Presentation at ASME/BATH 2015 Symposium on Fluid Power & Motion Control, Chicago, 12 October, 2015 by FPRL - Politecnico di Torino

1. POLITECNICO DI TORINO - Italy
Giorgio Altare – Massimo Rundo
ASME/BATH 2015 Symposium on Fluid Power & Motion Control
Chicago, October 12, 2015
CFD Analysis of Gerotor Lubricating
Pumps at High Speed:
Geometric Features Influencing the
Filling Capability

2. Politecnico di Torino
Dipartimento Energia
Fluid Power Research Laboratory
http://www.fprl.polito.it
Summary
• Model of the reference gerotor pump
• Experimental validation
• Simplified reference model
• Influence of geometric parameters on filling:
• Inlet pipe direction
• Profile of the suction port
• Height and diameter of the gears
• Number of chambers
2 / 17

3. Politecnico di Torino
Dipartimento Energia
Fluid Power Research Laboratory
http://www.fprl.polito.it
Reference unit: gerotor lube pump
Outlet port
Inlet port
Displacement = 19.8 cc/rev
Diameter of the outer gear = 62.1 mm
Gears thickness = 25 mm
Delivery volume
Double feeding
Recess for
axial balance
Valve spool
(blocked)
shaft
3 / 17

4. Politecnico di Torino
Dipartimento Energia
Fluid Power Research Laboratory
http://www.fprl.polito.it
inlet volume
tank
portion
pipe
variable
chambers
delivery volume
atmospheric pressure
blind port
CFD model (PumpLinx)
About 600 000 cells
outlet pressure
axial leakage (3 layers)
radial leakage (3 layers)
Equilibrium Dissolved Gas Model
4 / 17
Tip clearance
Tooth of
the inner
gear

5. Politecnico di Torino
Dipartimento Energia
Fluid Power Research Laboratory
http://www.fprl.polito.it
Test rig at FPRL
P1
P2
P1, P2: miniature pressure transducers on the pump
5 / 17

6. Politecnico di Torino
Dipartimento Energia
Fluid Power Research Laboratory
http://www.fprl.polito.it
Tests as function of speed (open circuit)
Constant delivery pressure (4 bar)
Constant temperature (40 °C)
Max error 7%
Theoretical
Config. R1 R2
1 no no
2 yes no
3 yes yes
R2
R1
Good evaluation of the limit speed
6 / 17

7. Politecnico di Torino
Dipartimento Energia
Fluid Power Research Laboratory
http://www.fprl.polito.it
and as function of inlet pressure (closed circuit)
Constant delivery pressure (4 bar)
Constant temperature (40 °C)
P1
0.06 bar
7 / 17
2%

8. Politecnico di Torino
Dipartimento Energia
Fluid Power Research Laboratory
http://www.fprl.polito.it
Reference simplified model
• Same rotors used for model validation
• Simplified geometry of the suction side
• Rotors fed from one side only
• Ideal timing
• Leakages only between the gears
Operating conditions
• Speed = 5000 rpm
• Delivery pressure = 4 bar
• Temperature = 40 °C
Flow rate = 50.34 L/min
Volumetric
efficiency = 50.8%
(square cross section,
radial position)
8 / 17

9. Politecnico di Torino
Dipartimento Energia
Fluid Power Research Laboratory
http://www.fprl.polito.it
Influence of inlet direction

0° : Tangential
cocurrent
direction of rotation
180° : Tangential
countercurrent
inlet volume
90°:axial
Max improvement
(from 51% to 59%)
with axial inlet
radial
axial
9 / 17

10. Politecnico di Torino
Dipartimento Energia
Fluid Power Research Laboratory
http://www.fprl.polito.it
Comparison of axial velocity fields
 = 90°  = 180°
Direction
of rotation
Lower
contraction
coefficient
10 / 17
15 m/s
0 m/s
Analyzed chamber

11. Politecnico di Torino
Dipartimento Energia
Fluid Power Research Laboratory
http://www.fprl.polito.it
Influence of inlet port profile

 = 0°  Ideal timing
 > 0°  Closing delay
Radial inlet pipe
Flow area
of a chamber
Volumetric efficiency
11 / 17

12. Politecnico di Torino
Dipartimento Energia
Fluid Power Research Laboratory
http://www.fprl.polito.it
Influence of pump displacement
Ref. V1 V2
Thickness (mm) 25 16.67 12.5
Displacement (cc/rev) 19.8 13.2 9.9
Speed (rpm) 5000 7500 10000
Same theoretical
flow rate (99 L/min)
12 / 17

13. Politecnico di Torino
Dipartimento Energia
Fluid Power Research Laboratory
http://www.fprl.polito.it
H12.5mm
H25mm
10 000 rpm 5 000 rpm
Axial velocity fields
Low axial velocity regions
13 / 17

14. Politecnico di Torino
Dipartimento Energia
Fluid Power Research Laboratory
http://www.fprl.polito.it
Influence of external diameter (D)
• Same thickness (H)
• Same displacement
• Ideal timing
• Different eccentricity (e)
The chamber flow area is always larger with
higher external diameters  better filling
14 / 17
Greater frontal surface

15. Politecnico di Torino
Dipartimento Energia
Fluid Power Research Laboratory
http://www.fprl.polito.it
Influence of axial thickness (H)
• Same diameter (D)
• Same displacement
• Ideal timing
• Different eccentricity (e)
15 / 17

16. Politecnico di Torino
Dipartimento Energia
Fluid Power Research Laboratory
http://www.fprl.polito.it
Influence of the number of chambers (N)
• Same diameter (D)
• Same axial height (H)
• Same displacement
• Ideal timing
• Different eccentricity (e)
Reduction of N
• Higher volume to be filled
• Shorter extension of
suction port
• Larger flow area
• Lower speed of
outer gear
• Lower internal
radius of inner gear
16 / 17

17. Politecnico di Torino
Dipartimento Energia
Fluid Power Research Laboratory
http://www.fprl.polito.it
Conclusion
• Good agreement with experimental results in terms of
evaluation of limit speed for complete filling
• Outcomes from simulations:
• Axial inlet must be preferred (worst case with radial direction)
• The shaped rim is equivalent to a 4 deg delay with radial rim
• Only high delay angles are really effective
• Low speed / high displacement better than high speed / low displ.
• Height must be lowered by increasing the eccentricity
• Small increment of the diameter not necessarily detrimental
• Slight improvement with a few chambers
17 / 17

18. Fluid Power Research Laboratory
www.fprl.polito.it
Politecnico di Torino