Thanks for the answer !!
Its helpful indeed but I still have a problem. The faces of my interior domain “fluid” overlaps with the outer boundary surfaces and the wing. So when I invert my selection in the Find Data dialog the wing surfaces are not included but the overlapped faces of the “fluid” on the wing are still there, forming again the surface of the wing. If I remove and the interior “fluid” domain I lose my downstream transverse plane (which is the output of the ExtractCellsByRegion).
To help you understand I need to develop a far-field drag post-processing method.
The option to manually select the faces of the cells on the wing (with the select cells through) is not suitable since I need to script my method and I cannot know a priori the id of the wing cells.
Is there any way to split the surfaces of the blocks (symmetry, far-field, wing) and the faces of the grid of the interior domain (fluid) ?