Applying a symmetry boundary condition to a surface that is not truly planar will cause an error in the CFX solver. This non-planar condition can be caused either by the geometry or the mesh (e.g. elements not all lying on the surface, which can happen with “tented” elements in ICEM Tetra). The workaround is to assign a free-slip wall. A free-slip wall has all the same attributes of a symmetry surface: No gradients of velocity normal to wall, and no velocity components normal to the wall.