Boundary edges not recognized


I’m trying to extract the airfoil surface from my unstructured data set to plot Cp over airfoil surface. I was following the procedure given in:

but when I select boundary edges and then I try to extract cells by region none of the edges are recognized.

My case is unstructured and 3D whilst the case given in the topic is 2D

Any idea on how to solve?
Is there any other option which I have to use given that my case is 3D?


If you have a 3D mesh and want a surface, then you probably want to skip the Feature Edges step.

You didn’t post your data nor even show a diagram or image, so I have to guess what your data looks like. I’m guessing the airfoil you want to see is a hole in the middle of your mesh. In that case, Extract Surface should generate this surface. But it will also generate the outer surface that envelops it, so you won’t see it. If you fly the camera inside the outer envelope, you should be able to see the airfoil in the middle. As described in the other page, you can use tools like Extract Cells By Region or Clip to remove the outer envelope.

Sorry for the few information I gave, you got everything right about my domain.
I was messing around and I’ve got to this point


I only have to remove spurious cells now, any help on that would be appreciated


My guess is that those spurious cells come from discontinuities in the mesh. That is, there are 2 polyhedra that are supposed to share a face, but the topology connection is not correct. Usually this is from errors in the mesh although discontinuous methods might do this on purpose.

You can try using the Clean to Grid filter (before Extract Surface) to merge coincident points and hopefully get shared faces to be shared topologically.

This is indeed for DG type solver but the Clean to Grid filter before Extract Surface has been already applied but was not successful (see on the left the pipeline browser)

You could try using the Connectivity filter to identify and extract the largest connected surface, which should be the airfoil after clipping.

Getting closer but still issues on the Leading Edge zone

At least one of those cells must be touching the airfoil. I can’t think of any automatic way of removing those. My only thought is to remove them with an Extract Cells By Region with a carefully placed plane.