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Old   June 23, 2010, 03:34
Default Periodic BC for VOF
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Raghvendra Gupta
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Dear All
I am trying to write a small UDF to define periodic boundary condition while using VOF as Fluent does not allow its periodic bc to be used while using VOF.
My problem is simplified in the sense that I always have only one phase present at the inlet and outlet at all teh times so I dont need to wrap volume fraction but only velocity.
The complication is that I have positive and negative both velocities at the exit (and inlet) boundaries.
I have started with writing a small udf where we write back the velocities from outlet to the corresponding inlet element and this works fine for single phase flow unless we have a positive velocity (no backflow) but as soon as I define a profile which has backflow (with wall moving backwards), the solution starts diverging.
I am using velocity inlet and pressure outlet as boundary conditions.

Any comments and ideas are welcome.
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Old   June 23, 2010, 07:32
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my only idea is the velocity inlet might be the problem, because of the adhesion condition at the wall... I hope that helps, good luck...
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Old   June 23, 2010, 16:04
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Raghvendra Gupta
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dear oxmox
what do u mean by that? If you are talking about the singularity that may arise at the wall, it has been taken care of by specifying same inlet velocity at the wall as the wall velocity. In any case it should not be a problem as eventually this wall velocity would be calculated as a solution.
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