Direct calculation of leakage flux at a synchronous generator using FEM

We simulated a 200MVA synchronous -salient pole- generator, using the 2D finite-element simulation program OPERA (by Vector Fields).

We are trying to determine some parameters of the generator such as transient, subtransient and synchronous reactances as well as time constants by applying a three phase short-circuit at the armature winding.In addition, we would like to estimate by test (if it's possible of cource) the flux leakage distribution in the machine.

Any idea about how to procced the test in order to estimate the flux leakage ?

Thanks in advance!