Hello, Please help me on this subject: I have read the Star-CD manual and some of tutorials but I couldn't undrestand when really we need to define the Coupling between different cells, for exapmle when we do refining, should we do that or not?

Thanks in advance, Mehdi

You will need coupling, when there is a non-conformal grid. That is, when there is no 'node to node connectivity'. This comes into picture when two or more different mesh geometries are assembled, forming a non-conformal interface. Hope this clarifies.

For any case, check the cracks. And the cells for which couples are required to be generated will be displayed automatically. Cracks can also occur due to non merging of vertices so do merge the vertices before checking for the cracks