Research Papers: Flows in Complex Systems

Method for Fluid Flow Simulation of a Gerotor Pump Using OpenFOAM

[+] Author and Article Information
Robert Castilla

Associate Professor
Universitat Politècnica de Catalunya,
Terrassa ES-08222, Spain
e-mail: robert.castilla@upc.edu

Pedro J. Gamez-Montero

Associate Professor
Universitat Politècnica de Catalunya,
Terrassa ES-08222, Spain
e-mail: pedro.javier.gamez@upc.edu

Gustavo Raush

Associate Professor
Universitat Politècnica de Catalunya,
Terrassa ES-08222, Spain
e-mail: gustavo.raush@upc.edu

Esteve Codina

Universitat Politècnica de Catalunya,
Terrassa ES-08222, Spain
e-mail: esteban.codina@upc.edu

1Corresponding author.

Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received March 15, 2017; final manuscript received June 6, 2017; published online July 21, 2017. Assoc. Editor: Kwang-Yong Kim.

J. Fluids Eng 139(11), 111101 (Jul 21, 2017) (9 pages) Paper No: FE-17-1161; doi: 10.1115/1.4037060 History: Received March 15, 2017; Revised June 06, 2017

A new approach based on the open source tool OpenFOAM is presented for the numerical simulation of a mini gerotor pump working at low pressure. The work is principally focused on the estimation of leakage flow in the clearance disk between pump case and gears. Two main contributions are presented for the performance of the numerical simulation. On one hand, a contact point viscosity model is used for the simulation of solid–solid contact between gears in order to avoid the teeth tip leakage. On the other hand, a new boundary condition has been implemented for the gear mesh points motion in order to keep the mesh quality while moving gears with relative velocity. Arbitrary coupled mesh interface (ACMI) has been used both in the interface between clearance disk in inlet/outlet ports and between clearance disk and interteeth fluid domain. Although the main goal of the work is the development of the numerical method rather than the study of the physical analysis of the pump, results have been compared with experimental measurement and a good agreement in volumetric efficiency and pressure fluctuations has been found. Finally, the leakage flow in the clearance disk has been analyzed.

Copyright © 2017 by ASME
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Fig. 1

The internal gear with trochoidal-teeth profile, where Z is the external gear teeth

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Fig. 2

The mini gerotor pump: (a) 3d-cad model depicting the interprofiles fluid domain, (b) cross section depicting the clearance disk to model axial leakage flow named “couple” disk, (c) outlet and inlet ports, and (d) negative body section depicting the pump fluid domain without any mechanical moving parts

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Fig. 3

Mesh generation process: (a) body pump, with inlet and outlet ports and tubes, with the cylindrical background mesh used with snappyHexMesh, (b) mesh of body pump with cylindrical clearance disk mesh. The interface between the body pump and the clearance disk is an ACMI. (c) Simulation mesh with the three fluid domains: body pump, clearance disk, and interprofiles. The interface between interprofiles mesh and clearance disk is also an ACMI. The only dynamic part is the interprofiles mesh.

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Fig. 4

Logistic function as approximation of step function, as defined in Eq. (2), for kd = 1.5, and k = 5, 10, and 100. d/dmin is the distance between walls normalized with the minimum distance. For the sake of comparison, the normal distribution function is also plotted.

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Fig. 5

Kinematic viscosity distribution in a cross-sectional plane in the middle of the interprofiles domain. Unit of viscosity is m/s2. The minimum value is the usual value for the newtonian fluid, 5.8 × 10−5 m/s2, and the viscous wall model impose high values of viscosity, up to 0.0675 m/s2, when gears are close to each other. Details of sample contact point zones in the interteeth clearance are also shown.

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Fig. 6

Mesh deformation with moving boundary points. The top image is the mesh for initial time. The bottom three images show the mesh when time is 25% of gearing cycle period. (a) Deformed mesh with points moving with geometry, (b) slip movement, mesh is not moving and its relative position is the same as in the initial time, and (c) combination of angular movement with slip: the mesh is moving with the contact point angular velocity. Magnification of critical mesh zone is displayed for the sake of clarity. It is obvious that the third procedure, used in the present work, is the best for mesh quality conservation.

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Fig. 7

Scheme of the new approach for the dynamic mesh. The velocity of the boundary points is an hybrid between transport with geometry (vg) and a slip velocity in order to keep the mesh with a prescribed mesh velocity vm.

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Fig. 8

Scheme of the simulation process. The three mesh parts are generated with snappyHexMesh, blockMesh, and netgen, and linked together with ACMI. The new presented models for wall motion and contact point in the inter-profiles mesh are also displayed.

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Fig. 9

Numerical flow ripple at outlet port for 1000 rpm and 1 bar working pressure with interteeth contact

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Fig. 10

Flow rate in the clearance disk. This flow rate has been computed by integrating, for each time step, the main flow velocity component of the leakage flow in the clearance disk, in the plane depicted in Fig. 3(b).

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Fig. 11

Pressure distribution in the middle plane of clearance disk. The times are (a) (1/6) Tg, (b) (1/3) Tg, (c) (1/2) Tg, (d) (2/3) Tg, (e) (5/6) Tg, and (f) Tg, where Tg is the gearing period. The gears are rotating counterclockwise and the flow is upwards in the figure. The minimum pressure value is −21.5 kPa and the maximum value is 107.5 kPa.

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Fig. 12

Main flow component velocity distribution in the middle plane of clearance disk (see Fig. 3(b)). The shown times are (a) (1/6) Tg, (b) (1/3) Tg, (c) (1/2) Tg, (d) (2/3) Tg, (e) (5/6) Tg, and (f) Tg, where Tg is the gearing period. The gears are rotating counterclockwise and the flow is upwards in the figure. The values of main flow velocity component are 0.5 m/s and −1.5 m/s. Note that spots in the right part of the pictures at the beginning and the end of the gearing process. It denotes higher leakage, which agrees with leakage flow rate in Fig. 10.

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Fig. 13

Test bench hydraulic scheme

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Fig. 14

Experimental and computational flow ripple time series at outlet pressure port for 1000 rpm and 1 bar of working pressure. Pressure data are fluctuations over average pressure (1 bar). Time has been normalized with gearing period Tg.



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