Introduction Tilting pad journal bearings (TPJB) support rotating - - PowerPoint PPT Presentation
May 2017 Year VI A CCOUNTING FOR T HERMALLY I NDUCED P AD D EFORMATIONS AND I MPROVING A F EEDING G ROOVE T HERMAL M IXING M ODEL TRC-B&C-01-17 Luis San Andrs Behzad Abdollahi Mast-Childs Professor Graduate research assistant A
Graduate research assistant
Mast-Childs Professor
TRC-B&C-01-17
A Computational Model for Tilting Pad Journal Bearings
Viscous shearing causes film temperature rise and power loss. High temperature in a pad
(Babbitt liner becomes soft ~121 °C).
Lubricant loses viscosity. Hot clearance ↓ and preload ↑ to affect the minimum film thickness, load capacity, & bearing force coefficients. x y
Shaft rotation speed, Ω Static load, W Bearing housing Pad Pivot Fluid film Lubricant in the groove Lubricant in the sump Orifice 2
Aim : reduce temperature rise & flow supplied with efficient lubricant delivery arrangements
Goal: To accurately predict bearing performance without costly & time extensive tests.
induced deformation of pads, shaft, and housing affecting bearing performance.
conventional model for thermal and flow mixing in a groove region.
3
2 2 2
1 1 T T r r r r r
4
𝝁 is an empirical coefficient
sup LE TE sup sup TE LE LE LE
(QTE) and downstream flow (QLE).
predicted (during design)
rarely varying with operating condition.
5
1 2 3 4
2 Sup
Q
3 Sup
Q
4 Sup
Q
4 TE
Q
1 LE
Q
W
1 Sup
Q
2 Sup
Q
3 Sup
Q
4 Sup
Q
Feed Groove
Plenum
1 Sup
Q
total Sup
Q
supply flow rate distributes evenly as Operation with journal eccentricity:
He, M., Cloud, C. H., Byrne, J. M., and Vazquez, J. A., 2012, 41st Turbomachinery Symposium He, M., Allaire, P., Barrett, L., and Nicholas, J., 2005, Trib. Trans. total sup i sup
Q Q n
1 4 1
( )
LE TE sup
Q Q Q
6
↓demand
downstream pad at its leading edge film. ↓demand
Introduce a groove demand parameter (Ci) to quantify the need of fresh flow from feed port:
1, , 1 | i shear i i n i i pressure TE
Q C Q Q
Flow at pad leading edge & trailing edge=
shear flow -/+ pressure flow
, /2 3 , /2 ,
2 12
| |
LE TE LE TE LE TE
shear pressure L s s L
Q Q Q R Lh h P dz R
7
Example : flow fraction (𝜷𝒋) for each feed groove vs. shaft speed & spec. load Total supply flow must meet total demand:
1 n total i i
C C
A fraction of total supply flow is allocated to each feed port:
; 1, ,
i total total i sup sup i sup total
C Q Q Q i n C
Novel Thermal Mixing Model: Flow Distribution
8
zero load (centered shaft).
require of lesser flow, while pad 3 receives most of the lubricant flow.
upstream pad (3) → low demand
4 pad bearing
Example : flow fraction (𝜷𝒋) for each feed groove vs. shaft speed & spec. load Total supply flow must meet total demand:
; 1, ,
i total total i sup sup i sup total
C Q Q Q i n C
Novel Thermal Mixing Model: Flow Distribution
9
zero load (centered shaft).
flow from upstream pad → low demand
flow fraction amongst pads becomes more uniform.
5 pad bearing
Novel Thermal Mixing Model: Flow balance at a port
is drawn from churning lubricant in a groove.
Nicholas, J. C., Elliott, G., Shoup, T. P., and Martin, E., 2008, 37th Turbomachinery Symposium Ha, H. C., Kim, H. J., and Kim, K. W., 1995, ASME J. Tribol.
Based on descriptions in:
1 1
if
i i i TE sup LE i i i i SL TE sup LE
Q Q Q Q Q Q Q
1 1
if
i i i TE sup LE i i i i gr LE TE sup
Q Q Q Q Q Q Q
a port as a side leakage flow.
ith pad
(downstream)
TE
Q
gr
Q
2
SL
Q
LE
Q
(i-1)th pad
upstream
Sup
Q
10
2
SL
Q
Thermal energy (heat) flows mainly by means of fluid motion,
advection heat transfer mechanism:
p
carry in thermal energy.
Conservation of energy for sub control volumes:
11
Side leakage stream (QSL, TSL) Groove churning stream (Qgr, Tgr)
Control volume analysis:
Tgr)
adjacent pad walls (ΦLE, ΦTE)
From conservation of energy, film temperature at downstream pad leading edge:
1 1 i i i i i i i TE LE TE TE sup sup SL SL gr gr p i LE i LE
12
13
Hagemann et al., 2013, GT2013-95004; Kukla et al., 2013, GT2013-95074.
axially shifted.
force coefficients.
14
Shaft rotational speed Ω [RPM] 500–3000 Shaft surface speed ΩR [m/s] 13–79 Specific Load W/(LD) [MPa] 1–2.5 Load orientation LBP Number of pads 5 Shaft diameter [mm] 500 Pad thickness [mm] 72.5 Bearing axial length [mm] 350 Pad arc length 56° Pivot offset 0.6 Preload 0.23 Pad clearance [μm] 300 Lubricant ISO VG32
Cp/R = 0.0012 L/D = 0.7 TEHD predictions include both thermally and pressure induced deformations
15
15 30 45 60 75
70 170 Angle (deg) Test data
1 2 3 4 5
Pad Surface Temperature Rise (°C) New model prediction Conventional model prediction, λ = 0.9 Cgr = 0.2
N = 3000 RPM W/(LD) = 2.5 MPa
New model improves
model predictions (up to 17 °C). Conventional model predicts supply flow rate 70% larger than actual.
lubricant leaving each pad (side or axially) is not immediately forced out.
1 & 5 is drawn from the captured oil inside the bearing housing.
16
15 30 45 60 75
70 170 Angle (deg) Test data, Q=420 L/min
1 2 3 4 5
Pad Surface Temperature Rise (°C) Prediction, Q=420 L/min Test data, Q=210 L/min Prediction, Q=210 L/min Cgr = 0.2
N = 3000 RPM W/(LD) = 1 MPa
End-seal C/R=0.004
17
Cut supply flow in half → ~ 20 °C temperature raise.
for operation with reduced flow.
20 40 60 80 100
70 170 Angle (deg)
1500 RPM New model, Q=420 L/min Simple model 3000 RPM 4500 RPM
1 2 3 4 5
Cgr = 0.2
W/(LD) = 1 MPa Increase shaft speed by 1500 RPM → ~ 20 °C temperature raise. 4500 RPM → Likely pad flow starvation. Conventional model predicts flow!
Pad Surface Temperature Rise (°C) 18
End-seal C/R=0.004
Coghlan, D. M., and Childs, D. W., 2015, GT2015-42331. Coghlan, D. M., 2014, M.S. Thesis, Texas A&M University.
» Flooded single-orifice (SO), labyrinth end seals » Evacuated leading edge groove (LEG) » Evacuated spray-bar (SB) » Evacuated spray-bar blocker (SBB)
19
Shaft rotational speed Ω [RPM] 7000-16000 Shaft surface speed ΩR [m/s] 38-85 Specific Load W/(LD) [MPa] 0.7-2.9 Load orientation LBP Number of pads 4 Shaft diameter [mm] 101.59 Pad thickness [mm] 190 Bearing axial length [mm] 61 Pad arc length 72° Pivot offset 0.5 Preload 0.3 Pad clearance [μm] 134 Lubricant ISO VG46 Total supply flow (fixed) [LPM] 42 –38
Cp/R = 0.0013 L/D = 0.6
0° 1 2 3 4 θ x W y
Flooded housing
20
Evacuated housing
10 20 30 40 50 60 70 80 100 200 300 Angle (deg)
Supply Temp. 2.9 MPa 0.7 MPa 2.1 MPa Test Data Predictions 1 2 3 4
N=7000 RPM
Cgr = 0.6 Qtotal=42 L/min
bearing directly without ever lubricating pads.
test delivered (42 LPM).
Pad Surface Temperature Rise(°C)
0° 1 2 3 4 θ x W y
21
22 10 20 30 40 50 60 70 80 100 200 300 Angle (deg)
Supply Temp. 2.9 MPa 0.7 MPa 2.1 MPa Test Data Predictions
Cgr = 0.6 Qtotal=42 L/min
N=16000 RPM
Pad Surface Temperature Rise(°C)
LPM delivered Likely oil starvation on pad 4 (unloaded)
model Qsup=0.
0° 1 2 3 4 θ x W y
There is no recirculation flow (Qgr) in an evacuated housing TPJB.
10 20 30 40 50 60 70 80 100 200 300 Angle (deg) LEG SBB Test Data
0° 1 2 3 4 θ x W y
1 2 3 4
N=16000 RPM Q=42 L/min SO Cgr=0.9 Cgr=0.5 Cgr=0.2 Q=38 L/min
Pad Surface Temperature Rise(°C)
Model predicts pad temperature with less than 10 °C difference than test data.
23
SO
(single orifice)
SB
(spray bar)
SBB
(spray bar blocker)
LEG
(leading edge groove) Graphics taken from Coghlan, D. M., 2014, M.S. Thesis, Texas A&M University.
Oil feed type influences film temperature due to various factors.
thermal mixing model, the predicted flow rate must be same as actual supplied flow.
temperature prediction by up to 17 °C (37 °C at reduced supply flow).
port) have significant influence on the lubricant film temperature.
efficiency parameter (Cgr) does not need tailoring to each
24
25
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Single Orifice Spray Bar Spray Bar Blocker Leading Edge Groove Evacuated (w/o end seals) Flooded (w/ end seals)
SBB) reduce hot oil carry over → side leakage of lubricant carries most of thermal energy form hot upstream oil → Cgr 1 (TSL TTE : exit temperature of upstream pad).
groove → Cgr 0 (Tgr TTE).
26
Rasool Koosha
Graduate research assistant
Mast-Childs Chair Professor TRC-B&C-05-17
To develop a thermohydrodynamic (THD) predictive tool for thrust bearings.
Pressure generation
pivot deformations Axial force coefficients (K,C)
3D fluid film temperature
3D pad temperature
deformations (not yet included) 28
29
temperature distribution in fluid film and pads.
and turbulence flow.
model in a feed port.
to applied load and frequency reduced axial stiffness and damping.
Almqvest et al. (1999) Glavatskih (2002)
OD 228 mm ISO VG46 oil 30-40-60 ˚C supply T measured power loss. 0.5-2.0 MPa applied load 1500-3000 rpm
Almqvist, T., et al., 1999, J. Tribol.; Glavatskih. S. B., 2002, J. Tribol.
Measurement accuracy Pad sub-surface temperature ±1 K Fluid film pressure ±4 % Fluid film thickness ±1.5 µm Power loss ±1 %
30
1.5 MPa specific load 1.8 kRPM rotor speed 50 ˚C oil supply temperature 31 Pressure transducers Pc 25 and Pc 75 (Pad 4)
TEST DATA: Almqvist, T., et al., 1999, J. Tribol.; Glavatskih. S. B., 2002, J. Tribol.
symmetric
moves towards pad’s trailing edge as the applied load increases.
pressure differ at most by 8%.
32 40 ˚C oil supply temperature Thermocouple Tp3 75/75 (Pad 3)
TEST DATA: Almqvist, T., et al., 1999, J. Tribol.; Glavatskih. S. B., 2002, J. Tribol.
corner of pad trailing edge / outer diameter.
with an increase in applied load and/or rotor speed.
and prediction (max 17%) increases with load and rotor speed.
33 40 ˚C oil supply temperature Displacement sensor (Pad 5)
TEST DATA: Almqvist, T., et al., 1999, J. Tribol.; Glavatskih. S. B., 2002, J. Tribol.
thickness increases as applied load increases or rotor speed decreases
rotor speed increases.
prediction (max 20%)
34
3 krpm rotor speed
Power loss increases with speed and load. Increase in oil supply temperature increases power loss. Difference test and prediction max 8% at 3krpm and 2.0 MPa.
Objective: Produce up-to-date predictive computational tool for the analysis of TPTB performance. Tasks:
(a) Account for pads’ elastic deformations due to pressure and
temperature deliver a thermoelastohydrodynamic (TEHD) model. (b) Include thrust collar tilts to quantify TB reaction moments and moment/tilt coefficients. (c) Upgrade Graphical User Interface for XLTRC2
35
Budget
Support for graduate student (20 h/week) × $2,400 ×12 months $ 28,800 Fringe benefits (2.5%) and medical insurance $ 4,995 Travel to (US) technical conference $ 1,200 Tuition & allowable fees $ 9,600 Total Cost:
$44,595