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Doubts UDS Flux, UDS Unsteady for VOF model

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Old   March 17, 2010, 09:53
Question Doubts UDS Flux, UDS Unsteady for VOF model
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Kelvin Loh
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Hi all,

Have some questions regarding how Fluent treats the UDS for its VOF model.

1. For the standard UDS, it's quite clear that the phi variable is multiplied by the volume fractions of each phase depending on whether it is solved in the primary, secondary, or mixture domain. But if I were to provide my own unsteady and convective terms via UDF, then is the phi variable multiplied by the cell VOF values as well? or do I have to obtain the cell VOF value then multiply it explicitly in my UDF?

2. For the UDS diffusivity, I seem to have some trouble defining the mixture diffusivity. In the manual, it says that if I were to specify the UDS diffusivity for the individual phases, FLUENT would automatically do an algebraic mean of the diffusivity at the interface, however, when I checked it after initialization, the whole domain has a UDS diffusivity value from either the primary fluid or the secondary one. This seems to contradict what the manual says. Please do enlighten me on this issue? Also, if I were to use DEFINE_DIFFUSIVITY in my UDF, are the cell diffusivity values treated the same way(i.e. taking algebraic mean for VOF values between 0 and 1)? or I should do the algebraic/harmonic (preferrable) mean in the UDF?

3. Has anyone here successfully implemented a discontinuous concentration profile across a water-gas interface? Would you mind pointing me to the right direction?

Thank you

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