In some cases it is recommended to use Union jack mesh pattern instead of Iso mesh because, if you use Union Jack pattern on the surface mesh, the subsequent volume meshing operation will be more robust and generate good quality tetrahedral elements. If all the faces are iso-meshed it puts lots of artificial constraint on the volume mesher and sometimes it can fail in generating mesh or it can take long time to generate a mesh.
On a more technical note, iso-mesh pattern tends to generate lots of sliver elements and this in turn puts lots of constrain on optimization procedure increasing the overall time of the mesh generation process.
To make it short with union jack pattern:
- Tetrahedral mesher is more robust is generating a mesh.
- Decrease in meshing time
