Hello I am a final year university student and am trying to model an annular jet flow expanding into a cylindrical downstream expansion chamber using CFX. The boundary conditions in the expansion chamber are specified as 'Opening' to permit jet entrainment. I am currently having problems getting the solution to convergene (the radial and tangential momemtum eqns) when I make the mesh finer (I am using a structured mesh produced in ICEM). Also the model is a 30 deg wedge segment with periodic boundaries.

As CFX had no under-relaxation factor I have tried changing the Timestep between 10e-3 and 10e-5 in the Solver Options but to no avail. Does anyone have any suggestions? Thanks in advance Richard

Hi,

What Reynolds number? What mesh resolution are you using? What turbulence model? How far downstream is your exit? Compressible or incompressible? Need more details.

And forget about under-relaxation factors. That's from the old days with uncoupled solvers and is very rarely used with CFX these days.

Glenn Horrocks

Thank you Glenn for your response, I stopped playing with under-relaxation factors and instead realised from your further questions that my solution domain was rather small and this was the problem. I have since increased it and found that it now convergenes. Thanks again