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I don't see a problem with the bubbleColumn, could you be more specific about which bubbleColumn case and at what time you see what level of extreme non zero-velocities? |
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Sorry, I didn't mean there are extreme velocities in the bubbleColumn test case (laminar one) but only non zero-velocities in the region occupied by air where the water fraction is zero (see picture attached). The extreme values are found in my test case where, of course, they might be due to issues with the setup but I'm wondering if this is the correct behavior of the solver. pic.png (199,783 bytes) |
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Why should the water velocity be zero where the water fraction is zero? Formally it is unknown but in the simulations it will approach the velocity of the continuous phase as the phase-fraction -> 0 due to the drag. |
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Multiphase flows are not my main field of expertise, but I was guessing there can't be, physically, any velocity associated with one phase which is not present at that particular location (i.e. the phase/volume fraction is zero). |
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It is not possible to define the velocity of something that isn't there, zero or otherwise. |
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Ok, but wouldn't be zero-padding in cells where the volume fraction is zero within a given threshold be a better option to avoid velocity values higher than physical ones (as in the air region of the picture above where maximum water velocity is about 0.5 where there is no water while the actual maximum value is about 0.3 where the volume fraction is not zero) and relax the Co constraint or would this lead to numerical/stability issues? |
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If you need the phase velocity to be exactly zero when the phase-fraction is zero you will need to add a damping model to do this. e.g. via an fvOption. |
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User support request. |
- Anonymous
