1. ASME Turbo Expo 2012 June 11-15, 2012, Copenhagen, Denmark
On the Effect of Thermal Energy Transport to the Performance of (Semi) Floating Ring Bearing Systems for Automotive Turbochargers
Luis San Andrés
Mast-Childs Professor, Fellow ASME
Texas A&M University GT
Accepted for journal publication

2. Authors GT2012-68355 Luis San Andrés Vince Barbarie
Thermal Energy Transport to the Performance of (Semi) Floating Ring Bearing Systems for Automotive Turbochargers
Authors
Luis San Andrés
Turbomachinery Laboratory
Texas A&M University
Vince Barbarie
Avijit Bhattacharya
Kostandin Gjika
Honeywell Turbo Technologies
Torrance, CA 90504
Honeywell Turbo Technologies,
Thaon-les-Vosges, France
Supported by Honeywell Turbocharger Technologies (HTT) 2

3. Fully Floating Bearing
Types of bearing supports
Ball Bearing
Semi Floating Bearing
Fully Floating Bearing
Low shaft motion, expensive, limited lifespan
Oil lubricated bearings are economic with longer life span; but prone to harmful subsynchronous whirl & depend on engine oil condition.
The driver:
Increased IC engine performance & efficiency demands of robust turbocharging solutions

4. Thermal management & reduce thermal loading
Major challenges
extreme operating conditions:
- Low Oil Viscosity, e.g. 0W30 or 0W20
- High Oil Temperature (up to 150°C)
- Low HTHS (2.9); Low Oil Pressure (1 bar),
- Increased Max. Turbocharger Speed 5 kHZ
- Variable Geometry Turbo Technology & Assisted e-power start up
- High Engine Vibration Level
- More Stringent Noise Requirements
Thermal management & reduce thermal loading
Need predictive too to reduce costly engine test stand qualification

5. Literature Review: TAMU work
2004
IMEchE J. Eng. Tribology
2005
ASME J. Vibrations and Acoustics
ASME DETC 2003/VIB-48418
ASME DETC 2003/VIB-48419
2007
ASME J. Eng. Gas Turbines Power ASME GT
ASME J. Eng. Gas Turbines Power ASME GT
ASME J. Tribology
IJTC
ASME DETC
2010
ASME J. Eng. Gas Turbines Power ASME GT
IFToMM Korea
TC linear and nonlinear rotordynamic codes – GUI based – including engine induced excitations
Realistic bearing models: thermohydrodynamic
Novel methods to estimate imbalance distribution and shaft temperatures
NL analysis for frequency jumps (internal & combined resonances) and noise reduction
Measured ring speeds with fiber optic sensors
Predictive tool for shaft motion benchmarked by test data

6. VIRTUAL TOOL for TC NL shaft motions
Tool demonstrated 70% cycle time reduction in the development of new CV TCs. Since 2006, code aids to develop PV TCs with savings up to $1XX k/year in qualification test time
Predicted shaft motion
Measured shaft motion
ASME DETC
TC testing is expensive and time consuming
Predictive tool saves time and resources

7. Conjugate heat transfer in TCs
Thermal energy analysis in TCs complicated b/c of
Hot gas -work and heat flow from turbine
Cold gas +work and heat flow from the compressor
internal heat flow across shaft from T to C and radially thru bearings
Mechanical drag power in bearings
Heat flow to/from casing to ambient (convective and radiant)
Engine lubricated bearings: (a) low friction-load support (b) oil carries away heat (cooling)

8. Heat flows & energy transfer in a TC
Hot air (energy) in
Compressed hot air (energy) out
Oil in
-Hot air (energy) out
Cold air (energy) in
turbine
work
compressor
Heat conducted (shaft)
Heat conducted (casing)
Heat conducted (casing)
Bearing drag power generation
Heat conducted (casing)
Oil out
Baines, N., Wygnant, K., Dris, A., 2010, J Eng Gas Turb. Power,

9. Thermal energy analyses in TCs use
Lumped parameter models with empirical formulas for heat transfer coefficients and simplified formulas for drag power, flow & heat flow in the lubricated bearings
Current 3D modeling stresses on solids with over-simplified coupling to the lubricant flows
GOAL
Engineered thermal management to avoid severe thermal loading with improved reliability of bearing system:
avoid oil coking, optimize flow rates, ensure proper clearances, eliminate seizure.

10. SFRB system in engine-oil lubricated TC
Lubricant flow paths into bearings on turbine and compressor sides
casing
Oil supply at Psup, Tsup
compressor
turbine
shaft
Turbine side bearing
Outer film with ½ moon groove
Compressor side bearing oil supply holes
to inner and outer films
Oil supply holes to inner film
Semi-floating
ring bearing
Oil discharges at ambient pressure Pa
Anti-rotation pin

11. Geometry & coordinate system for typical SFRB
Definitions:
X,Y: fixed (inertial) coordinate system
g : direction of gravity
q :Circumferential coordinate Y Y
Oil supply hole LG
½ moon groove
outer film
Casing
Z : axial coordinate
Lo : axial length of outer film
Li : axial length of outer film
LG: axial length of ½ moon groove
DRo: Ring outer diameter
DRi: Ring inner diameter
DJ: Shaft (journal) diameter
DB: Bearing casing inner diameter
DB-DRo : outer film diametral clearance
DRo-DJ : inner film diametral clearance
inner film q 0º Li Z DJ
DRi X
Shaft
shaft
Shaft rotation W WR
Ring Lo g
Ring rotation
DRo DB

12. Kinematics of journal and ring
Nomenclature:
W : journal rotational speed
WR: ring rotational speed
q :Circumferential (angular) coordinate Y = e eR eJ +
co : radial clearance outer film
ci : radial clearance inner film
ho: outer film thickness
hi : inner film thickness
eRX, eRY: Ring center eccentricity components
eX, eY: Shaft (journal) center eccentricity components
eJX, eJY : Eccentricity of journal relative to ring
ring rotation WR
Journal rotation q W e OR eJ X eR
journal
ring
Outer film thickness
Inner film thickness

13. Axial view of inner and outer films: nomenclature
Oil inlet,
Psup, Tsup
Inlet
½ moon
groove
Ring,
TR(r)
Outer film,
To(q,z) TC Rc z
Po,To
Shaft, TS
TRo Ro
TRM WR Ri
TRi W
Pi,Ti
Inner film,
Ti(q,z) RM TS
PA, ambient
pressure z PA
Casing, TC Rs
Feed
hole

14. Hydrodynamic pressure generation
Nomenclature
P : film pressure
h : film thickness
m : viscosity, fn (T)
TRM
Ring
Pi,Ti
Po,To TS
Casing TC
shaft
Outer
film
Inner
film
W journal rotational speed
WR ring rotational speed
Q circumferential coordinate
Z axial coordinate
RJ: Shaft (journal) radius
RB: Bearing casing inner diameter
Major assumptions:
Laminar flow without fluid inertia effects
Average viscosity across film thickness
Reynolds equations for inner & outer films

15. Heat flows & power in a FRB
casing
Heat flow into casing TC
Heat flow
carried
by oil
Flow outer To
Outer film
Mechanical drag power
TRo
Heat flow into ring
Ring
TRi
Flow inner
Inner film Ti
Heat flow from shaft
shaft TS
Mechanical drag power W

16. Thermal energy transport in inner film
TRM
Pi,Ti
Po,To TS
Casing TC
shaft
Nomenclature
Ti: inner film temperature
TJ, TRi : shaft (journal) and ring ID temperatures
hJ, hRi : heat convection coefficients
Inner film mechanical energy dissipation:
with circ. and axial mass flow rates:

17. Thermal energy transport in outer film
TRM
Pi,Ti
Po,To TS
Casing TC
shaft
Nomenclature
To: outer film temperature
TB, TRo : bearing casing and ring OD temperatures
hB, hRo : heat convection coefficients
Outer film mechanical energy dissipation:
with circ. and axial mass flow rates:

18. Heat conduction in semi-floating ring
Nomenclature
TR: ring temperature
TJ, TRi : shaft (journal) and ring ID temperatures
hJ, hRi : heat convection coefficients
kR: ring material conductivity
qR : heat flow
Major assumptions:
Steady state, no heat flow in axial direction,
No effect of ring rotation r Q

19. Heat conduction in semi-floating ring
TRM
Ring
Pi,Ti
Po,To TS
Casing TC
shaft
Major simplification
Radial heat conduction only r Q
Nomenclature
TR: ring temperature
QR: radial heat flow
kR: ring material conductivity

20. Heat convection Models
Heat flow: Q = h A (TS – Ti)
A: wetted area for heat transfer Ts
h: heat convection coefficient, a function of Nusselt #, oil conductivity and hydraulic diameter (=clearance).
Nusselt # =depends on flow conditions (Prandtl # and Reynolds #) 1
Reynolds/Colburn Analogy), Nu=3 Pr0.33 2
Kays and Crawford - constant wall temperature, Nu =7.54 3
Kays and Crawford - constant wall heat flux, Nu =8.22 4
Haussen - thermally developing constant wall temperature, Nu >3.657 5
Shah thermally developing constant wall heat flux, Nu > 4.364 6
Stephan - Simultaneous developing, constant wall temp, Nu >3.66 7
Stephan - Simultaneous developing constant wall heat flux, Nu > 4.364

21. Numerical method of solution
Finite element method for Reynolds Eqns.
b) Control volume method for energy transport Eqns.
Includes balance of drag torques, material properties f(T), bearing clearance changes due to temperature rise, etc.

22. Example Semi FRB for PV turbine bearing
120C
213C
Shaft (journal)
RING
CASING
Oil inlet
Oil: SAE 5W-30
Bearing dimensions
Inner Film
Outer film
Diameter
7.9
14.1 mm
length
4.6
6.2
Cold clearance
7.5 35 m 22

23. Meshes for inner and outer flow domainsX
=132 Y Z
Casing
½ moon groove
Feed hole x 4
groove
journal
ring
Mesh: outer film
NEX=45, NEY=12 z
½ moon groove
Circ. groove
132o
Mesh: inner film
NEX=52, NEY=12 q z
Oil supply hole
(4x)
Axial groove
(4 x)
Engineered design to improve flow delivery and reduce temperature rise 23

24. Predictions for inner film at
240 krpm
(a) Pressure field (bar) q z
TS=213C
Feed hole & axial groove
Tsup=120C z q
(b) Temperature field (C)
Oil heats quickly along axial plane

25. Temperatures: maximum in films
Inner film temperature
shaft T (< flash T).
Outer film relatively cold.
Shaft Temp
inner film
exit mixed films
outer film

26. Temperatures: average in films
Shaft Temp
Inner film much hotter than outer film. Exit mixing lubricant temperature nearly constant > 90 krpm
inner film
exit mixed films
outer film

27. Ring Temperatures: ID, OD and mean
Shaft Temp
Large radial temperature gradient across ring.
OD-ID Temperature difference ~ 40oC.
RING material conductivity is important.
RingID
RingOD
(mean radius)

28. Oil viscosity (average): inner & outer films
Relative to supply:
Inner film viscosity decreases because of increase in film temperature (> Tsup)
outer film
inner film
Thermal effects can not be ignored

29. Oil flow rates: inner & outer
Oil flow is minimum at top speed.
Outer/inner flow decreases/increases because of clearance shrinks/grows + lower oil viscosity
outer film
Flow=1
= out+in
inner film

30. Heat flows and drag power
Low speeds: heat from shaft dominates.
High speeds: drag power losses increase. For all conditions lubricant carries more energy that casing soaks.
Heat from shaft
Heat to lubricant
Drag power
(inner film)
Heat to ring
Heat to casing + =1 =

31. low speed (45 krpm) Thermal energy transport and balance 36 % 27 % 97%
Width of boxes denotes intensity of heat flows
100%
36 %
27 %
Heat from shaft
97%
Heat to ring
Heat to casing
Heat to fluid (i+o)
Heat to fluid (o)
10 %
Heat
to fluid (i)
74 %
64 % 3%
Drag Power
(inner & outer)
Mechanical shear flow energy heating gas film is advected by gas film flow (axial removal) and also conducted into shaft and top foil back surface.
Heat conducted into shaft is removed by inner flow stream.
Heat flowing from the back of the top foil is removed by either forced outer cooling stream or conducted into bearing cartridge for natural convection.
Note significant amount of mechanical energy that converts into expansion (-) work
Without forced cooling flows, ~ 58 % of the total
energy is carried away by the gas film flow leaving the
bearing through its axial edges plus 12 % convected
naturally at the back of the top foil. The amount of heat
conducted into the bearing cartridge and shaft adds to 31 %.
On the other hand, with an outer cooling flow stream, there
is only 11.2% of heat advected by the gas film since it
operates at a much lower temperature; while ~81.9% of the
energy is dumped into the outer cooling stream. The addition
of the inner flow stream aids to further cooling the bearing;
albeit it is not as efficient as the outer stream to remove heat,
as shown in Fig. 5 (c). With an outer cooling stream, the heat
conducted into the bearing housing amounts to just 1.2% to
1.5% of the available energy.
Lubricant carries away heat from shaft mainly.
low speed (45 krpm)

32. high speed (240 krpm) Thermal energy transport and balance 24 % 17 %
Width of boxes denotes intensity of heat flows
100%
24 %
17 %
Heat from shaft
65%
Heat to ring
Heat to casing
Heat to fluid (i+o)
Heat to fluid (o)
8 %
Heat
to fluid (i)
35%
83 %
76 %
Drag Power
(inner & outer)
Mechanical shear flow energy heating gas film is advected by gas film flow (axial removal) and also conducted into shaft and top foil back surface.
Heat conducted into shaft is removed by inner flow stream.
Heat flowing from the back of the top foil is removed by either forced outer cooling stream or conducted into bearing cartridge for natural convection.
Note significant amount of mechanical energy that converts into expansion (-) work
Without forced cooling flows, ~ 58 % of the total
energy is carried away by the gas film flow leaving the
bearing through its axial edges plus 12 % convected
naturally at the back of the top foil. The amount of heat
conducted into the bearing cartridge and shaft adds to 31 %.
On the other hand, with an outer cooling flow stream, there
is only 11.2% of heat advected by the gas film since it
operates at a much lower temperature; while ~81.9% of the
energy is dumped into the outer cooling stream. The addition
of the inner flow stream aids to further cooling the bearing;
albeit it is not as efficient as the outer stream to remove heat,
as shown in Fig. 5 (c). With an outer cooling stream, the heat
conducted into the bearing housing amounts to just 1.2% to
1.5% of the available energy.
Drag power losses increase. Lubricant carries away largest portion of heat flow.
high speed (240 krpm)

33. Drag power and heat from shaft
High heat flow
High power
Inlet plane
low power
240 krpm
240 krpm
Low heat flow
Exit plane
Exit plane
30 krpm
30 krpm
Heat from shaft (W)
Drag power (W)
Drag power and heat from shaft are large at inlet because of inlet (cold) lubricant.

34. Conclusions
Heat flow from hot shaft into inner film is large; more so at the inlet plane where oil is cold;
The inner film temperature increases quickly (viscosity drops) due large heat flow from shaft and drag shear power;
The floating ring has a large radial temperature gradient;
At all rotor speeds, the lubricant flows carry more than 70 % of the total energy input. The rest soaks into the TC casing. The bearing design must allow for adequate flow paths to cool components.
Tool integrated into sponsor engineering design practice to predict thermal loading and mechanical stresses and to ensure lubricant does not overheat (coking)

35. Questions (?) Acknowledgments
Thanks to Honeywell Turbocharging Technologies ( )
Questions (?)
Learn more at:
Copyright© 2012 Luis San Andres