The interfere of Periodic with symmetry boundary conditions
 

Hi
I'm using a house made c++ code for numerical simulation of Navier-stokes. The code has been validated alot and lot's of publications has been made based on results taken from this code. But i have a problem with implementing both Periodic and symmetric boundary conditions. Considering a channel with periodic boundary condition in x direction and symmetry (free-slip) boundary condition in y direction.The results of solving half of the domain is not in agreement with whole domain. In the cases without periodic boundary condition, symmetric solution is in totall agreement with whole domain but when i implement periodic BC, the results (of symmetric solution) are not acceptable. SO i thought it might be sth with interference of Periodic and symmetry BCs simultaneously.

has anyone had the same experience?!
regards and thanks in advance:)