pressure in interFoam

idefix · August 8, 2015, 14:23

Hello together,

I am confused at the moment.
iinterFoam writes a p and a p_rgh - file in the time-folder.
What is p?
Total pressure or static pressure?
How can I calculate the total pressure?

Thanks for your help

ssss · August 8, 2015, 18:14

p is the static pressure.

In interfoam:

$p_{rgh}= p-\rho\vec{g} \cdot \vec{h}$

In non-multiphase incompressible solvers:

$p_{rgh}= \frac{p}{\rho}-\vec{g} \cdot \vec{h}$

idefix · August 9, 2015, 01:13

Thanks for your explanation.

But are you sure that p is divided by the density?
The dimension given in the p-file are:
dimensions [1 -1 -2 0 0 0 0]

ssss · August 9, 2015, 01:32

Yes you are right, I was thinking about simpleFoam and other solvers I will edit my post

tareqkh · August 9, 2015, 01:52

I have quick question about simpleFoam. I have made a mesh that fits an inviscid case, but the issue how can I use simpleFoam as an inviscid solver. Have you guys used simpleFoam before?

Thanks in advance,

Tareq

idefix · August 9, 2015, 03:23

Quote:

Originally Posted by ssss

p is the static pressure.
p_rgh is p-vec(g) dot (h)

As far as I understood it should be
p_rgh = p-vec(g) dot (h) dot (rho)

Am I right, that I can calculate the total pressure in the following way:

p_tot = p + 0.5 * (mag(U))^2 rho ?

idefix · August 9, 2015, 03:25

Quote:

Originally Posted by tareqkh

I have quick question about simpleFoam. I have made a mesh that fits an inviscid case, but the issue how can I use simpleFoam as an inviscid solver. Have you guys used simpleFoam before?

Thanks in advance,

Tareq

It would be a kind of "cheating" but setting the viscosity in the transportProperties-file to a very small value?

tareqkh · August 9, 2015, 03:31

Hello,

Thank you for you kind response. I have tried to set up the viscosity almost to zero, but I am not getting a good convergence history. Any idea...? Sorry to bring this question to your question that you are already asked.

Best,

Tareq

idefix · August 9, 2015, 04:25

do you have a good convergence when you use viscosity (much greater than zero)?

tareqkh · August 9, 2015, 04:27

Good question. No, I have not obtained a good convergence history in both cases.

Best,

Tareq

idefix · August 9, 2015, 04:29

maybe check your boundary condition first and then turn off the viscosity

tareqkh · August 9, 2015, 05:22

I am using boundary conditions that I used in one of my old cases since I obtained excellent results. So, I don't think that the problem of is from boundary conditions.

Best,

Tareq

idefix · August 9, 2015, 07:30

and where is the difference between the old and new case (if not the boundary conditions)?

tareqkh · August 9, 2015, 22:37

Here are pictures from the mesh and convergence history for the inviscid case. I am guessing this might be the problem.

August 8, 2015, 14:23	pressure in interFoam	#1
idefix Member Join Date: Aug 2011 Posts: 89 Rep Power: 14	Hello together, I am confused at the moment. iinterFoam writes a p and a p_rgh - file in the time-folder. What is p? Total pressure or static pressure? How can I calculate the total pressure? Thanks for your help Last edited by idefix; August 8, 2015 at 15:55.

August 8, 2015, 18:14		#2
ssss Senior Member anonymous Join Date: Aug 2014 Posts: 205 Rep Power: 12	p is the static pressure. In interfoam: $p_{rgh}= p-\rho\vec{g} \cdot \vec{h}$ In non-multiphase incompressible solvers: $p_{rgh}= \frac{p}{\rho}-\vec{g} \cdot \vec{h}$ miotto likes this. Last edited by ssss; August 9, 2015 at 04:45.

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August 9, 2015, 01:13		#3
idefix Member Join Date: Aug 2011 Posts: 89 Rep Power: 14	Thanks for your explanation. But are you sure that p is divided by the density? The dimension given in the p-file are: dimensions [1 -1 -2 0 0 0 0]

August 9, 2015, 01:32		#4
ssss Senior Member anonymous Join Date: Aug 2014 Posts: 205 Rep Power: 12	Yes you are right, I was thinking about simpleFoam and other solvers I will edit my post

August 9, 2015, 01:52		#5
tareqkh Senior Member CFD Join Date: Nov 2010 Location: United States Posts: 243 Rep Power: 16	I have quick question about simpleFoam. I have made a mesh that fits an inviscid case, but the issue how can I use simpleFoam as an inviscid solver. Have you guys used simpleFoam before? Thanks in advance, Tareq

August 9, 2015, 03:31		#8
tareqkh Senior Member CFD Join Date: Nov 2010 Location: United States Posts: 243 Rep Power: 16	Hello, Thank you for you kind response. I have tried to set up the viscosity almost to zero, but I am not getting a good convergence history. Any idea...? Sorry to bring this question to your question that you are already asked. Best, Tareq

August 9, 2015, 04:25		#9
idefix Member Join Date: Aug 2011 Posts: 89 Rep Power: 14	do you have a good convergence when you use viscosity (much greater than zero)?

August 9, 2015, 04:27		#10
tareqkh Senior Member CFD Join Date: Nov 2010 Location: United States Posts: 243 Rep Power: 16	Good question. No, I have not obtained a good convergence history in both cases. Best, Tareq

August 9, 2015, 04:29		#11
idefix Member Join Date: Aug 2011 Posts: 89 Rep Power: 14	maybe check your boundary condition first and then turn off the viscosity

August 9, 2015, 05:22		#12
tareqkh Senior Member CFD Join Date: Nov 2010 Location: United States Posts: 243 Rep Power: 16	I am using boundary conditions that I used in one of my old cases since I obtained excellent results. So, I don't think that the problem of is from boundary conditions. Best, Tareq

August 9, 2015, 07:30		#13
idefix Member Join Date: Aug 2011 Posts: 89 Rep Power: 14	and where is the difference between the old and new case (if not the boundary conditions)?