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Simulation of a Vane-type Oil Pump Transient Computation with Morphing Thomas Fischer, Daimler AG, Berlin Plant, ES Dr. Ulrich Stubbemann, Daimler AG, Berlin Plant, ES Jan Fischer, Daimler AG, Berlin Plant, EV/T Kai Fellmann, Daimler AG, Berlin Plant, EH
Simulation of a Vane-type Oil Pump | Daimler AG Berlin Plant | 20.03.2012 2
Outline 1. Introduction
• Structure and Function of the Vane-type Pump
• Assignment for the CFD Simulation with STAR-CCM+
2. Construction of the Simulation Model in STAR-CCM+
3. Selected Results of the Simulation
4. Summary
Simulation of a Vane-type Oil Pump | Daimler AG Berlin Plant | 20.03.2012 3
Introduction
Structure and Function of the Vane-type Pump Assignment for the CFD Simulation with STAR-CCM+
Simulation of a Vane-type Oil Pump | Daimler AG Berlin Plant | 20.03.2012 4
Structure and Function of the Vane-type Pump
The fluid is sucked in and displaced by the change in volume of the chambers.
Motions
•Rotation of the pump rotor and the vanes
•Translation of the vanes in the pump rotor
1. Introduction
Translation Rotation Pressure delivery side
Intake side
Simulation of a Vane-type Oil Pump | Daimler AG Berlin Plant | 20.03.2012 5
Pressure Pulsation of the Vane-type Pump
Assignment for the CFD Simulation with STAR-CCM+
• How high is the dynamic component stress because of the pressure pulsation?
• Can the effect of modifying the geometry on the pulsation be assessed without elaborate measurements?
1. Introduction / Assignment for the CFD Simulation
7.52 7.528 7.536 7.544 7.552 7.56
time [s]
-2
0
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14
pres
sure
[bar
]
1D Simulation
67.5 67.51 67.52 67.53 67.54 67.55-4
-2
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pres
sure
[bar
]
Measure
Inlet Outlet
Graph of the pressure in a delivery chamber versus the time
The pressure curve is governed by the connection of the chamber with the inlet or outlet.
This pressure change is called pressure pulsation.
Simulation of a Vane-type Oil Pump | Daimler AG Berlin Plant | 20.03.2012 6
Cavitation Damage at the Set Collars
Assignment for the CFD Simulation with STAR-CCM+
• What mechanism causes the implosion of the gas bubbles at this position?
• Can the effectiveness of geometrical modifications be assessed without elaborate endurance testing?
1. Introduction / Assignment for the CFD Simulation
The endurance test yields cavitation damage at the set collars of the vane-type oil pump.
Simulation of a Vane-type Oil Pump | Daimler AG Berlin Plant | 20.03.2012 7
Pressure Activation of the Vanes
Assignment for the CFD Simulation with STAR-CCM+
• How must the oil feed be arranged in order to obtain an optimal pressure distribution in the interior of the rotor?
• What pressure (force) is actually applied to the undersides of the vanes?
1. Introduction / Assignment for the CFD Simulation
The vane must lie on the contact surface of the set collar in each operating state.
The vanes are therefore activated by pressure at the undersides.
Pressure activation of the vanes
Simulation of a Vane-type Oil Pump | Daimler AG Berlin Plant | 20.03.2012 8
Construction of the Simulation Model in STAR-CCM+ Construction of the model Preparation of the simulation Sequential control
Simulation of a Vane-type Oil Pump | Daimler AG Berlin Plant | 20.03.2012 9
Basic Settings for the Mesh and Physical Continua
Physical continuum Segregated flow
User-defined density (compressible fluid)
Implicit unsteady
Mesh continuum Polyhedral mesher
Prism layer mesher
Surface remesher
2. Model Construction
Geometry regions
Mesh Fixed region
Morphed region
Interfaces
Simulation of a Vane-type Oil Pump | Daimler AG Berlin Plant | 20.03.2012 10
Definitions of the Regions and Motions in STAR-CCM+
•Splitting of the moving region into boundaries
•Assignment of the motions to the individual boundaries
Morpher: Motion
Rigid motion: Rotation
Incremental displacement: Table with local coordinate system
2. Model Construction
Simulation of a Vane-type Oil Pump | Daimler AG Berlin Plant | 20.03.2012 11
Definitions of the Regions and Motions in STAR-CCM+
•The mesh quality deteriorates as the rotational angle increases. Remeshing occurs if impermissible cells emerge.
•The boundaries are deformed. The deformation of the boundaries is retained in the remeshing.
To keep the deformation within acceptable limits, new meshes must be imported.
2. Model Construction
10° 18°
Simulation of a Vane-type Oil Pump | Daimler AG Berlin Plant | 20.03.2012 12
Preparation of the Parametrized Surface Model in CAD
•The boundaries are generated in the CAD model - Splitting and naming the boundaries is not required in STAR-CCM+.
- Meshes can be automatically generated with little effort for fixed positions.
• The CAD model is parameterized - The positions of the geometry can be easily generated in the parameterized CAD model.
2. Model Construction
Simulation of a Vane-type Oil Pump | Daimler AG Berlin Plant | 20.03.2012 13
Preparation of the Control Point Tables
• Analytical computation of the control point coordinates from the geometry data of the pump
• Computed are tables for the translation of the vanes and the rotation of the chamber
• The number of control points is critical; to be weighed is the geometrical distortion compared with the CPU time for the morphing
• For the rotational range of the fluid, control points for 1° rotational angle and 1 mm chamber depth are computed ~8300 points
• In addition for the vane displacement, one point for each vane and each time increment
2. Model Construction
Simulation of a Vane-type Oil Pump | Daimler AG Berlin Plant | 20.03.2012 14
Sequential Control via JavaScript 2. Model Construction
Start
> 5 turns?
< 1 turn?
< 10°?
Reset history
End
Remeshing Read prepared
Mesh
Morphing
Simulation step
Error?
Yes
No
Yes
Yes
Simulation of a Vane-type Oil Pump | Daimler AG Berlin Plant | 20.03.2012 15
Motion of the Mesh 2. Model Construction
Assessment of the mesh quality by means of a test calculation.
Simulation of a Vane-type Oil Pump | Daimler AG Berlin Plant | 20.03.2012 16
Selected Results of the Simulation
Simulation of a Vane-type Oil Pump | Daimler AG Berlin Plant | 20.03.2012 17
Flow Rates in Selected Levels
3. Results
The area of the observed cavitation damage is characterized by a directed flow.
Section plane in the area of the observed cavitation damage
Simulation of a Vane-type Oil Pump | Daimler AG Berlin Plant | 20.03.2012 18
Flow Rate Distribution in the Selected Section Plane and Pressure Distribution at the Set Collar
3. Results
The area of the observed cavitation damage is characterized by a directed flow.
Section plane in the area of the observed cavitation damage
Simulation of a Vane-type Oil Pump | Daimler AG Berlin Plant | 20.03.2012 19
Average Pressures at Selected Surfaces Pressure Distribution
The pressures averaged at the surfaces yield the component stress due to the pressure pulsation.
The pressure activation of the vanes is computationally optimized, significantly reducing the testing labor.
3. Results
0
1
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10
0,00E+00 4,55E-03 9,09E-03 1,36E-02 1,82E-02
time [s]
pre
ssu
re [
bar]
pressure pumpoutlet
pressure vane topside
pressure vanebottom side
pressure vane frontside
T=120 °C
n=3300 rpm
Simulation of a Vane-type Oil Pump | Daimler AG Berlin Plant | 20.03.2012 20
Summary • The presented procedure requires about 14 days for constructing the
CFD model and calculating an operating point.
• The coupled preparation of the meshes in the CAD system and in STAR-CCM+, combined with the specified morpher settings, allows good mesh quality of the moving region.
• The results of the computation provide answers to the questions raised: - The dynamic component stress due to pressure pulsation is computed as a surface integral.
- The pressure activation of the vanes is computed and optimized.
- Flow phenomena leading to cavitation damage become visible.
- Geometrical variations can be assessed computationally.
• The transient CFD computation of the pumps significantly reduces testing labor.
• The computation was introduced as a standard in the pump development.
4. Summary