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icoFoam pressures for solid-fluid coupled system

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Old   October 1, 2018, 22:57
Default icoFoam pressures for solid-fluid coupled system
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Kahlil Fredrick Cui
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I am simulating particle flow in a fluid domain. The particles move in cyclic boundaries while the fluid is stationary and merely reacts to the particle motion (the image of the system is attached below). The fluid part is solved using icoFoam. I set the fluid BCs at both left, right and top walls as totalPressure for pressure and pressureInletOutletVelocity for velocity because I want the fluid to come in and out of the domain freely.

The problem is this, when I set the fluid domain boundaries exactly at the same size as the particle boundaries I get a strong positive pressure in the left (in) and a negative pressure at the right (out). But when I extend the flow-wise boundaries a little bit, the positive pressure disappears and now I have two negative pressures at both ends. I have attached the images of the pressures below.

I am thinking its a numerical effect, but I still cannot wrap my head about how pressures are discretized and solved. Personally, I find the positive pressures to be abnormal but I also cannot find any reason why negative pressures will develop at both ends and not only on one. Or maybe my BCs are wrong altogether.

I would really appreciate any ideas and advice you can give me (I'm kinda running desperate already). Thanks in advance!
Attached Images
File Type: jpg system3.jpg (43.6 KB, 8 views)
File Type: png no_excess.png (153.4 KB, 8 views)
File Type: png excess.png (146.5 KB, 9 views)
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