t response of a squeeze film damper to impact … trc san...impact load amplitude. with piston rings...
TRANSCRIPT
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
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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