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Why should we define both P and U for boundaries? |
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October 17, 2010, 22:50 |
Why should we define both P and U for boundaries?
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#1 |
Senior Member
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Dear Foamers,
What should be velocity boundary condition (U) type for outlet of a problem which we want set pressure (P) as fixedValue. We can't suppose it zeroGradient because it is not fully developed at outlet. and i don't know why should we define both of P and U for boundaries in OpenFOAM. |
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October 18, 2010, 03:20 |
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#2 |
Senior Member
Christian Lucas
Join Date: Aug 2009
Location: Braunschweig, Germany
Posts: 202
Rep Power: 17 |
Hi,
you have to define BC for each field you are solving, so you need a BC for U and p. Other CFD software like fluent or cfx does the same (without telling you). zeroGradients is the correct BC (or better inletOutlet) for U at the outlet. Of course your BC has an effect on the solution (as in all CFD software), so you must place the outlet BC far (at least a bit) away from the area of interest. Regards, Christian |
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October 18, 2010, 03:55 |
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#3 | |
Senior Member
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Quote:
the problem is in processing algorithm depend on its form, in boundary cell we set pressure and the algorithm try to calculate a velocity which satisfy continuity and ... so setting both of U and P leads to have more equations than unknowns and this is the cause that other softwares like Fluent don't need to define both of them. |
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