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-   -   About internalField p in OpenFOAM (http://www.cfd-online.com/Forums/openfoam/109733-about-internalfield-p-openfoam.html)

sharonyue November 25, 2012 05:28

About internalField p in OpenFOAM
 
Hi Foamers:



I see the internalField of p and p_rhg is uniform 0 in many cases, and I change "0" to any value such as "5000","10000", the result is the same. you can try it in damBreak case.the different value of internalfield p has totally no compact to the result. I dont know why. I would be appreciated if you can give me some hints.

Horus November 25, 2012 11:57

This is true for incompressible solvers. Changing the pressure has no effect on the result but a pressure higher by the some amount everywhere.

From http://www.cfd-online.com/Wiki/Incompressible_flow
Quote:

A consequence of incompressible flow is that there is no equation of state for pressure, unlike in compressible flow. Since there is no separate equation for pressure, it must be obtained from the continuity and momentum equations. The main role of pressure is to satisfy the zero divergence condition of the velocity field. Note that pressure is only determined up to a constant.
Additionally OpenFOAM does not use physical pressure in this case but p_OF = p/rho (afaik for reasons of machine precision).

Regards,
Florian

sharonyue November 25, 2012 20:06

Quote:

Originally Posted by Horus (Post 394061)
This is true for incompressible solvers. Changing the pressure has no effect on the result but a pressure higher by the some amount everywhere.

The main role of pressure is to satisfy the zero divergence condition of the velocity field. Note that pressure is only determined up to a constant.

Thanks Florian, but regarding to damBreak case, I set the internalField of p_rgh is "5000" instead of "0", the result dont show a raise of p as a whole. neither of p_rgh.

In that wikki, it surely makes sense, but I think , does this problem be ralated to the PISO or SIMPLE algorithm?

sharonyue November 26, 2012 03:16

Quote:

Originally Posted by namld094nh (Post 394104)
c?m on vi th├┤ng tin b? ├*ch........................

um.....thats Mars language? jk...:D


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