Interim May Report 2019 TRC-B&C-02-19 MEASUREMENTS TO QUANTIFY THE EFFECT OF A REDUCED FLOW RATE ON TILTING PAD JOURNAL BEARING PERFORMANCE – STATIC AND DYNAMIC Dr. Luis San Andrés Jon Toner Graduate Research Assistant Mast-Childs Chair Professor 1 TEES Project # 28-258124-00135
TRC interest Reduction in flow rate reduction in drag power loss and more efficiency, though with increased pad temperatures & drop in damping. Savings in pumping and lubricant storage make the case for low flow… how low is a low flow rate enough to maintain reliability Too low (and energy efficient) TPJB operation ? 2
Objective and tasks • To quantify the effects of lubricant flowrate on tilting pad bearing performance: • Drag power & load capacity • Pad metal temperatures • Force coefficients (K, C, M) Prior art [1] Decamillo, S., Brockwell, K., 2001 “A Study of Parameters That Affect Pivoted Shoe Journal Bearing Performance in High- Speed Turbomachinery”, Proc. TPS, Texas A&M. [2] Dmochowski, W. M., Blair, B., 2006, “Effect of Oil Evacuation on the Static and Dynamic Properties of Tilting Pad Journal Bearings”, Trib. Trans . , 49. [ 3] Nichols, B., 2017, “ Experimental Measurements and Modeling of Tilting-Pad Bearing Performance and System Stability Under Reduced Oil Supply Flow Rates” , Thesis, UVA .
Test Rig Legacy of D. Childs & students 4
Test Rig Features Test-Rig Capabilities Strain gage torquemeter & Max. rotor speed 16 kRPM coupling directly measures Max. applied static load 20 kN drag torque. Max. measurable torque 100 Nm Floating bearing on rigid Max. supply oil flow rate ~20 GPM rotor. 3.5”, 4”, 4.5” Available shaft OD sizes 3.5” Max. bearing length 5
Test Rig Load Devices Pneumatic Cylinder Hydraulic Actuator • Pneumatic cylinder applies static load. • Pair of hydraulic actuators deliver dynamic loads via stingers. 6
Test Bearing TL bearing tested by Coghlan (D. Childs team) in 2015-ff 7
Test bearing – load between pads Thermocouples in pad and in oil supply outer annulus Applied 2,135, 6,405, Load, W 12,810 N L/D 0.6 Specific 345, 1,034, 2,068 Shaft diameter 4.0 in (101 mm) Load, W/(LD) kPa 303 psi 2.4 in (61 mm) Length B radial cold clearance 4.52 mil (0.115 mm) ISO VG46 oil at 60C hot clearance (6 & 12 krpm) 4.20 mil (0.106 mm) 16.4 cPoise & 837 kg/m 3 0.3 Design pad preload Spherical Pivot Offset 0.5 Pad Arc Length ( ° ) 72 ° AISI 1018 Pad Thickness 0.75 in Babbitted pad surface Lubrication condition Single Orifice b/w pads, Flooded (with end 8 seals)
Oil supplied flow rate - theory flow rate ~ shaft speed VARY Flow from 150% 100% (nominal) 20% or Q = N p ½ ( ½ W D ) L C r (1- l ) less (if safe) N p = number of pads 50 6 12 Flow rate (LPM) Ω = shaft speed (rad/s) 40 Nominal D = shaft diameter (m) 150% (100%) 30 L = bearing axial length (m) C r = bearing radial clearance (m) 20 l = hot-oil carry over coefficient. 10 50% 0 0 4 8 12 16 Tests at two shaft speeds Low rotor speed (krpm) High 1. 6 krpm (32 m/s) Shaft speed (rpm) * ~14. 4 LPM 2. 12 krpm (64 m/s surface speed) ~28.8 4 LPM 9
Test Results Load between pads (LBP) 2 shaft speeds x 3 static loads Shaft speed 6 and 12 krpm Specific Load, 345, 1,034, 2,068 W/(LD) kPa 10
Journal locus vs. speed vs. flow 6 kRPM 12 kRPM L o a d e Y Eccentricity is nearly parallel to load direction and increases with load and is much smaller as shaft speed doubles. e X L Journal eccentricity increases slightly as o a flow rate decreases small impact on d film thickness. ISO VG46 inlet T = 60C 11
Shaft eccentricity vs. flow vs. load 6 kRPM 12 kRPM L o a d Flow (LPM) Flow (LPM) Y Eccentricity decreases with shaft speed and increases with load. e Journal eccentricity increases slightly as X L flow rate decreases . (semi-log scale). o a d Low flow does not produce a too small film thickness. 12
M aximum ( Loaded ) pad temperature rise L o a d 12 kRPM 6 kRPM Flow (LPM) Flow (LPM) A very low flow (50% & below) does produce large increase in pad peak temperature. Load and shaft speed have minor effect. Inflection in temperature vs flow due to uneven thermal field in supply annulus ( more later ). ISO VG46 inlet T = 60C 13
M aximum (un loaded ) p ad t emperature rise 6 kRPM 12 kRPM Flow (LPM) Flow (LPM) A low flow (50% or less of nominal) produces a quick temperature rise. Load and shaft speed have negligible effect. Larger than 100% flow rate produces no changes. ISO VG46 inlet T = 60C 14
Oil exit t emperature rise vs. flow vs. speed 6 kRPM 12 kRPM Flow (LPM) Flow (LPM) Shaft speed has an effect on exit oil temperature; more so than load. Low flow rates produce a significant oil exit temperature rise. Alarming only for very low flows (20% nominal or less). ISO VG46 inlet T = 60C 15
Drag torque vs. flow vs. speed 12 kRPM 6 kRPM L o a d Flow (LPM) Flow (LPM) Drag torque drops quickly as flow rate decreases. Twice shaft speed ~ 2 x drag torque. 16
Drag power vs. flow vs. speed Power = Torque x shaft speed L o a d 12 kRPM 6 kRPM Flow (LPM) Flow (LPM) Drag power drops quickly as flow rate decreases. Savings of 50% or more in drag power with low flow rate (40% or lower). Overflow (> 100%) increases power consumption (~20%) for operation at 12 krpm (64 m/s). ISO VG46 inlet T = 60C 17
Force Coefficients Load between pads (LBP) 2 shaft speeds x 3 static loads Shaft speed 6 and 12 krpm Specific Load, 345, 1,034, 2,068 kPa W/(LD) 18
Procedure for force coefficients identification Step 1: Apply loads and measure bearing motions Apply forces with shakers pseudo-random frequency Y Y 1 0 F e 1 i t 2 i t X F Re F Re e X 2 X F 0 Y CCW CCW X force Y force ω is a set of frequencies =( 1, 2, 3,…, 17) x 9.77 Hz. Record bearing displacement z and acceleration a 1 2 1 2 x x X X (t) (t) 1 i t 1 2 i t z a z e e 2 a 1 2 1 2 y y Y Y (t) (t) EOM: Frequency domain Find parameters: 2 2 [ K i C M z ] F M a H K M C i S 19
Procedure for force coefficients identification Step 2: Estimate dry structure parameters NO lubricant 2 2 [ K M C z ] F i H K M C i S S S S S S S Step 3 : Bearing force coefficients = Lubricated system – Dry system (K, C, M) bearing = (K, C,M) L – (K, C, M) S Test system Dry Bearing (Lubricated) structure Y L O A D X 20
Y - Load Direct stiffness vs. flow rate direction 12 kRPM 6 kRPM L o a d Flow (LPM) Flow (LPM) Direct stiffness K YY is a Y function of load more than shaft speed or even flow rate. L o a X d ISO VG46 inlet T = 60C 21
Y - Load Direct damping vs. flow rate direction 12 kRPM 6 kRPM L o a d Flow (LPM) Flow (LPM) Direct damping C YY decreases as Y flow rate decreases ( all pads starve ). Significant drop for lowest load (345 L kPa [50 psi]) o a Advent of SSV? X d 22
SSV Subsynchronus vibrations 6.5 kRPM, 345 kPa (50 psi) load, 0.36 LPM (4%) 100% flow ~ 14.4 LPM 1X (108 Hz) SSV Low frequency spectrum (SSV hash) Y recorded for operation with berry-berry low flow rates (and small load). L o SSV “breathed in” and need to be excited. X a d 23
Complete Set of Force Coefficients (X & Y) …. upcoming 24
Other issues 25
Inlet Oil Supply Temperature Thermocouples affixed to bearing OD facing feed annulus near inlet orifices. Gravity Inlet Port 26
Temperatures in Oil Supply Annulus For very low oil flow rates supplied Temperatures around annulus not uniform & unsteady (likely not wetted surface). Difficult to control flow & oil inlet temperature (set 140F). 250 F 6kRPM, 2068 kPa (300 psi) load Temperature ( ° F) 200 F C 2.1 LPM 2.6 LPM A B 3.6 LPM 150 F set inlet T = 2.6 LPM 3.2 LPM 60C= 140F 120 F D Time span = 17 min 27
Results of Low Flow Limit Tests Low flow limit found by reducing oil flowrate at a constant rotor speed and specific load until: • 1) Pad Temperature exceeds 121C (250F) or • 2 ) SSV vibration appears • 3) Inlet temperature below target 60 ° C and/or annulus temperatures not uniform Cannot maintain control flowrate and/or oil inlet temperature) Limit of Low Oil Supply Load Flow Limit 345 kPa 2% (0.36 LPM) 3 6 kRPM (32 m/s) 1034 kPa 10% (1.4 LPM) 3 Flow=14.4 LPM 1 2068 kPa 5% (1 LPM) 345 kPa 15% (4.3 LPM) SSV 12 kRPM (64 m/s) 1 1034 kPa 15% (4.3 LPM) Flow=28.8 LPM 2068 kPa 23% (6.8 LPM) 1 28
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