May 2017 Year V E FFECT OF L UBRICANT S UPPLY P RESSURE ON SFD P ERFORMANCE : E NDS S EALED WITH O- RINGS & P ISTON R INGS TRC-SFD-01-17 Luis San Andrés Bonjin Koo Leping Yu Mast-Childs Chair Professor Graduate Research Assistants
Squeeze Film Damper (SFDs) Whirling motion from the journal squeezes the lubricant film and generates dynamic pressures that provides viscous damping to decrease rotor vibrations Aid to reduce rotor vibrations, suppress system instabilities, and provide mechanical isolation. Too little damping may not be enough to reduce vibrations. Too much damping may lock damper & will degrade system performance. 2
SFD Test Rig Structural stiffness (Rods), K S =1.6 MN/m , O-ring stiffness, K O-ring =0.6 MN/m, K S+O-ring =2.2MN/m Bearing cartridge mass, M BC =15 kg 3
Journal geometry and lubricant properties Short length SFD L / D =0.2 Piston ring seals Supply orifices Geometry Journal Diameter, D 127 mm (5.0 in) Land Length, L 25.4 mm (1.0 in) Lubricant Properties 373 μm (14.7 mil) Radial Land Clearance, c Lubricant Type ISO VG 2 Feed orifice Diameter, ϕ Supply temperature, T in 23 °C (73 °F) 2.54 mm (0.1 inch) Lubricant viscosity @ T in , μ Feed orifice location 45º 2.57 cP End groove width 2.5 mm Lubricant density, ρ 820 kg/m 3 End groove depth 3.8 mm 4
PR-SFD: Piston rings as end seals Leakage θ =90° PR slit Y Static Loader ( θ =135 o ) θ =45° Piston Housing Journal ring (PR) θ =0° Bearing Film Lubricant X Cartridge Feedhole Piston rings Journal (a) Piston ring Piston ring geometry Outer diameter 127 mm Thickness 3.3 mm Width 2.5 mm Material Steel Outer diameter: 127 mm Thickness: 3.3 mm 5
OR-SFD: O-rings as end seals θ =90° No leakage Y Journal Feedhole Housing O-ring ( φ =2.3 mm) Journal θ =0° X Lubricant Discharge Discharge hole Bearing ( φ =2.0 mm) Cartridge Film (b) O-ring Steel O-rings spacer O-ring geometry Diameter 120 mm Thickness 2.6 mm Diameter: 120 mm Material Buna-N Thickness: 2.6 mm 6
Test Procedure Step 1: Apply loads and measure BC motions Apply forces by shakers Y Y CW 1 2 F F ω ω = = 1 i t 2 i t X X F Re F Re e e − 1 2 iF iF X X Y Y CCW Record BC displacement z and acceleration a 1 2 1 2 x x X X ω ω = = = = 1 (t) i t 1 2 (t) i t z a z e e 2 a 1 2 1 2 y y Y Y (t) (t) EOM: Frequency domain Find parameters: + ω − ω = − → = − ω + ω 2 2 [ K i C M ] z F M a H K M i C L L L L L L L BC 7
c =373 µ m, orbit size r / c =0.3 Test Procedure Step 2: Curve fit H L ’s using KCM model (K, C, M) SFD = (K, C,M) L – (K, C, M) S Test system SFD Film Dry (Lubricated) structure ( ) ( ) − − − → − ω − → ω 1 2 1 Re [ F M a z ] K M Im [ F M a z ] C BC L L BC L Test data Test data Model fit Model fit Test data Model fit H XX H XX H XX P s = 1.4 bar P s = 3.5 bar P s = 6.2 bar H YY H YY H YY 8
OR-SFD damping and mass vs. supply pressure θ =90° Y Journal Feedhole O-ring P s >2.0 bar, C avg and M avg remain at ( φ =2.3 mm) ~ 11kN-s/m and ~30 kg, respectively. θ =0° X P s <2.0 bar, C avg ↓ as P s ↓ . Discharge hole Bearing ( φ =2.0 mm) Cartridge c =373 µ m, r / c =0.3, ω =10-100 Hz 9
OR-SFD & PR-SFD C and M vs. supply pressure c =373 µ m, r / c =0.3, ω =10-100 Hz - Damping C avg for OR-SFD is 11% larger than C avg for PR-SFD. - Added mass M avg ~30 kg as supply pressure decreases. - Damping coefficients C avg ↓ as lubricant supply pressure ↓ . 10
c =373 µ m, r / c =0.3 Peak film pressure vs. freq PR-SFD OR-SFD Peak-peak dynamic pressure [bar] r/c =0.3 Peak-peak dynamic pressure [bar] r/c =0.3 P s = 0.7 bar P s = 0.7 bar P s = 3.5 bar P s = 3.5 bar P s = 6.2 bar P s = 6.2 bar Air ingestion Air ingestion Frequency [Hz] Frequency [Hz] For P s =0.7 bar, and whirl freq. > 60 Hz, peak-to-peak dynamic pressure stops growing (due to air ingestion). 11
PR-SFD pressure profiles r / c =0.3, ω = 90 Hz Pressure profiles for P s = 0.7 bar P s =3.5 and 6.2 bar are almost identical. Spikes in pressure P s = 2.1 bar may be due to bursts of leakage thru PR slits. P s = 3.5 bar P s = 6.2 bar 12
OR-SFD pressure profiles r / c =0.3, ω = 90 Hz Pressure profiles P s = 0.7 bar for P s =3.5 and 6.2 bar are ~ identical. There are no sharp P s = 2.1 bar spikes on pressure. θ =90° Y P s = 3.5 bar O-ring θ =0° X P s = 6.2 bar P 4 ( θ =225 o ) Measured Discharge point hole ( φ =2.0 mm) 13
Sudden loss of flow Tests conducted with SFD operating (under dynamic load) with amplitude r= 0.2 c . Pressure supply (flow rate) is set. At time t= 0 s, flow (pressure) is cut off. Ensuing motions recorded as squeeze action expels remnant lubricant in film. 14
Test rig time response P s =Q s = 0.0 at t > 0 P s =3.5 bar, Q s =2.4 LPM P s =6.2 bar, Q s =3.0 LPM Clearance Clearance PR-SFD Displacement, Y ( µ m) Displacement, Y ( µ m) θ =90° Feedhole Y ( θ =45 o ) PR slit ( θ =135 o ) θ =0° X Out of sensor range Out of sensor range Displacement, X ( µ m) Displacement, X ( µ m) P s =6.2 bar, Q s =6.0 LPM P s =3.5 bar, Q s =3.5 LPM OR-SFD Clearance θ =90° Y Feedhole Displacement, Y ( µ m) ( φ =2.3 mm) θ =0° Recorded time X 0 sec Jump & 1 sec 2 sec Discharge static 3 sec O-ring hole 4 sec offset 5 sec ( φ =2.0 mm) Displacement, X ( µ m) 15
WATERFALLs of motion P s =Q s = 0.0 at t > 0 PR-SFD P s =3.5 bar, Q s =2.4 LPM θ =90° Feedhole Y ( θ =45 o ) PR slit ( θ =135 o ) θ =0° X Jump & OR-SFD static offset P s =3.5 bar, Q s =4.5 LPM θ =90° Y Feedhole ( φ =2.3 mm) θ =0° X Discharge O-ring hole ( φ =2.0 mm) 16
Conclusion • Both O-ring and piston-ring sealed ends SFDs show similar damping and added mass coefficients. For a large supply pressure ( P s ) performance of a sealed ends • SFD does not change with an increase in squeeze film velocity ( V s = r ω ). • Too low oil feed pressure reduces film pressure and damping. • A sudden loss of flow causes immediate changes in performance: (a) For PR-SFD, whirl orbit motion increases in amplitude (w/o bound) to show collapse of element (to touch clearance). (b) For OR-SFD, whirl motion at t= 0 jumps (static offset) and later shows growth. O-ring resilience keeps motions bounded 17
Acknowledgments Turbomachinery Research Consortium & Pratt & Whitney Engines Questions (?)
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