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Getting different results when applying fixed pressure/flow rate initial conditions

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Old   October 11, 2019, 18:18
Default Getting different results when applying fixed pressure/flow rate initial conditions
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Yanxuan Shao
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Hi,

I am trying to simulate flow in a 2-D pipe with obstacles using SimpleFoam solver (laminar). I used both fixed inlet/outlet pressure and fixed flow rate of the pipe for initial condition. The two situations have similar Re (which is around 20000), while their results are very different in the section of pipe without obstacles after the turbulence is fully developed. Attached are pictures of results of the two simulation (1. results with fixed pressure initial condition, 2. results with fixed flow rate initial condition). So I am wondering which one of the results (or maybe neither of them) is correct, and what causes this. Thank you so much for your reply in advance!

Best,
Charlotte
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Old   October 17, 2019, 01:30
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Ruiyan Chen
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Have you compared the flow rate in both cases? Are they the same?

I don't think fixed inlet/outlet pressure is a good pair, it doesn't make sense at least in my opinion. Also, in terms of the velocity contour from the first picture, why the velocity is not uniform at the inlet (assuming that the flow goes from left to right)?

For pipe flows common practice would be velocity-inlet and pressure-outlet, and you can assign a velocity profile at the inlet to make it more realistic.
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Old   October 17, 2019, 09:33
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Yanxuan Shao
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Hi Ruiyan,

Thanks for your reply. Yes I checked both flow rate and they are the same.

For the first one, I guess velocity is not uniform because only inlet pressure is controlled.

I will try velocity inlet and pressure outlet as you suggested. Thanks!

Charlotte
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