Warning about Symmetry boundary face

[pkck28]

I am running adflow and at the start of the analysis I get a warning:

Symmetry boundary face BC9 of zone domain.00003 is not planar.
Maximum deviation from the mean normal: 7.75206E+00 degrees

I know this is coming from the mesh, but I wanted to know more about this warning and how can I get rid of them. I have following questions about the warning:

• Is mean normal the mean of all the normal of the faces in that particular of zone of the mesh?
• Can I ignore this ignore and not comprise the analysis result?
• How much maximum deviation can be ignored, if ignoring is okay in the first place?

Any help would be appreciated!

[sseraj]

The mean normal is the mean of the face normals in that CGNS block projected in the direction of the symmetry plane normal. As a result, the mean normal points in the same direction as the normal to the symmetry plane.

The effect of non-planar faces on the accuracy of the analysis depends on the size of the block as well as the angle. For example, I have seen a 2 deg deviation on a small block result in almost no change in the output lift and drag. An 8 deg deviation is most likely too large to ignore.

In addition, if you are planning on running shape optimizations with MACH-Aero, any amount of deviation can be problematic. Even small deviations can cause major issues with the volume mesh warping (IDWarp).

[pkck28]

I was able to get rid of those warnings by setting useRotations options as False. Will this have any effect on the analysis result?

Regards,
Pavan.

[sseraj]

If you get non-planar warnings after warping, then it is likely that your baseline mesh is not exactly planar. Even deviations around 1e-3 on the baseline mesh can cause bigger problems after warping. You might find the symmZero function in cgnsUtilities useful. This will exactly zero the symmetry plane.

useRotations mainly affects boundary layer orthogonality, as explained in the options documentation. Even if using "useRotations": False fixes the issue, I would recommend checking the baseline mesh to make sure the symmetry plane is actually planar.

[pkck28]

I changed the value of useRotations to True in USMesh. Then, I used symmZero on the base mesh, but the warning was still present - I think base mesh is good. So, I tried symmZero on the deformed mesh and there were no warnings. This way of dealing with those warnings should be fine, right?

[sseraj]

symmZero is not meant to be used inside the optimization loop but should be okay for analysis. If you are running into this issue repeatedly in an optimization, then maybe just set useRotations to False.

[pkck28]

I am just running analysis, it is not within an optimization loop. Thanks a lot, sabet!