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interFoam, nonuniform alpha for channel flow

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Old   February 23, 2017, 22:41
Default interFoam, nonuniform alpha for channel flow
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KTG
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Hi Foamers,

I am trying to setup a simple test case for channel flow boundary conditions. I would like to have river-like flow, using the interFoam solver. The attached zip contains a case file, where water is invading a square channel, and displacing air (see screenshot). I have two questions:

1) Is there a simple way to set the value of alpha at the boundary to be noninform in space? For example, alpha=1 for y<=.5, alpha=0 for y>.5. This is just a shifted heavyside function of y, but I can't figure out how to implement it. I will eventually be using these boundary conditions with a more complicated geometry, so my goal is to find a way to implement different water heights without having to re-mesh every time. This seems simple enough that I shouldn't have to write a new boundary condition, but I am lost on the implementation. Its ok if the water height is constant in time.

2) In the attached case, I have set pressure and velocity boundary conditions based on what I have read on the forums for stability reasons. In reality, I have measured the velocity, but not the pressure in a river. Why is it ok to set uniform pressures at the boundaries , and how should I choose the actual values? Also, it seems that things are not stable unless I put a little water against the inlet for the initial value. This is not really a problem, but if someone can explain that behavior, I would be very interested.

Thanks!
Attached Images
File Type: jpg channel_flow.jpg (23.1 KB, 40 views)
Attached Files
File Type: zip square_channel.zip (7.9 KB, 19 views)
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