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How to discard highly skewed cells from the mesh
Sometimes one ends up with a volume mesh that has a few highly skewed cells.
If such cells are in an unimportant part of the flow field, it is quicker to discard them
(i.e. move them out of the domain) rather than trying to fix the mesh.
There are several possibilities for quickly fixing/deleting highly skewed cells in
The following steps can be conducted in TGrid:
1) If the highly skewed cells are close to the boundaries of the domain,
first try using the Mesh -> Tri/Tet -> Boundary Slivers panel in TGrid to get
rid of them. This procedure is detailed in section 6.2.5 of the manual.
2) If there are just a few of these cells (<10) you can try and modify them
manually. First use the text command
to find out the names of the skewed cells. Then display them one by one.
Use the boundary modify panel to move nodes of the cells to reduce the
Note that this method is tedious and risky. If the node is moved too much
the mesh will get corrupted.
3) The third option is to separate the highly skewed cells into a new cell zone
and delete that cell zone. This is usable only if the cells are in an
unimportant region of the flowfield.
If all the highly skewed cells lie in one specific region of the flow domain,
we can select the region and split it into a separate cell zone as follows:
Go to Boundary - > Refine - > Define
Enter extents of the region that you want to separate
Go back to the Boundary - > Refine panel
Select the newly created region and hit Mark (The new region is now
marked for further operation.)
Use the text command /mesh/modify/separate-cell-by-mark to
separate the cells marked into another zone.
Delete that zone or make it solid
4) Another option if the highly skewed cells are in an
unimportant region of the flowfield is to open the mesh
in Fluent and do the following: (Here you can select cells
based on skewness.)
- Go to Adapt -> Iso-Value (Remember to initialize before this)
- Mark cells in the desired range of skewness
- Go to Grid -> Separate and separate the cell zone based
on the marked cells register
- The skewed cells are all in the separate cell zone now,
they can be deleted using Define> Delete cells in Fluent 6.1.22
and versions above.