E FFECT OF L UBRICANT S UPPLY P RESSURE ON SFD P ERFORMANCE : E NDS S - - PowerPoint PPT Presentation

EFFECT OF LUBRICANT SUPPLY PRESSURE ON SFD PERFORMANCE: ENDS SEALED WITH O-RINGS & PISTON RINGS

Bonjin Koo Leping Yu

Graduate Research Assistants

Luis San Andrés

Mast-Childs Chair Professor

TRC-SFD-01-17

May 2017 Year V

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.

Squeeze Film Damper (SFDs)

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), KS=1.6 MN/m, O-ring stiffness, KO-ring=0.6 MN/m, KS+O-ring=2.2MN/m Bearing cartridge mass, MBC=15 kg

3

Journal geometry and lubricant properties

Geometry Journal Diameter, D 127 mm (5.0 in) Land Length, L 25.4 mm (1.0 in) Radial Land Clearance, c

373 μm (14.7 mil)

Feed orifice Diameter, ϕ Feed orifice location End groove width End groove depth 2.54 mm (0.1 inch) 45º 2.5 mm 3.8 mm

Short length SFD

Piston ring seals

Lubricant Properties

Lubricant Type Supply temperature, Tin ISO VG 2 23 °C (73 °F) Lubricant viscosity @ Tin , μ 2.57 cP Lubricant density, ρ 820 kg/m3

Supply

• rifices

L/D=0.2

4

PR-SFD: Piston rings as end seals

Y X θ=0° θ=90° Bearing Cartridge Journal Static Loader θ=45° Piston ring (PR) Feedhole PR slit (θ=135o)

Piston rings Lubricant Leakage

Film Housing Journal

Outer diameter: 127 mm Thickness: 3.3 mm (a)

Piston ring

Piston ring geometry

Outer diameter 127 mm Thickness 3.3 mm Width 2.5 mm Material Steel

5

OR-SFD: O-rings as end seals

O-ring geometry

Diameter 120 mm Thickness 2.6 mm Material Buna-N Y X θ=0° θ=90° Bearing Cartridge Journal O-ring Feedhole

(φ=2.3 mm)

Discharge hole

(φ=2.0 mm)

O-rings Lubricant No leakage

Film Housing Journal

Steel spacer Discharge

Diameter: 120 mm Thickness: 2.6 mm (b)

O-ring

6

Test Procedure

Step 1: Apply loads and measure BC motions

1 1 1

Re

i t X Y

F e iF

ω

    =           F

2 2 2

Re

i t X Y

F e iF

ω

    =       −     F

1 1 (t) 1 1 (t) i t

x X e y Y

ω

    = =          

1

z

2 2 (t) 2 2 (t) i t

x X e y Y

ω

    = =          

2

z

2

a

1

a

CW

Y X

CCW

X Y

2

[ ]

BC

i M ω ω + − = −

L L L

K C M z F a

2 L L L

i ω ω → = − +

L

H K M C

Record BC displacement z and acceleration a Apply forces by shakers EOM: Frequency domain Find parameters:

7

Test Procedure

Step 2: Curve fit HL’s using KCM model

c=373 µm, orbit size r/c=0.3

Ps=3.5 bar Ps=1.4 bar Ps=6.2 bar

Test data Model fit HXX HYY HXX HYY HXX HYY Test data Model fit Test data Model fit

(K, C, M)SFD = (K, C,M)L – (K, C, M)S

SFD Film Test system (Lubricated) Dry structure

( )

1

Im [ ]

BC

M ω

−

− →

L

F a z C

( )

1 2

Re [ ]

BC

M ω

−

− → −

L L

F a z K M

8

OR-SFD damping and mass vs. supply pressure

Y X θ=0° θ=90° Bearing Cartridge Journal O-ring Feedhole

(φ=2.3 mm)

Discharge hole

(φ=2.0 mm)

Ps>2.0 bar, Cavg and Mavg remain at ~ 11kN-s/m and ~30 kg, respectively. Ps<2.0 bar, Cavg ↓ as Ps ↓.

c=373 µm, r/c=0.3, ω=10-100 Hz

9

• Damping Cavg for OR-SFD is 11% larger than Cavg for PR-SFD.
• Added mass Mavg ~30 kg as supply pressure decreases.
• Damping coefficients Cavg ↓ as lubricant supply pressure ↓.

c=373 µm, r/c=0.3, ω=10-100 Hz

OR-SFD & PR-SFD C and M vs. supply pressure

10

Peak film pressure vs. freq

Peak-peak dynamic pressure [bar] Frequency [Hz] r/c=0.3 Ps=0.7 bar Ps=3.5 bar Ps=6.2 bar

OR-SFD

Air ingestion

For Ps=0.7 bar, and whirl freq. > 60 Hz, peak-to-peak dynamic pressure  stops growing (due to air ingestion).

Peak-peak dynamic pressure [bar] Frequency [Hz] Ps=0.7 bar Ps=3.5 bar Ps=6.2 bar r/c=0.3 Air ingestion

PR-SFD

c=373 µm, r/c=0.3

11

PR-SFD pressure profiles

Pressure profiles for Ps=3.5 and 6.2 bar are almost identical. Spikes in pressure may be due to bursts of leakage thru PR slits.

r/c=0.3, ω= 90 Hz

Ps=0.7 bar Ps=2.1 bar Ps=3.5 bar Ps=6.2 bar

12

OR-SFD pressure profiles

r/c=0.3, ω= 90 Hz

Pressure profiles for Ps=3.5 and 6.2 bar are ~ identical. There are no sharp spikes on pressure.

Y X θ=0° θ=90° O-ring Discharge hole

(φ=2.0 mm)

P4(θ=225o) Measured point

Ps=0.7 bar Ps=2.1 bar Ps=3.5 bar Ps=6.2 bar

13

Sudden loss of flow

Tests conducted with SFD operating (under dynamic load) with amplitude r=0.2c. 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

Displacement, X (µm) Displacement, Y (µm)

Out of sensor range Clearance

Displacement, X (µm) Displacement, Y (µm)

Out of sensor range Clearance

Displacement, X (µm) Displacement, Y (µm)

Clearance

Y X θ=0° θ=90° O-ring Feedhole

(φ=2.3 mm)

Discharge hole

(φ=2.0 mm)

Y X θ=0° θ=90° Feedhole (θ=45o) PR slit (θ=135o)

OR-SFD PR-SFD

Ps=3.5 bar, Qs=2.4 LPM Ps=6.2 bar, Qs=3.0 LPM Ps=3.5 bar, Qs=3.5 LPM Ps=6.2 bar, Qs=6.0 LPM

Ps=Qs=0.0 at t >0

Jump & static

• ffset

15

0 sec 1 sec 2 sec 3 sec 4 sec 5 sec Recorded time

WATERFALLs of motion

Y X θ=0° θ=90° O-ring Feedhole

(φ=2.3 mm)

Discharge hole

(φ=2.0 mm)

Y X θ=0° θ=90° Feedhole (θ=45o) PR slit (θ=135o)

OR-SFD PR-SFD

Ps=Qs=0.0 at t >0

Ps=3.5 bar, Qs=2.4 LPM Ps=3.5 bar, Qs=4.5 LPM

Jump & static

• ffset

16

Conclusion

• Both O-ring and piston-ring sealed ends SFDs

show similar damping and added mass coefficients.

• For a large supply pressure (Ps) performance of a sealed ends

SFD does not change with an increase in squeeze film velocity (Vs=rω).

• 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 (?)