Absolute or relative pressures in cavitatingFoam

d.lagattolla · February 10, 2015, 14:21

Hi guys! A simple question..I 'd like to know if the pressure values in the "p" file in the 0 folder for cavitatingFoam are absolute or relative pressures.

Thank you in advance!

D_LEE · February 11, 2015, 12:14

I think that it is absolute pressure because in the solver there is no mention of atmospheric pressure.

That being said this is only going to change your answer by 1% as the low pressure boundary is 100e+05 Pa.

d.lagattolla · February 11, 2015, 13:29

Ok thank you!

d.lagattolla · February 13, 2015, 12:38

Hey D_LEE I haven't quite understood yor second sentence.. what do you mean by "the low pressure boundary" being that value you said? What pressure are you referring to? Sorry i am totally new to OpenFOAM and there are a lot of things I don't know.
Thank you again for answering!

D_LEE · February 13, 2015, 12:59

In the throttle case, if you go to the 0/ directory you will see the boundary conditions for each field set for your case.

The pressure boundary condition is in p, and form there you can see that the boundary conditions of pressure force your fluid through the gap, the high pressure inlet is:

inlet
{
type totalPressure;
U U;
phi phiv;
rho rho;
psi none;
gamma 1;
p0 uniform 300e5;
}

and the low pressure outlet is:

outlet
{
type fixedValue;
value uniform 100e5;
}

both are units of Pa:

dimensions [1 -1 -2 0 0];

So when you are asking about the pressure being absolute or gauge pressure, its just going to change the boundaries by 1e5 Pa anyway so it probably wouldn't matter.

d.lagattolla · February 13, 2015, 13:12

Ok i didn't realize you were talking about the tutorial specifically. Thank you very much!

February 10, 2015, 14:21	Absolute or relative pressures in cavitatingFoam	#1
d.lagattolla New Member Join Date: Feb 2015 Posts: 7 Rep Power: 11	Hi guys! A simple question..I 'd like to know if the pressure values in the "p" file in the 0 folder for cavitatingFoam are absolute or relative pressures. Thank you in advance! Last edited by d.lagattolla; February 11, 2015 at 13:30.

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February 11, 2015, 12:14		#2
D_LEE New Member Damon Lee Join Date: Sep 2014 Posts: 16 Rep Power: 12	I think that it is absolute pressure because in the solver there is no mention of atmospheric pressure. That being said this is only going to change your answer by 1% as the low pressure boundary is 100e+05 Pa.

February 11, 2015, 13:29		#3
d.lagattolla New Member Join Date: Feb 2015 Posts: 7 Rep Power: 11	Ok thank you!

February 13, 2015, 12:38		#4
d.lagattolla New Member Join Date: Feb 2015 Posts: 7 Rep Power: 11	Hey D_LEE I haven't quite understood yor second sentence.. what do you mean by "the low pressure boundary" being that value you said? What pressure are you referring to? Sorry i am totally new to OpenFOAM and there are a lot of things I don't know. Thank you again for answering!

February 13, 2015, 12:59		#5
D_LEE New Member Damon Lee Join Date: Sep 2014 Posts: 16 Rep Power: 12	In the throttle case, if you go to the 0/ directory you will see the boundary conditions for each field set for your case. The pressure boundary condition is in p, and form there you can see that the boundary conditions of pressure force your fluid through the gap, the high pressure inlet is: inlet { type totalPressure; U U; phi phiv; rho rho; psi none; gamma 1; p0 uniform 300e5; } and the low pressure outlet is: outlet { type fixedValue; value uniform 100e5; } both are units of Pa: dimensions [1 -1 -2 0 0]; So when you are asking about the pressure being absolute or gauge pressure, its just going to change the boundaries by 1e5 Pa anyway so it probably wouldn't matter.

February 13, 2015, 13:12		#6
d.lagattolla New Member Join Date: Feb 2015 Posts: 7 Rep Power: 11	Ok i didn't realize you were talking about the tutorial specifically. Thank you very much!