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-   -   Pressure definition in OF 2.0.1 (simpleFoam etc.) (https://www.cfd-online.com/Forums/openfoam/92861-pressure-definition-2-0-1-simplefoam-etc.html)

 miles_davis September 27, 2011 12:46

Pressure definition in OF 2.0.1 (simpleFoam etc.)

Hi,
Does anyone know what is pressure in OF2.0.1 for solver like SimpleFOAM?

I have read that in previous versions of the code it was in fact Pstatic-rho*g*h, than in another version it was just Pstatic/rho. What is the actual statement for OF 2.0.1?

The source of my question is simple: Consider a water box. you model inlet and outlet.
If the outlet is at the bottom (i.e.altitude is lower than the inlet) what BC do I define for pressure at the outlet???
If P stands for p/rho, I have to calculate the hydrostatic pressure at he bottom.
If p stands fo p/rho-g*h: I just have to put P=0.

Thanks for you help.

Regards,

Miles

P.S;: I have found post on the subject but it was for older version as OF 1.7

 chegdan September 28, 2011 15:25

Quote:
 Originally Posted by miles_davis (Post 325814) Hi, Does anyone know what is pressure in OF2.0.1 for solver like SimpleFOAM? I have read that in previous versions of the code it was in fact Pstatic-rho*g*h, than in another version it was just Pstatic/rho. What is the actual statement for OF 2.0.1? The source of my question is simple: Consider a water box. you model inlet and outlet. If the outlet is at the bottom (i.e.altitude is lower than the inlet) what BC do I define for pressure at the outlet??? If P stands for p/rho, I have to calculate the hydrostatic pressure at he bottom. If p stands fo p/rho-g*h: I just have to put P=0. Thanks for you help. Regards, Miles P.S;: I have found post on the subject but it was for older version as OF 1.7
Miles,

For simpleFoam it is a relative pressure related to a reference value. If you look at the creatFields.H and Peqn.H in the simpleFoam solver that might help.

Dan

 vkrastev September 28, 2011 17:16

You are confusing compressible and incompressible solvers. As far as I know, all the incompressible solvers in OF (like simpleFoam or pisoFoam), in all the releases (at least from the 1.6 to the 2.0.1, including the -dev/-ext ones), solve for the kinematic relative pressure, i. e. for p/rho (if rho is a constant, defining the pressure source term in the momentum equation as -1/rho*grad(p) or as -grad(p/rho) is equivalent). For the compressible solvers, things are not so established between different releases (honestly i really can't understand why), as for example in the 1.6 release a solver like rhoSimpleFoam assumes the static pressure as the dependent variable, while in the 1.7.0/1/x (and I think also in the 2.0.0/1/x family) the dependent variable is p-rho*g*h.

Hope this helps

V.

 miles_davis September 29, 2011 18:35