# basic question

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 April 6, 2010, 13:47 basic question #1 Member   Axel Söhngen Join Date: Jan 2010 Location: Germany, Trier Posts: 31 Rep Power: 7 Hello, can anybody say me what output of pressure OpenFoam delivers? For example when I simulate a flow in side a pipe is the pressure in the pipe only the change of pressure or the change of pressure + atmospheric pressure or something else? Thank you

 April 6, 2010, 17:15 #2 Senior Member   Vesselin Krastev Join Date: Jan 2010 Location: University of Tor Vergata, Rome Posts: 361 Rep Power: 10 It depends of what kind of solver are you using. If it is an incompressible flow solver, the pressure output is the kinematic (p/rho) relative pressure, measured from an initial arbitrary reference value (which is not relevant for the flow solution). If it is a compressible one, the pressure output is the absolute effective pressure (p) in your domain, which has much more importance for your solution.

 April 7, 2010, 04:21 #3 Member   Axel Söhngen Join Date: Jan 2010 Location: Germany, Trier Posts: 31 Rep Power: 7 Ok thank you that helps me!

April 7, 2010, 09:06
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Cean
Join Date: Feb 2010
Posts: 128
Rep Power: 7
Quote:
 Originally Posted by vkrastev If it is an incompressible flow solver, the pressure output is the kinematic (p/rho) relative pressure, measured from an initial arbitrary reference value (which is not relevant for the flow solution).
I am trying to understand the p/rho output for potentialFoam cylinder sample. How could I get the relevent pressure field?

Thanks

Cean

 April 7, 2010, 13:43 #5 Member   Axel Söhngen Join Date: Jan 2010 Location: Germany, Trier Posts: 31 Rep Power: 7 So is the pressure = p(reference) - p ?

 April 8, 2010, 04:53 #6 Senior Member   Vesselin Krastev Join Date: Jan 2010 Location: University of Tor Vergata, Rome Posts: 361 Rep Power: 10 For the incompressible solvers the p/rho output is a difference between the calculated and the reference value: so, if the reference value is set to zero, an output of 10 means +10 m^2/s^2 measured from the reference and so on (for example, you can imagine that the zero value corresponds to the atmospheric p/rho value in standard conditions and then evaluate the effective pressure in your domain at the end of the calculations). For the incompressible solvers you are forced to set realistic initial values of effective absolute pressure and temperature, because both of them influence the initial density (rho) value of the species contained in your domain. At the end of the calculation, the pressure output is exactly the absolute pressure (p, measured in Pa) in your domain. Regards

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