Response of an Open Ends Squeeze Film Damper to Large Amplitude Impact Loads

Transcription

1 2015 STLE Annual Meeting & Exhibition, May 17-21, 2015, Dallas, TX Response of an Open Ends Squeeze Film Damper to Large Amplitude Impact Loads Luis San Andrés Mast-Childs Chair Professor Fellow STLE Sung-Hwa Jeung Graduate Research Assistant 19 May :30 pm Supported by P&W Engines and TAMU Turbomachinery Research Consortium 1

2 Squeeze Film Dampers (SFD) anti-rotation pin journal ω lubricant film shaft ball bearing housing oil inlet Feed groove 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 SFDs attenuate rotor vibrations and provide mechanical isolation. Often coupled with other type of bearing that lacks damping or has a too large stiffness. 2

3 SFD operation & design Too little damping may not be enough to reduce vibrations. SFD with dowel pin Too much damping may lock damper & degrade system rotordynamic performance Efficient designs save space, weight lower cost. X Y Misconceptions about fluid inertia and stiffness. SFDs can have a significant effect on system critical speeds. 3

4 SFD Test Rig cut section Test Journal Bearing Cartridge Piston ring seal (location) Supply orifices (3) Main support rod (4) Flexural Rod (4, 8, 12) Journal Base Pedestal in 2 e-shakers (550 lbf) Static loader at 45 Customizable SFD section

5 Multiple-year test program ( ) Explore new SFD design & benchmark SFD empirical data. Piston ring seals Piston ring seals No end grooves Piston ring seals Develop and validate SFD forced performance model & improve its predictions. Optimize SFD influence on rotor dynamics. 5

6 Past work with same test rig San Andres and et al. ( ) J. Eng. Gas Turbines and Power, 2012, 134. J. Eng. Gas Turbines and Power, 2013, 135. STLE Annual meeting, Detroit, Tribology International, 2014, 71. IFToMM Conference, Italy, 2015 (Best Paper Award) Orbit amplitude, r/c Comparing force coefficients for dampers B and C shows that a deep feed groove has little effect on the film damping (C SFD ), but increases its inertia (M SFD ). J. Eng. Gas Turbines and Power, 2015, 137. GT GT Configuration w/o groove saves space and weight. 6

7 ISO VG 2 Lubricant flow path ISO VG 2 oil Oil inlet in Supply temperature, T in 23 C (73 F) Lubricant T in, μ 2.6 cp Lubricant density, ρ 800 kg/m 3 7

8 SFD Test Rig cut section Short length SFD Geometry (three feed holes 120o apart) Journal Diameter, D 12.7 cm (5.0 in) Land Length, L 2.54 cm (1.0 in) Radial Land Clearance, c 213 μm (8.4 mil) Feed orifice Diameter, ϕ 2.54 mm (0.1 inch) L/D=0.2 8

9 Tests conditions Evaluate SFD dynamic force response from: Impact loads to cause large amplitude motions (max 93% of radial clearance=0.213 mm) Initial state: centered and static Motion Type Number of impacts Max. load amplitude, F MAX (kn) Peak amplitude, Z MAX (μm) Unidirectional

10 Impact load and bearing displacement Motion is transient and decays fast. Max. displacement [Z MAX /c] Unit load, F MAX /(LD) [bar] R 2 XX=0.98 e s /c=0.0 R 2 YY=0.99 X-direction Y-direction Max. impact force F MAX [kn] 10

11 Transient response damping ratio Findings: The higher the impact load, the fastest the decay. Damping ratio increases with increasing load 11

12 Damping ratio and log dec Response of a viscous underdamped system n t d d Z() t e ( Acos t Bsin t) n K M S 2 C KM S 1 d n 2 M M M BC SFD Logarithmic decrement

13 Damping ratio and log dec ~ C M Findings: Damping ratio is proportional (linear) to the magnitude of load (and peak BC displacement). 13

14 Parameter identification procedure Step 1 : Model system (2-DOF) EOM: Time Domain F Shaker force K L C L M L EOM: Frequency Domain 2 [ L i L L] MBC K C M z F a Measured variables: Unknown Parameters: K L, C L, M L 14

15 SFD force coefficients Step 3 : Transform to frequency domain and curve fit impedance Instrumental Variable Filter Method (Fritzen, 1985, J.Vib, 108) Impedance (Frequency Domain) F M 1 2 BCa z KL M 1 Im [ M ] L BC Re [ ] F a z C L F MAX =0.6 kn Z MAX /c=0.14 SFD coefficients (K, C, M) SFD = (K, C,M) L (K, C, M) S SFD Test system (lubricated) Structure 15

16 Test SFD damping coefficients CXX SFD CYY SFD Findings: SFD direct damping increases with peak displacement amplitude (or applied load). C XX increases more for Z/c > 60%. SFD cross-coupled damping (C XY,C YX ) are negligible. 16

17 Test SFD added mass coefficients MXX SFD MYY SFD Findings: SFD direct added mass (M XX,M YY )increasewith bearing peak amplitude.atz/c=0.93, M XX ~6 kg, ~ 4/10 BC mass (15 kg). SFD cross-coupled added masses small. 17

18 SFD force coefficients - theory Short length SFD model Centered journal (e s =0), no oil cavitation Damping C XX D L CYY 2 c 3 Inertia M XX 3 D L MYY 12 c c=213 μm (8.4 mil) μ = 2.6 cp (@ T s =23ºC) L = 25.4 mm (1 in) ρ = 800 kg/m 3 18

19 Predictions and test data - SFD force coeff. Damping Coefficient [kn.s/m] 6 CXX, CYY 5 e s /c= Short length SFD model (0.9 kn.s/m) Maximum displacement [Z MAX /c] Radial clearance c=213μm Added Mass Coefficient [kg] MXX, MYY e s /c=0.0 Short length SFD model (1.0 kg) Maximum displacement [Z MAX /c] Radial clearance c=213μm Test data: X-direction Test data: Y-direction For small amplitude motions (z/c)~0, predictions agree with test coefficients. Prediction: Short length open ends SFD model 19

20 Test SFD force (measured and from coefficients) SFD force constructed from BC motion: Force coefficients : F SFD = F - F s -M BC a... F SFD-LINEAR = M SFD z+ C SFD z+ K SFD z Force from structure... F s = (M S z+ C S z+ K S z) Impact Y direction e S /c=0 Findings: The SFD forces constructed from both the applied force and the recorded motion and estimated force coefficients are in good agreement. 20

21 Conclusions from impact load tests (a) SFD damping (C) and inertia (M) increase with increasing LOAD. The larger the load (BC displacement), the larger the growth rate of the force coefficient. (b) For the fast transient event conditions, crosscoupled force coefficients are small. (c) Damping ratio growths with the amplitude of impact load. Test system damping ratio (ζ~c/m) does not growth as rapidly as C and M. (d) Predictions based on the short length SFD model show good agreement with the test results for small BC amplitudes ONLY (small impacts). 21

22 Acknowledgments Turbomachinery Research Consortium & Pratt & Whitney Engines Turbomachinery Laboratory Staff and Students Questions (?) Learn more at 22