CFD Mesh Issue and Symmetry Plane Splitting
Tim MacDonald
I had a problem with creating a half mesh recently where the elements on the vertical tail wouldn't match up properly with the elements in the symmetry plane. For example three elements in the tail surface would be connected to a single element on the symmetry plane. This made it impossible to properly create a volume mesh. Changing the meshing parameters didn't seem to help, but I was able to solve the problem by turning on symmetry plane splitting.
My questions are:
Is there a better way to solve this issue? Ideally something I could use through the API. It seems that turning on symmetry plane splitting can't be done this way (I set up a script to change the value in the .vsp3 file directly).
What is the purpose of the symmetry plane splitting option? I'm not very familiar with the details of mesh generation.
Rob McDonald
Splitting on/off, you will get a clue what it does.
The green lines in the attachment represent the symmetry plane that
will be created when this mesh is generated. Here, symmetry plane
splitting is ON. That adds the box around the Pod and also the four
lines connecting the inner box's corners to those of the outer box.
In cases where the outer boundary is very far away (say 100 times a
feature length) -- and has very large edge lengths (compared to those
on the body) -- symmetry plane splitting can be critical.
Without it, CFDMesh would not do a very good job of smoothly growing
the edge lengths on the symmetry plane from near the body to the far
field.
CFDMesh uses a coarse background grid to calculate the target edge
lengths. It is something like 10x10 on each surface patch. With a
large symmetry plane, the background grid won't even notice the body.
It will end up with a target mesh size that is huge everywhere.
By splitting the symmetry plane, CFDMesh breaks the problem into
separate domains -- each one with its own background grid. The
near-body area ensures smooth edge growth near the body.
In general, this won't cause any problems. The only visible change
will be that the split lines persist into the final mesh.
Rob
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