5.4.7. Numerical Parameters
All information relevant to iterative schemes (for the F.E.M. task calculations) can be modified in the Numer-ical parameters menu.
Numerical parameters
1. Click Enable evolution on moving boundaries to enable the evolution scheme.
For information on the evolution scheme, see Appendix (p. 192).
2. Specify the evolution parameters.
Modify the evolution parameters
a. Define the starting solution for the iterative scheme in the calculation of the free surface location.
The first calculation is performed at . Increase the value of the initial increment of ( ) to reduce the number of evolution steps and to speed up the calculation.
Modify the initial value of delta-S Polydata prompts you for the initial value of .
3. Click Upper level menu two times to return to the top-level Polydata menu.
5.4.8. Outputs
After Polyflow calculates a solution, it can save the results in several different formats. Choose the one that is appropriate for your postprocessor. In this case, save the outputs in IGES format, as well as the default format for CFD-Post.
Outputs
1. Retain the default output (CFD-Post) and click Enable Iges file output.
The default CFD-Post output is used for postprocessing with CFD-Post. The IGES output contains the modified geometry of the extrudate (after remeshing) calculated at every step of the evolution procedure.
For information on IGES output, see Appendix (p. 192).
Polydata asks you to confirm the current system units and fields that are to be saved to the results file for postprocessing.
2. Specify the system of units for the simulation.
a. Click Modify system of units.
b. Select Set to metric_cm/g/s/A+Celsius.
c. Click Upper level menu three times.
The top-level Polydata menu is displayed.
5.4.9. Save and Exit Polydata
Save and exit
Polydata asks you to confirm fields that are to be saved to the results file for postprocessing.
1. Click Accept.
This confirms that the default Current field(s) are correct.
2. Click Continue.
This accepts the default names for graphical output files (cfx.res) that are to be saved for postpro-cessing, and for the Polyflow format results file (res).
5.4.10. Solution
Run Polyflow to calculate a solution for the model you just defined using Polydata.
1. Run Polyflow by right-clicking the Solution cell of the simulation and selecting Update.
This executes Polyflow using the data file as standard input, and writes information about the problem description, calculations, and convergence to a listing file (polyflow.lst).
2. Check for convergence in the listing file.
a. Right-click the Solution cell and select Listing Viewer....
Workbench opens the View listing file dialog box, which displays the listing file.
b. It is a common practice to confirm that the solution proceeded as expected by looking for the following printed at the bottom of the listing file:
The computation succeeded.
5.4.11. Postprocessing
Use CFD-Post to view the results of the Polyflow simulation.
1. Double-click the Results tab in the Polyflow analysis system. This will start CFD-Post and read the results files saved by Polyflow. CFD-Post reads the mesh information and the solution fields that were saved to the results file.
2. Display the velocity distribution on the boundaries.
Deselect Wireframe in the Outline tree tab, under User Locations and Plots.
a. Click the Insert menu and select Contour or click the button.
b. Click OK to accept the default name (Contour 1) and display the details view below the Outline tab.
c. Perform the following steps in the Geometry tab of the details view of Contour 1:
i. Click the button next to Locations.
ii. Select all topological entities under Fluid Flow Extrusion Polyflow in the Location Selector dialog box (use Shift for multiple selection) and click OK.
iii. Select VELOCITIES from the Variable drop-down list (or by clicking ).
iv. Click Apply.
d. Rotate the image so that you can see the fluid at the inlet of the die, as shown in Figure 5.3: Contours of Velocity Magnitude (p. 183).
Figure 5.3: Contours of Velocity Magnitude
Observe that the velocity is zero along the die wall, as expected, and there is a fully developed profile at the inlet of the die. At the die outlet, the velocity profile changes to become constant throughout the extrudate cross-section. The transition between these two states can be seen in the first third of the ex-trudate.
3. Display contours of velocity in cross-sections.
a. Deselect the contours previously defined.
In the Outline tree tab, under User Locations and Plots, deselect Contour 1.
b. Create the cross-sectional planes, at Z = 0, 3, 7, and 20 cm.
i. Select Plane from the Location drop-down menu ( ).
ii. Click OK to accept the default name (Plane 1) and display the details view below the Outline tab.
iii. In the Geometry tab of the details view, ensure XY Plane is selected from the Method drop-down list.
iv. Enter 0 for Z.
v. Click Apply.
vi. Repeat steps 3.b.i.–v. for the other planes, at Z = 0.03,0.07, and 0.1999 m.
vii. In the Outline tree tab, under User Locations and Plots, deselect Plane 1, Plane 2, Plane 3, and Plane 4.
c. Display the contours.
i. Click the Insert menu and select Contour or click the button.
ii. Click OK to accept the default name (Contour 2) and display the details view below the Outline tab.
iii. In the Outline tree tab under User Locations and Plots, select Wireframe.
iv. In the Geometry tab of the details view of Contour 2, click the button next to Locations.
v. Select all planes under User Locations and Plots (use Shift for multiple selection).
vi. Click OK.
vii. Select VELOCITIES from the Variable drop-down list (or click ).
viii. In the Render tab, disable Lighting.
ix. Click Apply.
Figure 5.4: Velocity Profiles at Cross-Sections (p. 188) shows the velocity profiles at the flow inlet, the flow outlet, and at the planes just before and just after the die exit.
Figure 5.4: Velocity Profiles at Cross-Sections
Compare the velocity profile within the die to the velocity profile just after the die exit at the end of the computational domain. In the die the flow is fully developed. In the extrudate, far away from the die exit, the velocity profile is flat. That is, all the particles in a cross-sectional plane are at the same speed.
Just after the die exit, there is a transitional zone where the velocity profile is reorganized. The velocity profile on the plane Z = 7 cm is no longer fully developed, but it is not yet flat either. The velocity re-arrangement is the source of the deformation of the extrudate.
4. Compare the cross-sectional shape of the extrudate with the die.
a. Simplify the display.
In the Outline tree tab, under User Locations and Plots, deselect Contour 2 and Wireframe.