Periodic BC for VOF

ragh80 · June 23, 2010, 03:34

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.

Oxmox · June 23, 2010, 07:32

Hi,
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...

ragh80 · June 23, 2010, 16:04

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.

June 23, 2010, 03:34	Periodic BC for VOF	#1
ragh80 New Member Raghvendra Gupta Join Date: Mar 2009 Posts: 2 Rep Power: 0	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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June 23, 2010, 07:32		#2
Oxmox New Member Join Date: Jun 2010 Posts: 11 Rep Power: 15	Hi, 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...

June 23, 2010, 16:04		#3
ragh80 New Member Raghvendra Gupta Join Date: Mar 2009 Posts: 2 Rep Power: 0	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.