Volume Generation

The final step towards a finished grid is to generate an outer boundary, assign boundary conditions, and generate the volume grid.  The outer boundary is really dependent on the geometry and the problem being solved.  For example, the outer boundary for a supersonic case can be much closer than for a subsonic case.  For illustration, the outer boundary will be 15 body lengths away in all directions.  To start, download the file flying_minnow_clean_split_spaced.igs.gz or continue from the last tutorial.

1.  Read the file flying_minnow_clean_split_spaced.igs.gz in with gluing and trimming enabled. Select the two points shown and  to get an approximate body length.  The message window reports almost 25.5 units long.  Click  to get an approximate center.
2.  Leaving the point created selected, enter 255 (10x25.5) in the  field.  Leave the start and end angles at the default (0 and 90 respectively).  Click .  Select the curve and point shown and go to the Application. Since the rotation is about the x-axis, there is no need to select a vector.  Make sure the VX in  is selected.  Leave the  field at 0.0 but change the   to 90.0 and click  .  and .
3.  Select the surface and point shown and go the Application. Change the  to 90.0.  Change  to 3.  Make sure the VX in vectors component field is clicked to rotate about the x-axis.  Click .
4.  Select the surfaces shown and the point shown.  Change the (VX,VY,VZ) fields in the Vector application to (1,0,0).  Click .  Select the surfaces of the sphere just created, enter "OuterBoundary" in the name field of the group editor area and .  Check the topology and glue the edges of the newly created surfaces.  Click to glue the edges and then click to ensure that the model is topologically valid.
5.  Select the 6 outer boundary points.  Go to the application and enter a value of 30 for the spacing, , and .
6.  In the  application, set the Absolute Initial Spacing to 2.5e-4.  Click the Prop, Body, LeftWing, RightWing, and Mouth groups.  Select  and  and .  Click the OuterBoundary group.  Select  and .  Generate the volume grid by clicking . (This could take a while.  If possible change the host field to another machine).  For illustration,  set only normal growth on groups Prop, Body, LeftWing, RightWing, and Mouth and generate the volume grid again.  (Change the case name in fileio so your previous volume grid doesn't get written over.)  This disables reconnection on the surface grid.  In this case, the volume grid won't generate. (It makes it part of the way and dies).  In some cases, the resulting volume grid is better than with reconnection on.
7.  Read (sm -grid gridfilename)  in the good grid (the one generated with reconnection on).  The group names are not retained so find the group containing the outer boundary, , and.  Make the S_grid Shaded.  In the  application, turn the preview plane on.   Change to the XZ plane,  change the Y value to 0, and .  Turn the preview plane off.
8.  Left click somewhere on the prop close to the cutting plane and zoom.  You can see the viscous packing close to the solid surface.  Set the CuttingPlane to Invisible in the global graphics edit area.  At the top of the panel, select  Volume Weather Map and click .  This gives a plot of the angles in the volume grid.  Click .  This returns the max and min angles to the message window.

This completes the grid generation process.  The various functions in the  panel can be used for quality evaluation.  Practice is the best way to become proficient in grid generation.  Good Luck!