Using principal stresses
 

Dear CFX users,
in an attempt to add a source term for fluid degradation, I should get hold of max and min eigenvalues for a [tensor] cell. It seems the eigenvalues in this case also can be called Principal stresses. Ansys Help do have traces of Principal stresses (i.e the section about "Ansys files"), but no real documentation of how to use this, or if it is even possible in CFX. I was hoping to use some existing functions for this, and the u.grad_x etc. are tempting, but perhaps only gives normal stresses, not principal stresses.

(I am not even able to find documentation on the .grad_x functions and similar, any idea where that is found? Was hoping to look there for further help.)