DIESEL ENGINE: FULL-CYLINDER CLOSED-CYCLE MODEL	Chapter 15
Generating the Closed-Cycle Polyhedral Mesh

Importing a user intermediate surface

The user intermediate surface separates the upper portion of polyhedral cells from the lower portion, thus facilitating the addition and deletion of cell layers. For more information on user intermediate surfaces and a list of important considerations when creating them for your own cases see Chapter 6, “User intermediate surfaces” in the User Guide.

The user intermediate surface for this tutorial is supplied with the STAR-CD installation and should now be imported into es-ice.

•In the Closed cycle polymesh panel, ensure that the User intermediate surface toggle button is selected as shown in Figure 15-13

•Click the ellipsis (...) button next to the Database file box and select uisDiesel.dbs via the file browser

•Click the ellipsis (...) button next to the Database id box and select entry 1 User Intermediate Surface via the database browser

•Click the Add toggle button to add the user intermediate surface shells to the previously created spray zone meshes

•Click Read into general workspace to load the user intermediate surface in the Workspace panel, as shown in Figure 15-14

Figure 15-13 Closed cycle polymesh panel: User intermediate surface

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Figure 15-14 User intermediate surface and spray zones

Checking the spray-optimised zone

If the spray zone intersects the user intermediate surface, es-ice cannot generate a closed-cycle polyhedral mesh. In addition, the spray zone must intersect the geometry surface so that it is trimmed to the injector surface. If there is a gap between the spray zone and the geometry surface, es-ice generates very small polyhedral cells in the gap which can make the solver unstable. Therefore, you should check the spray zone using a section plot before creating the polyhedral mesh. You can also view the position of the spray zone within the engine geometry.

•Specify the section using commands that define a point on the section plane and the direction of the normal to that plane:

SPoint, 0, 0, 0 SNormal, 0, 1, 0

•In the Plot Tool, change the plot type setting to Section as shown in the adjacent screenshot

•Change the Views setting to View 0, 1, 0

•Click the DPlot button to plot the spray zone, user intermediate surface and geometry surface together, as shown in Figure 15-15

Figure 15-15 Section plot of the spray zone, user intermediate surface and geometry

Figure 15-15 indicates that the spray zone does not intersect the user intermediate surface and is positioned correctly within the engine geometry. Figure 15-16 shows that the recess slightly overlaps the injector surface, thus ensuring that the spray zone is trimmed to the injector surface.

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DIESEL ENGINE: FULL-CYLINDER CLOSED-CYCLE MODEL	Chapter 15
Generating the Closed-Cycle Polyhedral Mesh

Figure 15-16 Close-up of spray zone intersecting the geometry surface

Creating the closed-cycle polyhedral mesh

Having obtained suitable spray zone parameters and a user intermediate surface, you can now proceed to generate a polyhedral mesh. At this stage, you should also check the parameters that define an extrusion cell layer on wall boundaries.

•In the Closed cycle polymesh panel, set the Polymesh cell size to 1.2

•Click Extrusion set-up

•In the Polymesh-extrusion panel, check that the parameters are set as follows:

•Global > Thickness: 0.2

•Global > Layers: 1

•Global > Ratio: 1

•Click Create polymesh

Once the child process is complete, the resulting mesh is displayed in the Template panel as shown in Figure 15-17.

Figure 15-17 Closed-cycle polyhedral mesh

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Running Star Setup

Running the Star setup process will store the geometry data obtained so far and generate files required by pro-STAR and STAR.

• In the Select panel, click Star Setup

• In the Star setup panel, deselect the Use unwarper toggle button

• Select pro-STAR 4.20 from the pro-STAR drop-down menu

• Click Star setup

Creating and checking the computational mesh

You can now create the computational mesh at TDC (720 degrees crank angle) and check that it does not contain any negative-volume cells.

•In the Select panel, click Create Result

•In the Create Result panel, select the Interpolate toggle button to interpolate vertex locations between events (as opposed to using internal es-ice smoothing algorithms)

•Ensure that the Use database toggle button is selected so as to store the mesh data to a .dbs file

•Set the Angle (deg) to 720

•Click Create Result to create the mesh at 720 degrees CA. Note that a

result.d720.0.dbs file is added in your working directory. This is a

database-format file containing the mesh at the specified crank angle

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