SimScale CAE Forum

|| Dale's Feature Poll - Allow a face to be assigned as a slip wall and also a symmetry plane, the way it used to be 🙏


EDIT: This has been turned into a feature request since the new way of disallowing a face to be both a slip wall and a symmetry plane always results in no-slip walls on the symmetry plane, if you use a symmetry plane.

The topic posts discuss the issue.

  • I would like to be able to assign a face as a slip wall and a symmetry plane.
  • I am OK if all my symmetry planes defined by faces are automatically (and permanently) set to no-slip walls.

0 voters

A few months ago I ran many incompressible external simulations where my symmetry plane was also a face of the Background Mesh Box.

Now when I try to run a new simulation in those projects I get this error:

The face in question is a background mesh box face and it is my symmetry plane AND a slip wall.

If I can no longer use a background mesh box face as my symmetry plane, how do I assign a symmetry plane?

OR, do I even need a slip wall on the symmetry plane?



Hi Dale,

you can simple use that face as a symmetry plane and leave the other ones as slip, that’s fine. To be safe here share the project with me (if that’s not the other one we already talked about) and I will have a look at the setup.




Yes, so I tried not making the symmetry face a slip wall and got what appear to be good results :slight_smile:

Here is the updated and renamed project.



So in a private project I have looked a little further into this problem and I DO see a problem in that if I use the face only as a symmetry plane, the results show that there is a boundary layer on that plane which is NOT acceptable.

I am unable to post process that public project any more so I am not able to show you the above fact (which is another problem which maybe you could look at).

SO, my first post is still valid and simply using the face as a symmetry plane is not acceptable, it also needs to be a SLIP wall . EDITED (used to say no-slip here).

Any further ideas?



Hi Dale,

Why do you think that the boundary layer is not valid? Also the symmetry plane has to be a symmetry boundary condition as the name implies - a no-slip condition is zero velocity at the walls which is not the case for you I guess?!




Sorry, my error, I will fix my post.

I need slip wall on symmetry plane but when you just use a face as a symmetry plane, the default is a no-slip wall.


A no-slip wall on a symmetry plane does not have sense to me. This prevents air from coming down the symmetry plane surface (or near it) at the speed it should when it hits the geometry faces at the symmetry plane.

Not sure if I said that correctly.


Hi Dale!

It indeed is unphysical in your case (cannot think of one where this should be correct anyway). Also inflated boundary layers have to be added do your geometry - think you have experimented with this quite a lot before :wink:




Yes I am using inflated boundary layers. But I still think the symmetry plane should not be inflated.

My current workaround is that I just stopped using symmetry planes.

So far I do not see any problems with this workaround, can you think of any?

Edit: Bump


Hi Dale,

the mesh right now looks fine except around your object in the regions perpendicular to the plane as well as the z direction. I would extend the directions and make sure the mesh fineness will be increased as I think this is too coarse at the moment, BLayer looks good and only has to be applied to the object and not the symmetry face.





Thanks for those comments but I was looking for feedback regarding the fact that I no longer use symmetry planes in my simulations, I just have a slip wall bounding box face that splits my full geometry. This project only shows the incorrect use use a symmetry plane which nowadays results in the symmetry face being a no-slip wall.




I turned this into a ‘Dale’s Feature Request’ topic since I there is no way to currently have a slip wall symmetry plane. :frowning: