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Old   September 23, 2015, 15:14
Default Free Surface Convection Model
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robo
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Hey, can anyone tell me what CFX is actually doing when it solves free surface flows? I know that it's using a VoF approach, but the theory manual only says that it uses "some special discretization options to keep the interface sharp" including "A compressive differencing scheme". Is it using cicsam or something like that? I need to know what actual discretizations are being done on the convective term in the VoF equations. The theory manual seems to be pretty much useless at actually describing the theory...
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Old   September 26, 2015, 20:43
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No it is not using CICSAM. Also, do not expect to have the entire theory behind it explained. It is commercial software and they choose to keep some details confidential.

I think the CFX training courses have some more detail about the implementation. Maybe ask your CFX support person about it.
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Old   September 29, 2015, 14:18
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If you know it's not CICSAM, does that mean you know what it is?

I appreciate your taking the time to respond, but I find your answer pretty frustrating. I'm not asking for the implementation algorithm or some sort of special secret sauce. If a company is going to keep their discretization techniques confidential, then I don't see how they can expect people to be able to do academic work with their product. It's not like this is some bizarre standard to expect either; this info is available from competing codes such as Fluent, including the citation of the academic papers.

I will see if I can get the answer from our support person. Thanks again.
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Old   September 29, 2015, 18:39
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Sorry about the frustrating answer. I did look into this area many years ago but it has been so long I cannot recall the exact details so I am sorry if my answer is a bit vague. The default compressive scheme is not like the surface sharpening algorithms in Fluent (CICSAM, Geo Reconstruct) - but I recall it is similar to HRIC. But it has been so long I cannot be more specific.

Also, I have just had a quick look in the documentation and cannot find anything about the compressive scheme (other than it is used for volume fraction advection)

There is the interface compression level setting - but there is no documentation about exactly what it does.

Yes, your best bet is ANSYS support.
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Old   September 30, 2015, 08:01
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No worries about the answers, not your fault that the theory documents aren't a bit better. Thanks again for all your help.
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