T utorial: V ane Pump Modeling in ANSYS FLUENT
In tro duction
This tutorial illustrates how to setup and run a vane pump analysis in ANSYS
FLUENT 13. This tutorial demonstrates how to do the following:
? Create an initial mesh.
? Set up a problem for a dynamic mesh.
? Specify the motion of dynamic zones using a compiled user-defined function (UDF).
? Preview the dynamic mesh before starting the calculation.
? Perform transient dynamic mesh calculation.
? Postprocess the resulting data.
Prerequisites
This tutorial assumes that you are familiar with the FLUENT interface. Some of he basic steps in the setup and solution procedures will not be shown explicitly.
You should be familiar with the dynamic mesh model and UDFs. Refer to the FLUENT 13 User’s Guide and the FLUENT UDF Manual for more information.
Problem Description
A vane pump consists of a rotor with radial slots positioned off-center in a housing bore.
A generic vane pump geometry is shown in Figure 2, where the rotor and housing are both
circular. Vanes that fit closely in rotor slots slide in and out as the rotor turns. Pumping action is caused by the expanding and contracting volumes contained by the rotor, vanes and housing.
Meshing Requiremen ts
In this tutorial, a UDF is used to dynamically move the mesh at each time step. Hence, follow some specific meshing rules so that both the initial mesh and all subsequen t motion is correct. With this meshing process, the pump core can be meshed with a high aspect ratio map mesh sc heme.Eac h mesh node displacemen t is composed of a solid body rotation and a radial translation. The node displacemen t is
a function of eccentricity, rotational speed, and rotor/housing diameters. The pump gap (if created) is also meshed and moved in a similar manner to the core. The meshing requirements (Figure 1) are as follows:
? Rotation must be about the z-axis.
? The origin must be located on the cylindrical axis of the rotor (i.e., the small circle or profile).
? The pump housing (i.e., the large circle or profile) must be placed to the left
of the rotor and have a y-coordinate equal to zero.
? If pump contains gaps, one gap must be placed on the positive x axis.
? The vanes must be equally spaced.
? The pump core must be defined as a single fluid zone.
? If the pump contains gaps, all the gaps must be defined as a single fluid zone.
Figure 1: Meshing
Requiremen ts
R=radius of pump housing (if applicable), housing may be a profile
r=radius of rotor
d=offset
w=vane width
The schematic of the pump is shown in Figure 2. The meshed vane pump geometry of the circular housing is shown in Figure 3. The pump core is meshed with a mapped mesh scheme. The pump gaps are meshed using a high aspect ratio mapped mesh scheme. The inlet and outlet pipes are meshed with a tetrahedral mesh. The gaps and inlet/outlet pipes are connected to the pump core using non-conformal grid interfaces.
Figure 2: Problem Schematic
Figure 3: Meshed Vane Pump (Circular Housing)
3
Figure 4: Mesh Detail for Single V ane
Preparation
1. Copy the files circle-pump.msh, input.txt, vane.c, gerotor_vane_smoothing.c and
tait.c to your working folder.
Note: The input file must be called input.txt and must be located in the same folder as the case file.
2. Start the 3D (3d) version of FLUENT.
Step 1: Grid
1. Read the mesh file circle-pump.msh.
File Read Mesh...
FLUENT will read the file and report the progress in the c onsole.
Step 2: General Settings
General Scale
1. Change the grid units to mm.
(a) Select mm from the Mesh Was Created In drop-down list in Scaling group box.
(b) Select mm from the View Length Unit In drop-down list
Note: Do not scale the grid.
(c) Close the Scale Grid panel.
General Display
(a) Retain the default parameters.
(b) Click Display.
Figure 5: Grid Display
Use the right mouse button to check which zone number corresponds to each boundary.
If you click the right mouse button on one of the boundaries in the graphics window, its zone number, name, and type will be printed in the FLUENT c onsole.
Note:User-Defined F unction In pump models without gaps, incompressible liquid and constricting volumes create unphysical pressure spikes. Adding liquid compressibility through a UDF provides a realistic solution. If the pump contains gaps, this liquid compressibility UDF is not required as any pressure increase in the liquid will cause it to escape through the gaps.
The model here contains gaps; hence it is not necessary to use the compressibility UDF. However, the compressibility UDF is included for completeness, though it will not be used by the solver. The file input.txt is read w h e n the UDF is loaded. This cont ai ns the parameters required for the UDF (see Appendix 1). All inputs to the file input.txt must be in SI units.
General
(a)Select Transient from Time
(b)Retain the default values for the other parameter.
Step 3: UDF
1. Compile the UDF library using the source files vane.c, gerotor_vane_smoothing.c and
tait.c.
Define User-Define Functions Compiled…
(a) Click the Add... button to open the Select File panel.
i. Select the source files, vane.c, gerotor_vane_smoothing.c and tait.c and click
OK.
(b) Click Build to build the directories.
(c) Read the information in the Information panel and click OK.
(d) Click Load to load the UDF.
Step 4: Models
Models
1. Enable the standard k- epsilon turbulence model.
Models Viscous Edit
(a) Select k-epsilon (2 eqn) in the Options group box.
(b) Retain the default values for the other
parameters.
(c) Clic k OK to close the Viscous Model panel. Step 5: Materials
Materials
Materials Fluid Create/Edit
(a) Delete air from the Name entry box and enter oil.
(b) Enter 0.008for Viscosity.
(c) Select user-defined from the Density drop-down list to open the User-Defined Functions
panel.
i. Select tait_density::libudf and click OK to close the User-Defined Functions panel.
(d) Click Yes in the dialog box that opens to overwrite air.
(e) Select user-defined from the Speed of Sound drop-down list to open the User-
Defined Functions panel.
i. Select tait_speed_of_sound::libudf and click OK to close the User-Defined
Functions panel.
(f) Click Change/Create an d close the Materials panel.
Step 6: Boundary Conditions
Boundary Conditions Inlet
(a) Select Intensity and Hydraulic Diameter from the Specification Method drop-down
list in the Turbulence group b o x.
(b) Set the Turbulent Intensity to 5%.
(c) Set the Hydraulic Diameter to 12 mm.
(d) Click OK to close the Pressure Inlet panel.
Boundary Conditions outlet
(b) Select Intensity and Hydraulic Diameter from the Specification Method drop-down list
in the Turbulence group b o x.
(c) Set the Backflow Turbulent Intensity to 5%.
(d) Set the Backflow Hydraulic Diameter to 10 mm.
(e) Click OK to close the Pressure Outlet panel.
Step 7: Grid Interfaces
Mesh Interface Create/Edit
1. Create an interface called intf-gap.
(a) Select intf-pump-gaps from the Interface Zone 1 selection list.
(b) Select intf-pump-vanes from the Interface Zone 2 selection list.
(c) Enter intf-gap for Grid Interface.
(d) Click Create.
Note: When you select intf-gap in the list of created interfaces, Boundary Zone
1 and Boundary Zone
2 should show wall-14 and wall-15 r espectively.
2. Create an interface called intf-pump.
(a) Select intf-pump-pipes from the Interface Zone 1 selection list.
(b)Select intf-pump-housing from the Interface Zone 2 selection list.
(c) En ter intf-pump for Grid Interface.
(d) Click Create and close the Grid Interfaces panel.
Step 8: Dynamic Mesh
Dynamic Mesh
(a)Enable Dynamic Mesh and In-Cylinder in the Models group b o x.
(b) Click the In-Cylinder tab and specify parameters as shown in the table:
P arameter Value
Crank Shaft Speed500
Starting Crank Angle0
Crank P erio d360
Crank Angle Step Size0.25
(c) Click OK to close the Dynamic Mesh Parameters panel.
Dynamic Mesh Create/Edit
(a) Select fluid-pump from the Zone Names drop-down list.
(b) Select User-Defined in the Type group b o x.
(c) Click the Motion Attributes tab and select vane pump core::libudf from the Mesh
Motion UDF drop-down list.
(d) Click Create.
(e) Select fluid-gap from the Zone Names drop-down list.
(f) Select User-Defined in the Type group b o x.
(g) Click the Motion Attributes tab and select vane pump gap::libudf from the Mesh
Motion UDF drop-down l ist.
(h) Click Create.
(i) Similarly, create the dynamic zones for inner-gap-wall, pump-rotor, wall-14, and
wall-15 by selecting the UDF walls::libudf.
(j) Close the Dynamic Mesh Zones panel.
Step 9: User-Defined Function Hooks and Memory
1.Set the initialization function hook.
Define User-Defined Function Hooks
(a) Select init sector::libudf for Initialization.
(b) Click OK to close the User-Defined Function Hooks panel.
2.Define one user-defined memory location.
Define User-Defined Memory…
(a) Increase the Number of User-Defined Memory Locations to 1. (b)
Click OK to close the User-Defined Memory panel.
Step 10: Solution
Solution Methods
1. Select PISO transient algorithm.
(a) Select PISO from the Pressure-Velocity Coupling drop- down list.
(b) Retain the default values for other parameters.
Solution Controls
(a) Keep the default values
Monitors
(a) Enable Plot in the Options group b o x.
(b)Click OK to close the Solution Controls panel.
Solution Initialization
(a) Click Initialize and close the Solution Initialization panel.
FLUENT warns (in the console) that you should display the UDM-0 using cell value to verify that the sector numbers are calculated correctly.
Display contours of UDM-0 (Figure 6).
Note: This should always be done after setup and initialization to verify that the
se ctor numbers are c orr e ct.
(a) Enable Filled and disable Node Values in the Options group box.
(b)Set Levels to 8.
(c) Select User Defined Memory... and User Memory 0 from the Contours of drop-down
lists.
(d) Select intf-pump-housing, intf-pump-vanes, and wall: 0 from the Surfaces
selection list.
(e) Click Display.
For better rendering of the image, enable Headlights On in the Lights panel, sele ct
‘Phong’ from the Lighting Method drop-down list and click Apply.
Figure 6: UDM-0
Sectors
Save case and data before Mesh Motion Preview with circle-pump.cas.gz and circle-pump.dat.gz.
Calculation Activities Edit
Perform mesh motion preview for 20 time steps.
Dynamic Mesh Preview Mesh Motion…