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Old   April 10, 2008, 11:00
Default About the zero eqration mode of transition in CFX
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leo1985
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Hi,everyone. Has anyone used the zero equation model of transition in CFX before? According to the 'ANSYS CFX-Solver Modeling Guide', one can prescribe laminar zones at the leading edges of the wings by setting the intermittency to 0(laminar) or 1(turbulent) over different regions. So what I want to ask is, should I need to write a Fortran routine to setting the intermittency over different regions? Or I can do it with the CEL expressions in CFX? And should I set the intermittency over the whole compute domain,or just near the wall?
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Old   April 10, 2008, 13:04
Default Re: About the zero eqration mode of transition in
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CycLone
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Hi leo1985,

You only need to set it at the wall. If you have geometric regions which delineate the laminar and turbulent parts, you should be able to specify the intermittency directly by inputting a value on boundary conditions associated with each.

If you don't have grid regions, you can do it with a CEL expression. If the geomtry is simple, a step function or linear interpolation function may do, but if it is complex, I would recommend going back to your CAD model or mesh and creating the appropriate regions.

Note that you can also create new regions on your mesh in CFX-Pre, which would allow you to visually pick the areas that are laminar vs. turbulent.

-CycLone
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Old   April 11, 2008, 10:29
Default Re: About the zero eqration mode of transition in
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leo1985
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Thank you very much , CycLone. Now comes the new problem. I just try to set the intermittency on a plane wall, when solving the flow over a plane wall. I use the zero equation mode of transition, and set the intermittency to 0 on one part of the wall and 1 on the other part of the wall by user function (by choosing user function->interpolation->three dimensional->import data from file).The latter part is located downstream of the former part. However, when I see the Turbulence intermittency distribution at the wall in the CFX-post, it doesn't like what I have set them to be. Actually, I think I didn't set the transition position successfully. Why? By the way, are there any examples available showing how to set the transition mode? I have spent so much time on it, God.
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