Grooved Oil Seals: Force Coefficients GT2011-45274 1 A Novel Bulk-Flow Model for Improved...

1

Grooved Oil Seals: Force CoefficientsGT2011-45274

A Novel Bulk-Flow Model for Improved Predictions of Force Coefficients in

Grooved Oil Seals Operating Eccentrically

accepted for journal publication

ASME GT2011-45274

Luis San AndrésMast-Childs Professor

Texas A&M University

Adolfo Delgado Mechanical Engineer

GE Global Research Center

Supported by TAMU Turbomachinery Research Consortium

Presentation available at http://rotorlab.tamu.edu

ASME Turbo Expo 2011 Power for Land, Sea and Air June 6-10, 2011, Vancouver, BC

2


Shaft

Outer seal

Inner seal

Oil supply (PS+P)

Process Gas (PS) Pa

Outer seal land

Inner seal land

Anti-rotation pin Seal loading spring

Oil Seals

Oil seal in a compressor [1]

- Locked oil seal rings can induce instability in compressors.

- A common remedy: seals are grooved to reduce cross-coupled stiffness and lower lock-up forces

commonly used to prevent leakage of process fluid in centrifugal compressors.

Kirk, R., 1986, “Oil Seal Dynamic Considerations for Analysis of Centrifugal Compressors,” Proc. 15th Turbomachinery Symposium,

Houston, TX, pp. 25-34.

3


- Grooves should reduce force coefficients by a factor of four, i.e.

Semanate and San Andrés, (1993)

KXY (1 land)= 4 KXY(2 lands)

CXX (1 land)= 4 CXX(2 lands)

-Fluid inertia effects not predicted (assumed negligible)

Predictive Models

Baheti and Kirk, (1995)

- Reynolds and energy equation (FEM)- Grooves should effectively isolate seal lands - Cross-coupled stiffness and damping coefficients are reduced by ~60 % for grooved configurations

- Bulk flow equation model

4


2L

c

Journal

Constant pressure

Short length seal

Damping, Cross-coupled Stiffness & Inertia

3 3

3

18 ; ; 8

4 2 20XX XY XX XX

D L D LC K C M

c c

2-land seal: (deep groove divides lands)

3 3

3

1; ;

4 2 20XX XY XX XX

D L D LC K C M

c c

L

c

30c

5c

3 3

3

12 ; ; 2

4 2 20XX XY XX XX

D L D LC K C M

c c

Coeffs are ¼ of original seal

5


[1] Graviss, M., 2005, “The Influence of a Central Groove on Static and Dynamic Characteristics of an Annular Liquid Seal with Laminar Flow,” M.S. Thesis, Texas A&M Univ., College Station, TX.

Parallel oil seal configuration [1]

17 mm

76c

c

25 mm

136c

Oil supplySeal length

Journal

Parallel seal configuration (balance thrust force due to pressure drop across the seals)

Includes ‘deep’ inlet (central) groove to feed seals

Parameter identification: FSEAL= 1/2 FTest conf.

Predictions do not consider groove or fluid inertia effects (Zirkelback and San Andrés 1996)

Smooth& grooved oil seals: Smooth& grooved oil seals: test resultstest results

Childs et al., (2006, 2007)

Results Force coefficients are well predicted (C,K) except added mass coefficients

Large added mass coefficients (~15 kg)

Added mass predictions using Classical model (Reinhardt & Lund – 1975) (single land- i.e. not including inlet groove) (2.84 kg)

6


Old Predictions Experiments≠

Inner land groove should reduce crossed-coupled stiffness and direct damping coefficients by a factor of four

Groove does not effectively separate seal lands

Kxy (1 land)= 4 Kxy(2 lands)

Cxx (1 land)= 4 Cxx(2 lands)

≠Null (neglected) added mass coefficients

Large added mass coefficients, increasing with increasing groove depth

Need for better predictive models

Inlet (central) groove not considered (null dynamic pressure). Ignores fluid inertia

Large added mass coefficients

≠At most:

KXY (1 land)= 2 KXY(2 lands)

CXX (1 land)= 2 CXX(2 lands)

7


Ps- Pd >0

Pd :discharge pressure

yz

feed plenum groove

mid-land groove

oil supply, Ps

Streamlines in axially symmetric grooved annular cavity.

Pd

Pd

Fluid flow predictive modelFluid flow predictive model • Bulk flow for incompressible liquid

• Qualitative observations of laminar flow field

• Boundary Conditions

• Characteristic groove depth

Delgado, A., and San Andrés, L., 2010, “A Model for Improved Prediction of Force Coefficients in Grooved Squeeze Film Dampers and Oil Seal Rings,” ASME J. Tribol., 132

8


, ,...I II N

Linear fluid inertia modelLinear fluid inertia model

3 3 12 6P P

h h h R hx x z z t x

n+1

Oil supply

zI zIIIzIIzIV

1 2 3 4

zN

nIV NIIIIII

No fluid inertia advection

In each flow region:

2

22

h ht

with temporal fluid inertiaReynolds equation

9

Grooved Oil Seals: Force CoefficientsGT2011-45274Finite Element Solution Off-centered operation

x=R

Y

X

e

h

R e

0 cos sini tX Yh = h + e ( ) + e ( )e

Film thickness

10


n+1

Oil supply

zI zIIIzIIzIV

1 2 3 4

zN

n

IV NIIIIII

Boundary conditionsBoundary conditions

No generation of dynamic pressure

First-order pressures and axial flow rates must be equal

Null axial flow rate(axial symmetry)

PaPa

Ps= supply pressurePa= ambient pressure

Laminar flow

Ps

11


e

x=R

z Nodal pressures

q Flow rate

Flowdomain

0 01

pe

i

ne e

ii

P P

k P q fije e

j

n

ie

ie

j

pe

01

3

, , , , 12e

eee

ij i x j x i z j z

hk dx dz

. 2i

e

e ei x

Rf h dx dz

Assemble system of

equations, impose

boundary conditions and solve

3 2 2

212 2 12

h h h h hP

t t

Finite Element for solution of Reynolds Eqn.Finite Element for solution of Reynolds Eqn.

12


Consider small amplitude journal (rotor) motions about a static equilibrium position (SEP)

Small amplitude journal motions about an equilibrium position

An applied external static load (Wo)

determines the rotor equilibrium position (eX,

eY)o with steady pressure field Po and film

thickness ho

Let the journal whirl with frequency and

small amplitude motions (eX, eY) about the equilibrium position. Hence

,tiXXoX eeee

,tiYYoY eeee

Wo X

Y

eXo

eY

eo

X

clearancecircle

Y

Static load

Journal center

Wo X

Y

eXo

eY

eo

X

clearancecircle

Y

Static load

Journal center

Perturbation analysis of flow equations

13

Grooved Oil Seals: Force CoefficientsGT2011-45274Seal dynamic reaction forces

Stiffness coefficients

Damping coefficients

Force coefficients are independent of excitation frequency for incompressible fluid. Force coefficients depend on rotor speed & static load

XY

Z

Lateral displacements (X,Y)

X XX XY XX XY XX XY

Y YX YY YX YY YX YYB B B

F K K C C M MX X X

F K K C C M MY Y Y

Inertia coefficients

Measure of stability: Whirl frequency ratio

WFR = Kxy/(Cxx

14


z

x=R

Inlet

Test Grooved Oil Seal & FE mesh Childs, D. W., Graviss, M., and Rodriguez, L. E., 2007, “The Influence of Groove Size on the Static & Rotordynamic Characteristics of Short, Laminar-Flow Annular Seals,” ASME J. Tribol, 129(2), 398-406.

Clearance = 86 m

Journal diameter: 117 mm

Parallel oil seals Configuration [Childs et al]

17 mm

76c

c(0-15) c

25 mm

136c

Oil supplySeal length

Discharge plenum

Buffer sealJournal

2 mm

12

34

e

e

0h

Outlet plane

z

Inlet plane0 2

Grooves

x=R

15

Grooved Oil Seals: Force CoefficientsGT2011-45274Boundary conditions

P(,z)=P(+2,z)

Outlet plane

x

z

Groove

Groove

P=Psupply

Inlet plane

P=Pexit

Zeroth Order Pressure Field

Constant static pressure at inlet plane

Constant static pressure at exit plane

First Order Pressure Field

Zeroth and first order pressure and flow fields are periodic in circumferential direction

Null dynamic pressure at exit plane

Null axial flow rate (axial symmetry)

If oil cavitation (Pcav=0), the first

order dynamic pressure field

vanishes

Flow continuity is automatically satisfied

at boundaries

Laminar flow

16

Grooved Oil Seals: Force CoefficientsGT2011-45274Groove effective depthGroove effective depth

Test seal

CFD simulations show streamline separating flow regions IS a physical boundary delimiting the domain for squeeze film flow due to journal radial motions.

Inner land groove close up (CFD -Pressure driven flow)

Laminar flow

Ps= supply pressurePa= ambient pressure

10c

15c

Pa

Ps

17


z

x=R

Inlet

Test Grooved Oil SealChilds, D. W., Graviss, M., and Rodriguez, L. E., 2007, “The Influence of Groove Size on the Static & Rotordynamic Characteristics of Short, Laminar-Flow Annular Seals,” ASME J. Tribol, 129(2), 398-406.

x=R

Diameter 117 mm

Land length 24.89 mm

Radial land clearance, c 85.9 mm

Central groove length 17 mm

Central groove depth 136c

Inner land groove length 2 mm

Inner land groove depth 0c and 15c

Static journal eccentricity (e/c) 0-0.7

Shaft speed 4,000-10,000 rpm

Supply pressure 70 bar

Oil density 850 kg/m3

Oil viscosity (smooth seal) 0.016 Pa.s (54 0C)

Oil viscosity (grooved seal) 0.019 Pa.s (49 0C)

Effective depths in model

Central groove = 9c

Inner land groove = 6c

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Grooved Oil Seals: Force CoefficientsGT2011-45274Test oil seal operating conditions

-1.0

-0.8

-0.5

-0.3

0.0

0.3

0.5

0.8

1.0

-1.0 -0.8 -0.5 -0.3 0.0 0.3 0.5 0.8 1.0

ex

e y

smooth seal

Grooved seal

Load

Smooth seal

Grooved seal

Journal center locus shows oil seal

operates with oil cavitation at the

largest test eccentricities (large

static load)Journal locus

Shaft speed: 10,000 rpm

Static eccentricity ratio: 0, 0.3, 0.5, 0.7

Supply pressure: 70 bar

Test data

Childs, D. W., Graviss, M., and Rodriguez, L. E., 2007, “The Influence of Groove Size on the Static & Rotordynamic Characteristics of Short, Laminar-Flow Annular Seals,” ASME J. Tribol, 129(2), 398-406.

19


0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0 0.1 0.2 0.3 0.4 0.5 0.6

Static journal eccentricity ratio (e/c)

Lea

kag

e [k

g/s

]

Oil Seal Leakage

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0 0.1 0.2 0.3 0.4 0.5 0.6

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0 0.1 0.2 0.3 0.4 0.5 0.6


Lea

kag

e [k

g/s

]

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0 0.1 0.2 0.3 0.4 0.5 0.6


Lea

kag

e [k

g/s

]

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0 0.1 0.2 0.3 0.4 0.5 0.6

0

5001000

1500

2000

25003000

3500

4000

0 1

Smooth seal- Predictions

Smooth seal- Experiments

Grooved seal- Predictions

Grooved seal- Experiments

Predicted leakage

correlates very well with tests

for both smooth land and grooved

seal

Smooth Seal

Grooved Seal

(cg= 15c)

(c = 7c)

10,000 rpm, 70 bar

Figure 14

20


0

1000

2000

3000

4000

5000

6000

7000

8000

0 0.2 0.4 0.6 0.8


Fo

rce [

N]

0

1000

2000

3000

4000

5000

6000

7000

8000

0 0.2 0.4 0.6 0.8

Journal eccentricity ratio (e/c)

Forc

e [N

]

Smooth seal- Theory


Grooved seal-Theory


0

1000

2000

3000

4000

5000

6000

7000

8000

0 0.2 0.4 0.6 0.8


Forc

e [N]

Smooth seal- Theory


Grooved seal-Theory


0

1000

2000

3000

4000

5000

6000

7000

8000

0 0.5 1


Fo

rce [

N]

Smooth seal- Theory


Grooved seal-Theory


0

1000

2000

3000

4000

5000

6000

7000

8000

0 0.5 1


Fo

rce [

N]

Smooth seal- Theory


Grooved seal-Theory


0

1000

2000

3000

4000

5000

6000

7000

8000

0 0.5 1


Fo

rce [

N]





0

5001000

1500

2000

25003000

3500

4000

0 1





Oil Seal Forces

At high eccentricity, test data shows larger seal reaction force for smooth & grooved seals

Smooth Seal

Grooved Seal

KXX

10,000 rpm, 70 bar

(cg= 15c)

(c = 7c)

Figure 7

21


0

50

100

150

200

250

0 0.1 0.2 0.3 0.4 0.5 0.6


Sti

ffn

es

s [

MN

/m]

0

1000

2000

3000

4000

5000

6000

7000

8000

0 0.2 0.4 0.6 0.8

Journa l ecce ntricity ra tio (e /c)

Fo

rce

[N

]

Smooth seal- Theory


Grooved seal-Theory


0

1000

2000

3000

4000

5000

6000

7000

8000

0 0.2 0.4 0.6 0.8

Journal eccentricity ratio (e /c)

Forc

e [N

]

Smooth seal- Theory


Grooved seal-Theory


0

1000

2000

3000

4000

5000

6000

7000

8000

0 0.5 1


Fo

rce [

N]

Smooth seal- Theory


Grooved seal-Theory


0

1000

2000

3000

4000

5000

6000

7000

8000

0 0.5 1


Fo

rce [

N]

Smooth seal- Theory


Grooved seal-Theory


0

1000

2000

3000

4000

5000

6000

7000

8000

0 0.5 1


Fo

rce [

N]





KYY

-50

0

50

100

150

200

250

0 0.1 0.2 0.3 0.4 0.5 0.6


Sti

ffn

es

s [

MN

/m]

KXX

0

1000

2000

3000

4000

5000

6000

7000

8000

0 0.2 0.4 0.6 0.8

Journa l ecce ntricity ra tio (e /c)

Fo

rce

[N]

Smooth seal- Theory


Grooved seal-Theory


0

1000

2000

3000

4000

5000

6000

7000

8000

0 0.2 0.4 0.6 0.8

Journal eccentricity ratio (e /c)

Forc

e [N

]

Smooth seal- Theory


Grooved seal-Theory


0

1000

2000

3000

4000

5000

6000

7000

8000

0 0.5 1


Fo

rce [

N]

Smooth seal- Theory


Grooved seal-Theory


0

1000

2000

3000

4000

5000

6000

7000

8000

0 0.5 1


Fo

rce [

N]

Smooth seal- Theory


Grooved seal-Theory


0

1000

2000

3000

4000

5000

6000

7000

8000

0 0.5 1


Fo

rce [

N]





0

5001000

1500

2000

25003000

3500

4000

0 1





Oil Seal Direct Stiffness

Model predicts well direct stiffness for smooth & grooved

sealsSmooth Seal

Grooved Seal

Smooth Seal

Grooved Seal

KYY

KXX

10,000 rpm, 70 bar

(cg= 15c)

(c = 7c)

Figure 8

22


-200

-150

-100

-50

0

50

100

150

0 0.1 0.2 0.3 0.4 0.5 0.6


Stif

fn

es

s [

MN

/m]

-200

-150

-100

-50

0

50

100

0 0.1 0.2 0.3 0.4 0.5 0.6


Stif

fn

es

s [

MN

/m]

KXY

KYX

0

1 0 0 0

2 0 0 0

3 0 0 0

4 0 0 0

5 0 0 0

6 0 0 0

7 0 0 0

8 0 0 0

0 0 . 2 0 . 4 0 . 6 0 . 8

J o u r n a l e c c e n tr i c i ty r a t i o (e / c )

Fo

rc

e [

N] Smooth seal- Theory


Grooved seal-Theory


0

1000

2000

3000

4000

5000

6000

7000

8000

0 0.2 0.4 0.6 0.8

Journa l e cce ntricity ra tio (e /c)

Fo

rc

e [N

]

Smooth seal- Theory


Grooved seal-Theory


0

1000

2000

3000

4000

5000

6000

7000

8000

0 0.5 1


Fo

rce [N

]

Smooth seal- Theory


Grooved seal-Theory


0

1000

2000

3000

4000

5000

6000

7000

8000

0 0.5 1


Force [N

]

Smooth seal- Theory


Grooved seal-Theory


0

1000

2000

3000

4000

5000

6000

7000

8000

0 0.5 1


Fo

rc

e [N

]





0

1 0 0 0

2 0 0 0

3 0 0 0

4 0 0 0

5 0 0 0

6 0 0 0

7 0 0 0

8 0 0 0

0 0 . 2 0 . 4 0 . 6 0 . 8


Fo

rc

e [



Grooved seal-Theory


0

1000

2000

3000

4000

5000

6000

7000

8000

0 0.2 0.4 0.6 0.8


Fo

rc

e [N

]

Smooth seal- Theory


Grooved seal-Theory


0

1000

2000

3000

4000

5000

6000

7000

8000

0 0.5 1


Fo

rce [N

]

Smooth seal- Theory


Grooved seal-Theory


0

1000

2000

3000

4000

5000

6000

7000

8000

0 0.5 1


Force [N

]

Smooth seal- Theory


Grooved seal-Theory


0

1000

2000

3000

4000

5000

6000

7000

8000

0 0.5 1


Fo

rc

e [N

]





-200

-150

-100

-50

0

50

100

150

0 0.1 0.2 0.3 0.4 0.5 0.6


Stif

fn

es

s [

MN

/m]

-200

-150

-100

-50

0

50

100

0 0.1 0.2 0.3 0.4 0.5 0.6


Stif

fn

es

s [

MN

/m]

KXY

KYX

0

1 0 0 0

2 0 0 0

3 0 0 0

4 0 0 0

5 0 0 0

6 0 0 0

7 0 0 0

8 0 0 0

0 0 . 2 0 . 4 0 . 6 0 . 8


Fo

rc

e [



Grooved seal-Theory


0

1000

2000

3000

4000

5000

6000

7000

8000

0 0.2 0.4 0.6 0.8


Fo

rc

e [N

]

Smooth seal- Theory


Grooved seal-Theory


0

1000

2000

3000

4000

5000

6000

7000

8000

0 0.5 1


Fo

rce [N

]

Smooth seal- Theory


Grooved seal-Theory


0

1000

2000

3000

4000

5000

6000

7000

8000

0 0.5 1Journal eccentricity ratio (e/c)

Force [N]

Smooth seal- Theory


Grooved seal-Theory


0

1000

2000

3000

4000

5000

6000

7000

8000

0 0.5 1


Fo

rce [N

]





0

1 0 0 0

2 0 0 0

3 0 0 0

4 0 0 0

5 0 0 0

6 0 0 0

7 0 0 0

8 0 0 0

0 0 . 2 0 . 4 0 . 6 0 . 8


Fo

rc

e [



Grooved seal-Theory


0

1000

2000

3000

4000

5000

6000

7000

8000

0 0.2 0.4 0.6 0.8


Fo

rc

e [N

]

Smooth seal- Theory


Grooved seal-Theory


0

1000

2000

3000

4000

5000

6000

7000

8000

0 0.5 1


Fo

rce [N

]

Smooth seal- Theory


Grooved seal-Theory


0

1000

2000

3000

4000

5000

6000

7000

8000

0 0.5 1Journal eccentricity ratio (e/c)

Force [N]

Smooth seal- Theory


Grooved seal-Theory


0

1000

2000

3000

4000

5000

6000

7000

8000

0 0.5 1


Fo

rce [N

]





0

5001000

1500

2000

25003000

3500

4000

0 1





Oil Seal Cross Stiffness

Model predicts well decrease in cross-

stiffness when adding inner groove

Smooth Seal

Grooved Seal

Smooth Seal

Grooved Seal

KYX

KXY

10,000 rpm, 70 bar

(cg= 15c)

(c = 7c)

Figure 9

23


0

10

20

30

40

50

60

0 2000 4000 6000 8000 10000 12000

Rotor speed (RPM)

Sti

ffn

es

s [

MN

/m]

0

10

20

30

40

50

60

0 2000 4000 6000 8000 10000 12000

Rotor speed (RPM)

Sti

ffn

es

s [

MN

/m]

0

10

20

30

40

50

60

0 2000 4000 6000 8000 10000 12000

0

10

20

30

40

50

60

0 2000 4000 6000 8000 10000 12000

0

5001000

1500

2000

25003000

3500

4000

0 1





0

10

20

30

40

50

60

0 2000 4000 6000 8000 10000 12000

Rotor speed (RPM)

Sti

ffn

ess

[M

N/m

]

0

10

20

30

40

50

60

0 2000 4000 6000 8000 10000 12000

Rotor speed (RPM)

Sti

ffn

ess

[M

N/m

]

0

10

20

30

40

50

60

0 2000 4000 6000 8000 10000 12000

Rotor speed (RPM)

Sti

ffn

es

s [

MN

/m]

0

10

20

30

40

50

60

0 2000 4000 6000 8000 10000 12000

Rotor speed (RPM)

Sti

ffn

es

s [

MN

/m]

0

10

20

30

40

50

60

0 2000 4000 6000 8000 10000 12000

Rotor speed (RPM)

Sti

ffn

es

s [

MN

/m]

0

10

20

30

40

50

60

0 2000 4000 6000 8000 10000 12000

Rotor speed (RPM)

Sti

ffn

es

s [

MN

/m]

Model effectively predicts reduction

in cross-coupled stiffness due to mid-

land groove.

Smooth Seal

Grooved Seal

KXY

KXY

Eccentricity=0.3

Eccentricity=0e= 0.0, 0.3

Smooth Seal

Grooved Seal

(cg= 15c)

(c = 7c)

Oil Seal Cross-Stiffnesses 70 bar

Figure 10

rotor speed increases

24


0

5001000

1500

2000

25003000

3500

4000

0 1





Oil Seal Direct Damping

0

100

200

300

0 0.2 0.4 0.6


Dam

pin

g [

kN.s

/m]

0

100

200

300

0 0.2 0.4 0.6

Static journal eccentricity ratio (e/c )

Da

mp

ing

[k

N.s

/m]

0

100

200

300

0 0.2 0.4 0.6


Dam

pin

g [

kN.s

/m]

0

100

200

300

0 0.2 0.4 0.6

Static journal eccentricity ratio (e/c )

Da

mp

ing

[k

N.s

/m]

0

100

200

300

0 0.2 0.4 0.6


0

100

200

300

0 0.2 0.4 0.6

0

100

200

300

0 0.2 0.4 0.6


0

100

200

300

0 0.2 0.4 0.6

Model predicts accurately reduction

in direct damping due to inner land groove.

Smooth Seal

Grooved Seal

Smooth Seal

Grooved Seal

CYY

CXX

10,000 rpm, 70 bar

(cg= 15c)

(c = 7c)

Figure 11

25


-150

-100

-50

0

50

0 0.2 0.4 0.6


Dam

pin

g [

kN.s

/m]

CYX

0

1000

2000

3000

4000

5000

6000

7000

8000

0 0.2 0.4 0.6 0.8


Fo

rce

[N]

Smooth seal- Theory


Grooved seal-Theory


0

1000

2000

3000

4000

5000

6000

7000

8000

0 0.2 0.4 0.6 0.8


Forc

e [N

]

Smooth seal- Theory


Grooved seal-Theory


0

1000

2000

3000

4000

5000

6000

7000

8000

0 0.5 1


Fo

rc

e [

N]

Smooth seal- Theory


Grooved seal-Theory


0

1000

2000

3000

4000

5000

6000

7000

8000

0 0.5 1


Force [N

]

Smooth seal- Theory


Grooved seal-Theory


0

1000

2000

3000

4000

5000

6000

7000

8000

0 0.5 1


Fo

rce [

N]





-150

-100

-50

0

50

0 0.2 0.4 0.6


Dam

pin

g [

kN.s

/m]

CXY

0

1000

2000

3000

4000

5000

6000

7000

8000

0 0.2 0.4 0.6 0.8


Fo

rce

[N]

Smooth seal- Theory


Grooved seal-Theory


0

1000

2000

3000

4000

5000

6000

7000

8000

0 0.2 0.4 0.6 0.8


Forc

e [N

]

Smooth seal- Theory


Grooved seal-Theory


0

1000

2000

3000

4000

5000

6000

7000

8000

0 0.5 1


Fo

rc

e [

N]

Smooth seal- Theory


Grooved seal-Theory


0

1000

2000

3000

4000

5000

6000

7000

8000

0 0.5 1


Force [N

]

Smooth seal- Theory


Grooved seal-Theory


0

1000

2000

3000

4000

5000

6000

7000

8000

0 0.5 1


Fo

rce [

N]





0

5001000

1500

2000

25003000

3500

4000

0 1





Oil Seal Cross Damping

Small cross-damping, test data shows

larger magnitude than predictions

Smooth Seal

Grooved Seal

Smooth Seal

Grooved Seal

CYX

CXY

10,000 rpm, 70 bar

(cg= 15c)

(c = 7c)

Figure 12

26


0

5

10

15

20

25

30

35

40

0 0.1 0.2 0.3 0.4 0.5 0.6


Ad

de

d M

as

s [

kg

]

0

5

10

15

20

25

30

35

40

0 0.1 0.2 0.3 0.4 0.5 0.60

5

10

15

20

25

30

35

40

0 0.1 0.2 0.3 0.4 0.5 0.6

0

5

10

15

20

25

30

35

40

0 0.1 0.2 0.3 0.4 0.5 0.6

Test data shows large added mass coefficients.

Predictions correlate well with experimental results.

Added mass coefficients are larger for grooved seal

Classical theory (*) predicts ~ 1/10 of test

value

[1] Reinhardt, F., and Lund, J. W., 1975, “The Influence of Fluid Inertia on the Dynamic

Properties of Journal Bearings,” ASME J. Lubr. Technol., 97(1), pp. 154-167.

MXX

0

5001000

1500

2000

25003000

3500

4000

0 1





Smooth Seal

Grooved Seal

(cg= 15c)

(c = 7c)

Oil Seal Added Mass 10,000 rpm, 70 bar

Figure 13

27


• Good correlation for direct force coefficients for the lower journal eccentricities (e/c=0,0.3) and moderate to good correlation for e/c=0.5.

• Cross-coupled stiffnesses also predicted accurately for the smaller eccentricities. FE model accurately predicts the reduction of the direct stiffness, direct damping, and cross-coupled stiffness coefficients when adding a circumferential groove to the seal land.

• Added mass coefficients for both seals (smooth and grooved) are also predicted accurately (within 20 %). Both analysis and test results show a grooved seal has larger direct added mass coefficient than a smooth seal.

Conclusions:

28


• Discrepancies between test results and predictions for large journal eccentricities (e/c)~0.70. Discrepancies due to (unknown) changes in seal clearance and oil viscosity induced by thermal effects.

• Current model is a significant improvement over prevailing predictive tools to analyze grooved oil seals.

• Deep grooves do not fully uncouple parallel film lands!!

• Model applied successfully to grooved SFDs (+ additional experimental verifications)

Conclusions:

29


Thanks to TAMU Turbomachinery Research Consortium

Acknowledgments

Questions (?)

Learn more at http://rotorlab.tamu.edu

© 2011 Luis San Andres

30

Grooved Oil Seals: Force CoefficientsGT2011-45274Prediction: pressure fields for oil seal without inner groove

Journal whirl motion with r=5 m, =200 Hz)

(b) Current – central groove interacts with film lands

(a) Classical:central groove dyn. pressure = 0

31


Journal whirl motions with r=5 m, =200 Hz)

Prediction: pressure fields for oil seal with inner groove

(a) Classical:central groove dyn. pressure = 0inner land dyn. pressure = 0

(b) Current – central groove and inner groove interacts with film lands

Grooved Oil Seals: Force Coefficients GT2011-45274 1 A Novel Bulk-Flow Model for Improved...

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