Thank you for the nice answer! nKnow everythings seems to work fine. I think it was the mesh quality that was not good enough.I have one more question that I already posted but could not solve it. You have in the UserGuide an exaple for the UDS_FLUX. When I use it exacly like it is in the example all my equations diverge. Using the Default mass-flow-rate option for UDS the convergence of residuals is more then enough ( 6 orders and more).Short overview of my Case: 3d, slim Porous media with UDS Source Term (see above), 2 UDS in total, K omega-sst, velocity-Inlet, Pressure outlet. nI use only 2 cells in porous media from porous media inlet, to porous media outlet. Can this be a problem for the UDS_FLUX? I really do not want to use more cells in thickness direction for the porous media. n