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September 27, 2011, 12:46 
Pressure definition in OF 2.0.1 (simpleFoam etc.)

#1 
Member
Miles
Join Date: Sep 2011
Posts: 48
Rep Power: 7 
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 Pstaticrho*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/rhog*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 

September 28, 2011, 15:25 

#2  
Senior Member
Daniel P. Combest
Join Date: Mar 2009
Location: St. Louis, USA
Posts: 612
Rep Power: 22 
Quote:
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 

September 28, 2011, 17:16 

#3 
Senior Member
Vesselin Krastev
Join Date: Jan 2010
Location: University of Tor Vergata, Rome
Posts: 364
Rep Power: 12 
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 prho*g*h.
Hope this helps V. 

September 29, 2011, 18:35 

#4 
Member
Miles
Join Date: Sep 2011
Posts: 48
Rep Power: 7 
thanks for your replies
regards miles 

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