T RESPONSE OF A SQUEEZE FILM DAMPER TO IMPACT … TRC San...impact load amplitude. With piston rings . Open ends . 12 Peak displacement vs load Peak BC displacement is proportional

Luis San Andrés Mast-Childs Chair Professor

STLE Fellow Texas A&M University

Sung-Hwa Jeung Compressor Design Engineer

Ingersoll Rand

Bonjin Koo Graduate Research Assistant

Texas A&M University

Proceedings of STLE Annual Meeting & Exhibition, May 20-24, 2018 Minneapolis Convention Center, Minneapolis, Minnesota, USA

Supported by Pratt & Whitney Engines and Turbomachinery Research Consortium

TRANSIENT RESPONSE OF A SQUEEZE FILM DAMPER TO IMPACT LOADS: EXPERIMENTS

AND PREDICTIONS

2

Aid to attenuate rotor vibrations, suppress rotor instabilities, and

provide mechanical isolation.

Too little damping may not be enough to reduce vibrations. Too much damping may lock damper & will degrade system

rotordynamic performance.

Squeeze Film Dampers (SFDs)

Lubricant film

Shaft

Ball bearing

Anti-rotation pin

Journal

Housing

Often coupled with bearings that lack damping or have

too large stiffness.

SFDs are designed with consideration of the entire rotor-bearing system.

3

Piston ring seals Piston ring

seals

Piston ring seals

No end grooves

To explore novel SFD designs & benchmark

SFD empirical data.

Develop & validate SFD force

performance model..

Optimize SFD influence on

rotor dynamics. 20+ papers

Multiple-year test program (2008- 2018)

4

Brief literature review

Tichy and Bou-Said (1991)

Fluid inertia effect under an impulsive load

A numerical case study: fluid inertia apparent force leads to a reduction in journal peak amplitude of motion.

Lee et al. (2006) Transient response of a rotor-bearing system is sensitive to the time duration of the external shock. San Andrés and Jeung (2015) SFD impact load tests: (amplitude motion/load amplitude)~ constant system damping ratio increases with amplitude of motion, i.e. applied load amplitude.

5

SFD Test Rig

Static loader

Shaker in X direction

Shaker in Y direction

Top view

SFD test bearing

2 electro magnetic-shakers (2 kN ~ 550 lbf) Static loader placed 45°between X and Y axes Customizable SFD test bearing.

6

SFD Test Rig – cut section

7

Reduce flow rate and side leakage to rise film dynamic pressures and increase damping coefficient.

Piston ring design as an end seal is highly empirical.

Piston rings Lubricant

Leakage

Film

Housing Journal

while also reducing air ingestion.

Piston rings as end seals

8

Oil inlet temperature, Ts = 23 oC Density, ρ = 800 kg/m3

Viscosity μ at Ts= 2.6 cPoise

ISO VG 2 oil

Lubricant flow path

in

Oil inlet

9

Oil flow rate vs. supply pressure

Piston rings effective to reduce side leakage.

With piston rings

Open ends

10

Transient response due to a single impact load

Impa

ct

Time

11

Transient motion decays fast for PR sealed SFD

Impact load bearing displacement

Increase in impact load amplitude

With piston rings

Open ends

12

Peak displacement vs load

Peak BC displacement is proportional to

magnitude of impact load:

( )β→

dynMAX

MAX

Z cF L D

With piston rings

Open ends

Static eccentricity varies

13

β ~ constant with an increase in static eccentricity. Open ends damper shows twice larger β than PR sealed SFD.

Single impact

β : Peak amplitude/load vs static eccentricity X direction

( )β→

dynMAX

MAX

Z cF L D

With piston rings

Open ends

14

Damping ratio and log dec

2

21

πζδζ

=−

Logarithmic decrement

Response of a viscous underdamped system

2ζ =

S

CK Mω = S

nKM

( ) ( cos sin )ζω ω ω−= +ntd dZ t e A t B t

21d nω ω ζ= −

= +BC SFDM M M

15

The BC transient response

for PR-SFD decays faster than that of OE-

SFD. damping ratio

increases.

Transient response damping ratio

With piston rings

Open ends

16

Damping ratio & vs peak displacement

PR-SFD has a large damping

ratio (ξ ~ 0.6 0.8)

Open ends SFD has + lesser

damping ratio ( ξ ~ 0.03 0.1)

though increasing with

amplitude (ZMAX).

ZMAX = ZSTAT + ZDYN

With piston rings

Open ends

17

Comparisons of experimental damping ratio to predictions from physical model

18

Model SFD with fluid inertia – centered motion

Equation of motion for test system with rigid mass:

Dynamic pressure field P governed by extended Reynolds equation:

SFD reaction force:

BC s s SFD extM C K+ + = +r r r F F

{ },X Yr r= Tr is a journal displacement vector.

( ) ( ) ( )0 0

23 2

212 cos sinX Y X Yh hh P h h c e e r rt t

µ ρ∂ ∂∇ ∇ = + ← = + + − Θ − Θ

∂ ∂

( )22

, ,02

cossin

LX

SFD z tLY

FP Rd dz

Fπ

Θ−

Θ = = − Θ Θ

∫ ∫F

+ X

Y

Θ h r

19

Transient response: predicted and measured Findings:

POOR AGREEMENT.

-1-0.8-0.6-0.4-0.2

00.20.40.60.8

1

0 20 40 60 80 100Time (msec)

Z (t)/

Z MA

X, [

-]

-1-0.8-0.6-0.4-0.2

00.20.40.60.8

1

0 20 40 60 80 100Time (msec)

Z (t)/

Z MA

X, [

-]

ζ = 0.43 ωn = 87 Hz

Open ends

Sealed ends

Prediction:

ζ = 0.65 ωn = 83 Hz

Test data:

Prediction:Test data:

FMAX/(LD)=1.7 bar

FMAX/(LD)=1.6 bar

Damping envelope ( )

Predictionnte ξω−Test data

CSFD = 0.9 kN-s/m, MSFD = 0.6 kg

CSFD = 15.7 kN-s/m, MSFD = 18.2 kg

ζ = 0.04ζ = 0.04

ωn = 127 Hzωn = 116 Hz

With piston rings

Open ends

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Conclusions

(a) Sealed ends SFD shows a larger decay in response compared to open ends SFD larger effective damping.

(b) Sealed ends SFD has a smaller natural frequency than open ends SFD significant fluid inertia.

(c) For open ends SFD, system damping ratio (ζ) increases linearly with LOAD magnitude peak displacement ZMAX.

(d) While the sealed ends SFD shows more or less constant damping ratio with increasing peak displacement ZMAX.

Transient response due to a single impact load

21

Thanks to • Pratt & Whitney Engines

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

Questions (?)

• TAMU Turbomachinery Research Consortium

Acknowledgements