearing

Development of a Test Rig for Metal Mesh Foil Gas Bearing and Measurements of Structural Stiffness and Damping in the

Metal Mesh Foil Bearing

Luis San AndrésTae-Ho Kim

Thomas Abraham ChirathadamAlex Martinez

Project title : Metal Mesh-Top Foil Gas Bearings for Oil-Free Turbomachinery: Test Rig for Prototype Demonstration

TAMU past work on Metal Mesh Dampers

Zarzour and Vance (2000) J. Eng. Gas Turb. & Power, Vol. 122

Advantages of Metal Mesh Dampers over SFDsCapable of operating at low and high temperaturesNo changes in performance if soaked in oil

Al-Khateeb and Vance (2001) GT-2001-0247

Test metal mesh donut and squirrel cage( in parallel)MM damping not affected by modifying squirrel cage stiffness

Choudhry and Vance (2005) Proc. GT2005

Develop design equations, empirically based, to predict structural stiffness and viscous damping coefficient

METAL MESH DAMPERS proven to provide large amounts of damping. Inexpensive. Oil-free

Recent Patents: gas bearings & systems

A metal mesh donut is a cheap replacement to “porous foil”

‘Air foil bearing having a porous foil’Ref. Patent No. WO 2006/043736 A1

Turbocharger with hydrodynamic foil bearingsRef. Patent No. US7108488 B2

Foil JournalBearings

Thrust foilBearing

TRC Project: Tasks 07/08

Construction of Metal Mesh Foil Bearings -Assembly of top foil and metal mesh donut inside a cartridge

•Identification of structural force coefficients-Static load-deflection tests for structural stiffness -Dynamic load tests for stiffness and structural loss factor -Effects of frequency

•Construction of test rig for demonstration of MMFB Performance-Turbocharger (TC) driven system

Metal Mesh Foil Bearing (MMFB)

Molding of top foil (Heat treatment)

Top foil (An initial flat strip and a curved, heat treated foil) Top foil within Metal Mesh Donut

MMFB

Metal Mesh Foil Bearings Metal mesh donut and top foil assembled inside a

bearing cartridge. Hydrodynamic air film will develop between rotating shaft

and top foil.

Metal mesh resilient to temperature variations Damping from material hysteresis

Stiffness and viscous damping coefficients controlled by metal mesh material, size (thickness, L, D), and material compactness (density) ratio.

ApplicationReplace oil ring bearings in oil-free PV turbochargers

Metal Mesh Foil Bearings (+/-) No lubrication (oil-free). NO High

or Low temperature limits. Resilient structure with lots of

material damping. Simple construction ( in

comparison with other foil bearings)

Cost effective

Rotordynamic force coefficients unknown

Near absence of predictive models Damping NOT viscous. Modeling

difficulties

MMFB dimensions and specifications

Dimensions and Specifications ValuesBearing Cartridge outer diameter, DBo(mm) 58.15±0.02

Bearing Cartridge inner diameter, DBi(mm) 42.10±0.02

Bearing Axial length, L (mm) 28.05±0.02

Metal mesh donut outer diameter, DMMo (mm) 42.10±0.02

Metal mesh donut inner diameter, DMMi(mm) 28.30±0.02

Metal mesh density, ρMM (%) 20

Top foil thickness, Ttf (mm) 0.076

Metal wire diameter, DW (mm) 0.30

Young’s modulus of Copper, E (GPa), at 21 ºC 110

Poisson’s ratio of Copper, υ 0.34

Bearing mass (Cartridge + Mesh + Foil), M (kg) 0.3160 ± 0.0001

PICTURE

Bearing cartridge

Top foil

Donut shaped metal mesh

Rotating shaft

Gas film

Ω

Static load test setup

Lathe tool holder moves forward and backward : push and pull forces on MMFB

Lathe chuck holds shaft & bearing during loading/unloading cycles.

Lathe tool holder

Eddy Current sensor Load cell

Test MMFB

Stationary shaft

-150

-100

-50

0

50

100

150

-0.07 -0.02 0.03

Displacement, X (mm)

Stat

ic lo

ad,

F (N

)

Push Load

Pull Load

Static Load vs bearing deflection results 3 Cycles: loading &

unloading

Nonlinear F(X)

Large hysteresis loop : Mechanical energy dissipation

MMFB wire density ~ 20%

Displacement: [-0.06,0.06] mmLoad: [-130, 90 ]N

Start

Push load

Pull load

Hysteresis loop

MMFB wire density ~ 20%

Derived MMFB structural stiffness

During Load reversal : jump in

structural stiffness

Max. Stiffness ~ 4 MN/m

Start

Push load

Pull load

Dynamic load tests Motion amplitude controlled mode

Electrodyamic shaker

MMFB Accelerometer Force transducer

Test shaft FixtureTest shaftEddy Current sensors

MMFB motion amplitude (1X) is dominant.

Waterfall of displacement

0

20

40

60

80

100

120

140

160

180

200

0 100 200 300 400 500 600

Frequency [Hz]

Dis

pla

cem

ent [

um

]

1 XIncreasing frequency

12.7, 25.4 &38.1 μm

Frequency of excitation :

25 – 400 Hz (25 Hz interval)

0

10

20

30

40

50

60

70

80

90

0 100 200 300 400Frequency [Hz]

Dyn

amic

load

[N]

12.7 um25.4um38.1 um

At higher frequencies, less force needed to maintain same motion amplitudes

Amplitude of Dynamic Load vs Excitation Frequency

Dynamic load decreases with

increasing frequency and

decreasing motion

amplitudes

38.1 μm

25.4 μm

12.7 μm

Motion amplitude decreases

Identification Model

( )tM x K x C x F

Equivalent Test System

Meq

Keq

Ceq

Fext

x Lf =244 mm Lf =221 mm L= 248 mm

F(t)

X(t)

1-DOF mechanical system

Harmonic force & displacements

Impedance Function

MaterialLOSS FACTOR

Viscous DissipationOr Hysteresis Energy

( ) i tx t X e ( ) i tF t F e

2( )F

Z K M i CX

2

disE K X

2

disE C X

Parameter Identification (no shaft rotation)

KC

1

ImF

K X

-1

-0.5

0

0.5

1

1.5

2

2.5

3

3.5

4

0 100 200 300 400

Frequency [Hz]

Re

al

pa

rt o

f F/X

[M

N/m

]

12.7 um25.4 um38.1 um

Real part of (F/X) decreases with increasing motion amplitude

Real part of (F/X) vs excitation frequency

Natural frequency of the system

Frequency of excitation :

25 – 400 Hz ( 25 Hz step)

2( )K M

12.7 μm

25.4 μm

38.1 μm

Motion amplitude increases

0

0.5

1

1.5

2

2.5

3

3.5

4

0 100 200 300 400

Frequency [Hz]

Str

uc

tura

l Sti

ffn

es

s [

M N

/m]

12.7 um25.4 um38.1 um

Al-Khateeb & Vance model : reduction of stiffness with force magnitude (amplitude dependent)

MMB structural stiffness vs excitation frequency

At low frequencies (25-100 Hz), Stiffness

decreases fast.

At higher frequencies, Stiffness

levels off

MMFB stiffness is frequency and

motion amplitude dependent

Frequency of excitation :

25 – 400 Hz (25 Hz step)K

12.7 um

25.4 um

38.1 um

Motion amplitude increases

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

0 100 200 300 400Frequency [Hz]

Imag

inar

y p

art

of

F

/X [

MN

/m]

12.7 um25.4 um38.1 um

Im (F/X) decreases with

motion amplitude, little

frequency dependency

Imaginary part of impedance (F/X) vs frequency

Frequency of excitation :

25 – 400 Hz ( at 25 Hz interval)C K

12.7 μm

25.4 μm 38.1 μm

Motion amplitude increases

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 100 200 300 400Frequency [Hz]

Str

uctu

ral L

oss

Fact

or

12.7 um25.4 um38.1 um

Loss factor ~ frequency independent at high freqs.

Loss factor vs excitation frequency

Structural damping or loss factor increases

with frequency ( 25-150 Hz)

But, remains nearly constant for higher

frequencies ( 175-400 Hz)

Frequency of excitation :

25 – 400 Hz ( at 25 Hz step)

12.7 μm

25.4 μm

38.1 μm

Model of Metal Mesh damping material

As force increases, more stick-slip joints between wires are freed, thus resulting in a greater number of spring-damper systems in series.

Stick-slip model (Al-Khateeb & Vance, 2002)

Stick-slip model

arranges wires in series connected by dampers and

springs.

Design equation: Metal mesh stiffness/damping

Functions of equivalent modulus of elasticity (Eequiv), hysteresis coeff. (Hequiv), axial length (L), inner radius (Ri), outer radius (Ro), axial compression ratio (CA), radial interference (Rp), motion amplitude (A), and excitation frequency (ω)

, ,equiv o i A pK E f L R R f C f R f A f

, ,equiv o i A pC H g L R R g C g R g A g

2/325 21 4 10 1 2.96 10 1pA

equiv k ko i o i o i

RCL AK E

R R L R R R R

3/ 2 2/325 21 8.7 10 1 1.8 10 1

cpA

equiv co i o i o i n

RCL AC H

R R L R R R R

Empirical design equation for stiffness and equivalent viscous damping coefficients (Al-Khateeb & Vance, 2002)

Stiffness: prediction & test data

Amplitude increases

12.7 μm

25.4 μm

38.1 μm

Markers: Test data

Lines: Prediction

MMFB structural stiffness

decreases as frequency

increases andas motion amplitude increases

Predictions compared to test data: Damping

Amplitude increases

12.7 μm

25.4 μm38.1 μmMarkers: Test data

Lines: Prediction

MMFB equiv. viscous damping

decreases as the excitation

frequency increases and

as motion amplitude increases

Predicted equivalent viscous damping coefficients in good agreement with measurements

Metal Mesh Foil Bearing Rotordynamic Test Rig

(a) Static shaft

Max. operating speed: 120 krpmTurbocharger driven rotorRegulated air supply:9.30bar (120 psig)

Test Journal: length 55 mm, 28 mm diameter , Weight=0.22 kg

Journal press fitted on Shaft Stub

TC cross-sectional viewRef. Honeywell drawing # 448655

Twin ball bearing turbocharger, Model T25, donated by Honeywell Turbo Technologies

Positioning table

Torque arm

Squirrel cage

(b) Front view(a) Right side view

Weight

Static load

TC driving system

Load cellEddy current sensor

Spring

Rotatingjournal

Static load applies upwards : using weights & pulleysArm and load cell to measure bearing torque measurement

Metal Mesh Foil Bearing Rotordynamic Test Rig

Positioning table: Max load 110N Max 3”X 3” travel in two directions Resolution of 1μm

- Supports squirrel cage- Provides motion in two

horizontal directions

Squirrel Cage: - Provides soft support to

MMFB- Maintains concentricity

(prevents tilting) of MMFB with test journal

Metal Mesh Foil Bearing Rotordynamic Test Rig

COST of positioning TABLE: $3631

Conclusions TC driven MMFB rotordynamic test rig under construction

Static and dynamic load tests on metal mesh bearings show large energy dissipation and (predictable) structural stiffness

MMFB stiffness decreases with amplitude of dynamic motion

Large MMFB structural loss factor ( ) at high frequencies

Predicted stiffness and equivalent viscous damping coefficients are in agreement with test coefficients: Test data validates design equations

TRC Proposal: Metal Mesh Foil Bearings for Oil-Free

Turbo-machinery : Rotordynamic performance

Complete construction of turbocharger driven MMFB test rig : squirrel cage, static loading device and torque measurement device

Conduct experiments on test rig Rotor lift off and touch down speeds, measurements of torque & load capacity, vibration and stability (if any)

Identification of dynamic force response Impact loads on test bearing + more measurements of

structural stiffness and loss factor

TA

SK

S

BUDGET FROM TRC FOR 2008/2009: Support for graduate student (20 h/week) x $ 1,600 x 12 months $ 22,008 + Fringe benefits (2.5%) and medical insurance ($ 164/month) Tuition three semesters ($ 3996x3) + Supplies for test rig($ 6004) $ 17,992 Total Cost: $ 40,000