CFD Analysis of Gerotor Lubricating Pumps at High Speed: Geometric Features Influencing the Filling...
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Transcript of CFD Analysis of Gerotor Lubricating Pumps at High Speed: Geometric Features Influencing the Filling...
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
Politecnico di TorinoDipartimento Energia
Fluid Power Research Laboratoryhttp://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
Politecnico di TorinoDipartimento Energia
Fluid Power Research Laboratoryhttp://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
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Politecnico di TorinoDipartimento Energia
Fluid Power Research Laboratoryhttp://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
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Tip clearanceTooth of the inner gear
Politecnico di TorinoDipartimento Energia
Fluid Power Research Laboratoryhttp://www.fprl.polito.it
Test rig at FPRL
P1
P2P1, P2: miniature pressure transducers on the pump
5 / 17
Politecnico di TorinoDipartimento Energia
Fluid Power Research Laboratoryhttp://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 R21 no no
2 yes no
3 yes yes
R2
R1
Good evaluation of the limit speed
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Politecnico di TorinoDipartimento Energia
Fluid Power Research Laboratoryhttp://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
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2%
Politecnico di TorinoDipartimento Energia
Fluid Power Research Laboratoryhttp://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
Politecnico di TorinoDipartimento Energia
Fluid Power Research Laboratoryhttp://www.fprl.polito.it
Influence of inlet direction
0° : Tangentialcocurrent
direction of rotation
180° : Tangentialcountercurrent
inlet volume
90°
: ax
ial
Max improvement (from 51% to 59%) with axial inlet
radial
axial
9 / 17
Politecnico di TorinoDipartimento Energia
Fluid Power Research Laboratoryhttp://www.fprl.polito.it
Comparison of axial velocity fields
= 90° = 180°
Directionof rotation
Lower contraction coefficient
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15 m/s
0 m/s
Analyzed chamber
Politecnico di TorinoDipartimento Energia
Fluid Power Research Laboratoryhttp://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
Politecnico di TorinoDipartimento Energia
Fluid Power Research Laboratoryhttp://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 theoreticalflow rate (99 L/min)
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Politecnico di TorinoDipartimento Energia
Fluid Power Research Laboratoryhttp://www.fprl.polito.it
H 1
2.5
mm
H 2
5 m
m
10 000 rpm 5 000 rpm
Axial velocity fields
Low axial velocity regions
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Politecnico di TorinoDipartimento Energia
Fluid Power Research Laboratoryhttp://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
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Greater frontal surface
Politecnico di TorinoDipartimento Energia
Fluid Power Research Laboratoryhttp://www.fprl.polito.it
Influence of axial thickness (H)
• Same diameter (D)• Same displacement• Ideal timing• Different eccentricity (e)
15 / 17
Politecnico di TorinoDipartimento Energia
Fluid Power Research Laboratoryhttp://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
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Politecnico di TorinoDipartimento Energia
Fluid Power Research Laboratoryhttp://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
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Fluid Power Research Laboratorywww.fprl.polito.it
Politecnico di Torino