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ASME GT2009-59175

2009 ASME Turbo Expo Conference, June 2009. I DENTIFICATION of SQUEEZE FILM DAMPER FORCE C OEFFICIENTS from MULTIPLE-FREQUENCY NON-CIRCULAR JOURNAL MOTIONS. Luis San Andrés Mast-Childs Professor Texas A&M University. Adolfo Delgado Mechanical Engineer GE Global Research Center.

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ASME GT2009-59175

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  1. 2009 ASME Turbo Expo Conference, June 2009 IDENTIFICATION of SQUEEZE FILM DAMPER FORCE COEFFICIENTS from MULTIPLE-FREQUENCYNON-CIRCULAR JOURNAL MOTIONS Luis San Andrés Mast-Childs Professor Texas A&M University Adolfo Delgado Mechanical Engineer GE Global Research Center ASME GT2009-59175 accepted for journal publication Supported by TAMU Turbomachinery Research Consortium

  2. anti-rotation pin shaft journal ball bearing w lubricant film housing Typical squeeze film damper (SFD) configuration SFD Operation & Design Issues In aircraft gas turbines and compressors, squeeze film dampers aid to attenuate rotor vibrations and to provide mechanical isolation. Too little damping may not be enough to reduce vibrations. Too much damping may lock damper & degrades system rotordynamic performance In a SFD, the journal whirls but does not spin. The lubricant film is squeezed due to rotor motions, and fluid film (damping) forces are generated as a function of the journal velocity.

  3. anti-rotation pin shaft journal ball bearing w lubricant film housing Typical squeeze film damper (SFD) configuration SFD Operation & Design Issues • Damper performancedepends on • Geometry (L, D, c) • Lubricant (density, viscosity) • Supply pressure and through flow • Sealing devices • Operating speed (frequency) • Flow regimes: (laminar, superlaminar, turbulent) • Type of lubricant cavitation: • gaseous or vapor • air ingestion & entrapment

  4. Intershaft Dampers In multi-spool engines, intershaft dampers are located in the interface between rotating shafts Multiple frequency excitation. HP shaft Intershaft dampers are subject to whirl motions resulting from the combined imbalance response of both the LP and the HP shafts. Objective: to investigate the forced performance of SFD for non-circular motions with multi-frequencies LP shaft Schematic view of intershaft [*] [*] Gupta K., and Chatterjee S., 2007, “Dynamics of an Improved Inter Shaft Squeeze Film Damper: Theory and Experiment,” ASME paper No. GT2007-27534.

  5. Relevant Past Work Intershaft SFDs • Della Pietra and Adilleta (2002):Comprehensivereview of research conducted on SFDs over last 40 years. • (1975) Hibner • (1991) Al-Shafei • (2008) Defaye et al. Parameter identification in SFDs: • Tiwari et al. (2004):Comprehensivereview of parameter identification in fluid film bearings. • (1986) Roberts et al, • (1990) Ellis et al. , • (1999) Diaz and San Andrés • (2006-2008) San Andrés and Delgado (SFD & MECHANICAL SEAL) GT 2006-91238, GT 2007-24736, GT 2008-50528

  6. Schematic view of test rig Bearing Assembly TRC SFD Vertical Test Rig

  7. Oil inlet Eddy current sensor Plexiglas Bearing Housing Top plate Vertical plate O-rings Discharge groove O-rings Bottom plate Ring carrier Discharge orifice Journal Pipe insert Shaft SFD bearing design Open end configuration L=25.4 mm, D=127 mm, c=0.127 mm (5 mil)

  8. Flow through squeeze film land Feed plenum Inlet groove Squeeze film land Discharge groove Clearance c= 0.127 mm (5 mil) Diameter D = 127 mm (5 inch) Length L = 25.4 mm (1 inch) ISO VG 2 oil Open End Configuration

  9. Multiple frequency excitations ISO VG 2 Feed pressure= 31 kPa Temperature (avg.)= 24 0C Max. clearance: 127 mm 130 65 Multiple frequency excitation force: Low speed shaft: fixed frequency (25 Hz) Y Displacement [mm] + -65 -130 65 130 High speed shaft: sine sweep (30 Hz to 120 Hz) Three excitation vectors: Case 1 Low and high speed shafts in phase Case 2 Low and high speed shafts 90 deg out of phase Case 3 Excitation vector amplitude increases (constant amplitude response) -65 -130 X Displacement [mm]

  10. Parameter Identification Non-circular whirl motions Equations of motion SFD coefficients (function of instantaneous journal eccentricity e) Added mass coefficient constant for test journal amplitudes (< 60% c) For parameter identification only 1x componentis considered (dissipates mechanical energy) Dissipative non-linear force function of journal position e and velocity v

  11. Parameter Identification For each excitation force frequency component (sine sweep) From two independent vectors with Hii1 = Hii2 ; i=x,y Damping coefficients Dynamic stiffnesses

  12. Linear sweep Fixed frequency Excitation Force & Displacement Case 1 Clearance: 127 mm Highly elliptical motions 130 65 Y Displacement [mm] -65 65 130 Time trace (Force) -65 -130 X Displacement [mm] Case 1: LS & HS in phase

  13. Single Frequency + Sine sweep 25 Hz Identification Range Parameter xx yy Identified Mass, ( M) 16.3 kg 16.1kg Squeeze film inertia ( M ) 6.1 kg 5.9 kg SFD 2 r (goodness of curve fit) 0.97 0.98 Added mass coefficient from 6.6 kg Parameter Identification Case 1 FREQUENCY DOMAIN Dynamic stiffness Force Identification Range Re(Hxx)= Kxx-Mxxw2 Displacement [1] Classical theory predicts = 2.1 kg (3 times smaller) [1] Delgado, A., 2008, “A Linear Fluid Inertia Model for Improved Prediction of Force Coefficients in Grooved Squeeze Film Dampers and Grooved Oil Seal Rings,” Ph.D. Dissertation, December, Texas A&M University, C/S, TX. Frequency spectra

  14. Parameter Identification Case 1 Damping coefficient Predictions (small radial motions about an off-centered position) Predictions (circular centered orbits) Im(Hxx/w) e Damping coefficient [kN.s/m] Damping coefficients bracketed by predictions from full film short length SFD model (open ends) Cross-coupled coefficients negligible (No lubricant cavitation) Amplitude/clearance

  15. Linear sweep Fixed frequency Excitation Force & Displacement Case 2 clearance: 127 mm Non circular whirl motions 130 65 Y Displacement [mm] -65 65 130 Time trace (Force) -65 -130 X Displacement [mm] Case 2: LS & HS out of phase

  16. Parameter Identification FREQUENCY DOMAIN Case 2 Dynamic stiffness Force Re(Hxx)= Kxx-Mxxw2 Displacement Similar added mass coefficients as in Case 1 Frequency spectra

  17. Parameter Identification FREQUENCY DOMAIN Case 2 Im(Hxx/w) Damping coefficient e For excitation loads (Fx, Fy) out of phase by 90 degree, identified damping coefficients are closer to predictions for circular (centered) motions Damping coefficient [kN.s/m] Case 2: LS & HS out of phase Amplitude/clearance

  18. Excitation Force & Displacement Case 3 Similar to case 2 but with increasing amplitude of excitation load 3 constant motion amplitudes ~20 um, ~40 um, ~ 60 um Case 3: LS & HS out of phase

  19. Damping coefficient Im(Hxx) ~ 60 um e Im(Hxx) ~40 um Damping coefficient [kN.s/m] Im(Hxx) Amplitude/clearance ~20 um Linear (single) damping coefficient Case 3: LS & HS out of phase

  20. SFD force coefficients could be identified for multiple-frequencies when expressed as generic functions of journal position and velocity. The motion with amplitude at main excitation frequency is one that leads to dissipation of mechanical energy. Classical SFD (open ends) model predictions: centered circular orbits and small amplitude motions about off-centered position ENCLOSE the identified damping coeffs. Novel model added mass coefficient correlates well with test data. Classical theory predicts mass coefficients 3 times smaller than test values. Large mass due to effects of inlet and discharge grooves. Conclusions:

  21. Thanks to TAMU Turbomachinery Research Consortium Acknowledgments Learn more athttp://phn.tamu.edu/TRIBGroup Questions ?

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