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Convergence of an Annular Jet Model

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Old   February 28, 2007, 06:38
Default Convergence of an Annular Jet Model
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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
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Old   February 28, 2007, 17:21
Default Re: Convergence of an Annular Jet Model
Glenn Horrocks
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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
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Old   March 1, 2007, 12:59
Default Re: Convergence of an Annular Jet Model
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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
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