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Sung-Hwa Jeung Graduate Research Assistant

33 rd Turbomachinery Research Consortium Meeting. On the Forced Performance of a SFD Operating with Large Amplitude Orbital Motions: Measurements and Assessment of the Accuracy of the Linearized Force Coefficients Model. TRC-SFD-01-2013. Luis San Andrés Mast-Childs Professor. Sung-Hwa Jeung

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Sung-Hwa Jeung Graduate Research Assistant

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  1. 33rd Turbomachinery Research Consortium Meeting On the Forced Performance of a SFD Operating with Large AmplitudeOrbital Motions: Measurements and Assessment of the Accuracy of the Linearized Force Coefficients Model TRC-SFD-01-2013 Luis San Andrés Mast-Childs Professor Sung-Hwa Jeung Graduate Research Assistant May 2013 TRC Project 32513/1519SF Linear Nonlinear Force Coefficients for SFDs

  2. oil inlet Feed groove SFD with a central groove • Lubricant supplied into a circumferential groove feeds uniformly the squeeze film lands. • Whirl motion from the journal squeezes the lubricant film and generates dynamic pressures that aid to damp the rotor vibrations Typical squeeze film damper (SFD) with a central groove [1] Conventional knowledge regards a groove as indifferent to the kinematics of journal motion, thus effectively isolating the adjacent film lands.

  3. SFD Test Rig – cut section Test Journal Bearing Cartridge Piston ring seal (location) Circumferential groove Supply orifices (3) Main support rod (4) Flexural Rod (4, 8, 12) Journal Base Pedestal in

  4. SFD Test Rig – cut section

  5. Lubricant flow path ISO VG 2 oil Oil inlet in

  6. Funded TRC (2012-13) $ 28,470 • Test damper with dynamic loads (20-300 Hz) inducing off-centered elliptical orbital motions to reach 0.8c. • Identify SFD force coefficients from test impedances, and correlate coefficients with linear force coefficients and experimental coefficients for smallest whirl amplitude (0.05c). • Perform numerical experiments, similar to the physical tests, to extract linearized SFD force coefficients from the nonlinear forces. Quantify goodness of linear-nonlinear representation from an equivalence in mechanical energy dissipation.

  7. Tests conducted Excitation frequencies 10 – 100 Hz Evaluate SFD dynamic force coefficients from Circular orbit journal motions with orbit amplitudes (r) from 8% to 71% of radial clearance (c). Static journal eccentricity (e)to 76% of radial clearance (c). Max. clearance (c) : 251μm Y es = 0.76 c es = 0.51 c es = 0.25 c X Y Displacement [μm] es= 0 c X Displacement [μm]

  8. Parameter identification procedure Step 1 : Model system (2-DOF) F Shaker force EOM: Time Domain ML KL CL EOM: Frequency Domain Measured variables: KL, CL, ML Unknown Parameters: SFD coefficients • (K, C, M)SFD = (K, C,M)L – (K, C, M)S • Test system • (lubricated) • SFD • Structure

  9. Test SFD damping coefficients Y = 0.76 c = 0.51 c = 0.25 c X = 0 c CXX SFD eS=0.76c eS=0.25c eS=0.51c eS=0.0c (eS/c) CXX~CYY Findings: SFD damping coefficients increase with increasing orbit amplitude and static eccentricity. CXXincreases dramatically above r/c > 50%

  10. Y = 0.76 c = 0.51 c = 0.25 c X = 0 c Test SFD added mass coefficients MXX SFD eS=0.76c eS=0.51c eS=0.25c eS=0.0c (eS/c) MXX~MYY Findings: SFD added mass coefficients increase with increasing static eccentricity; but decrease with increasing orbit amplitude. MXXdecreases dramatically above r/c>50%

  11. SFD effective force coefficients For circular orbits (only),SFD forces reduce to Y -Fradial rw X r -Ftangential

  12. Test SFD effective stiffness • -Keff • structure es/c=0.0 Findings:SFD effective stiffness decreases with increasing excitation frequency and with orbit amplitude (a fluid inertia effect).

  13. Test SFD effective damping • Ceff es/c=0.0 Findings: SFD effective dampingincreases with orbit amplitude. Little dependency with frequency.

  14. Pressure sensors in housing 14

  15. Film dynamic pressure profiles es/c=0.0, 100 Hz Magnitude of peak pressure increases with orbit amplitude. Central groove Film lands Top and bottom film lands show similar pressures. Dynamic pressure in the groove is not nil. Air ingestion region

  16. Film dynamic pressure profiles A uniform pressure zone indicates air entrainment.

  17. Model SFD with a central groove SFD geometry and nomenclature Use effective depth Solve modified Reynolds equation (with temporal fluid inertia) h: fluid film thickness P: hydrodynamic pressure μ: lubricant viscosity R: journal radius

  18. Damping: predictions and test data Y 45o for small size orbits (r/c=0.08). predictions agree with test coefficients until es=0.5 c. At es/c=0.76 predictions are too large (~28%) c es X classical theory (1.2 kN.s/m) Test data much larger than simple theory CXX CYY Test data Test data Model by San Andres (2011) Prediction Prediction

  19. Added mass: predictions & test data Y 45o es X c Model predictionsagree well with experimental results. Predicted added masses increase slightly with static eccentricity classical theory (1.67 kg) Test data much larger than simple theory MXX MYY Model by San Andres (2011) Test data Test data Prediction Prediction

  20. SFD mechanical energy dissipation • SFD reaction forces Actual force Linearized force • Mechanical work • Over a full period of motion

  21. Work=Energy dissipation 100 Hz EDIS<0 is negative work = energy dissipated by SFD Findings: SFD work increases with increasing orbit amplitude.

  22. Mechanical energy difference 100 Hz 0~5% ~23% Findings: Energy difference increases with increasing static eccentricity and orbit amplitude. For r/c≤0.4 andes/c≤0.25, Ediff < ~5%

  23. Conclusions From circular orbit tests (a) SFD damping coefficients increase with increasing orbit amplitude and static eccentricity. (b) SFD added mass coefficients increase with increasing static eccentricity and decrease with increasing orbit amplitude. Predictions correlate very well with test results for static eccentricity es<0.5c and deviate with increasing orbit amplitude and static eccentricity. Goodness of linear force model By means of comparing mechanical work in a period of motion; forr/c≤0.4 and es/c≤0.25, linearized SFD forced parameters represent well the actual SFD system TRC-SFD-01-2013

  24. 2013 proposal to TRC Justification Aircraft engines must endure sudden maneuver loads (blade loss event, etc.) Large size grinding machines require quick dissipation of mechanical energy from sudden plunging motions (tool contacts the working piece, etc.) Ultra-short SFD (L/D < 0.2) save space & weight; with lighter lubricants to save fuel and reduce contamination; and with tighter clearances because of better materials & manufacturing.

  25. 2013 proposal to TRC • Objectives • Conduct experiments to characterize the forced response of a short length SFD (L/D=0.2) with sudden loads (400 lbf max). • Build predictivetool to simulate SFD dynamic forced performance. Record SFD forced performance due to sudden impulsive loads (amplitude and time varying). Sudden load

  26. TRC Budget 2013-2014 Year III The TAMU SFD research program is the most renown in the world. The proposed research is of interest of SFD applications in gas turbines, hydrodynamic bearings in compressors, cutting tool and grinding machines.

  27. Learn more at http://rotorlab.tamu.edu Thank you Acknowledgments Thanks to TAMU Turbomachinery Research & Pratt & Whitney Engines Questions (?) 27

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