[RodriguezFatz]

Dear all,

In my RANS simulations I see that the flow in a completely symmetrical diffuser (with symmetrical inlet and outlet boundary conditions) becomes asymmetric in a certain way, please see the picture.
201509281448.png
The simulation starts to converge to the symmetric solution (left picture) but eventually converges to the unsymmetric right picture, where the flow stics to one side of the wall.

By the way, my simulation is 3d, with pipes at inlet and outlet, k-omega-SST or realizable-k-epsilon model.

Can anyone explain why this happens and if this is physically correct? If not, how can I prevent this?

Thanks for any help,
Philipp.