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Unexpected results from interFoam

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Old   February 23, 2010, 17:39
Default Unexpected results from interFoam
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I am running the interFoam solver to do what I hoped would be a simple mulitphase simulation: filling a one-dimensional column with a mixture of water and air (without gravity).

When I run the simulation with the input liquid volume fraction equal to one, I get results that I expect (see filling tube plot).

However, when I changed the volume fraction to 0.75, I get weird oscillations in the liquid volume fraction as a function of height (see weird plot). I have tried changing the cell size and time steps, but I still had similar problems.

Boundary conditions:

Top of column (RHS in plots):
pressure = 1 atm
velocity -> zeroGradient
liquid volume fraction -> zeroGradient

Bottom of column (LHS in plots):
pressure -> zeroGradient
velocity = 10 cm/s
liquid volume fraction = {1 seems to work fine, <1 does not}

Initial conditions:
pressure = 1 atm
velocity = zero
liquid volume fraction = 0

I would like to understand what I am doing wrong and to hopefully get some help on how to get it right. Please let me know if any more information is needed.

Thanks,
Mike
Attached Files
File Type: pdf filling_tube.pdf (2.1 KB, 37 views)
File Type: pdf weird.pdf (3.7 KB, 31 views)
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Old   March 30, 2011, 22:31
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Dave West
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Mike -
I'm no expert on VOF methods, but my understanding is that it is looking for the interface between 2 fluids that don't mix. If you put in a fluid that is a uniform 75% phase 1 (and 25% phase 2), they are mixed to the sub-grid scale, and the code can't find a surface to separate them on. I wouldn't expect a good answer. If you bring in some of each phase, at 100% and 0%, separated to the scale of the mesh, I expect you would see better results.

Terp
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Old   March 31, 2011, 11:05
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Terp,

Thanks for the reply. I need to understand the tools before I know what I can do with them

Mike
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