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

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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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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



Test rig at FPRL

P1

P2P1, P2: miniature pressure transducers on the pump

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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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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%



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)

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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

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Comparison of axial velocity fields

= 90° = 180°

Directionof rotation

Lower contraction coefficient

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15 m/s

0 m/s

Analyzed chamber



Influence of inlet port profile

= 0° Ideal timing > 0° Closing delay

Radial inlet pipe

Flow area of a chamber

Volumetric efficiency

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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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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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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



Influence of axial thickness (H)

• Same diameter (D)• Same displacement• Ideal timing• Different eccentricity (e)

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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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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

cfd analysis of gerotor lubricating pumps at high speed: geometric features influencing the filling...

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