Pressure equation & icoFoam

sasanghomi · June 19, 2013, 15:56

Hi Foamers,

I have a question about pressure equation in icoFoam . we know pressure equation in icoFoam is as below : (according to Prof.jasak's thesis)
$\triangledown .(\frac{1}{a_{p}}\triangledown p)=\triangledown .\frac{H(u)}{a_{p}}$

In the source code we have :

Code:

 fvm::laplacian(rUA, p) == fvc::div(phi)

I don't understand how div(phi) ensures below term in the pressure equation !
$\triangledown .\frac{H(u)}{a_{p}}$
what is the relation between this term and divergence of flux (phi) ?

I appreciate any help from you,
Thanks and best regards,
Sasan.

Cyp · June 20, 2013, 03:47

Hi Sasam,

it is just a programing trick that has disappear in the latest OF version.

see http://www.cfd-online.com/Forums/ope...ning-hbya.html for additional informations.

Best,
Cyp

sasanghomi · June 20, 2013, 04:00

Hi Cyprien ,

Thanks for your reply But I didn't find my answer in meaning of HbyA .
I think the pressure term should drop for getting this relation.
Can you explain more ? about this trick ?

Thanks and best regards,
Sasan.

Cyp · June 20, 2013, 04:06

what I mean is that

$\nabla .\frac{H(u)}{a_{p}}= \nabla . \phi$

but in reality, in this equation $\phi$ does not represent the velocity field. $\phi$ is overwritten just after the calculation of p to obtain the corrected velocity flux field.

sasanghomi · June 20, 2013, 04:21

I got it , thank you very much.

sharonyue · July 16, 2013, 04:17

Quote:

Originally Posted by Cyp

what I mean is that

$\nabla .\frac{H(u)}{a_{p}}= \nabla . \phi$

but in reality, in this equation $\phi$ does not represent the velocity field. $\phi$ is overwritten just after the calculation of p to obtain the corrected velocity flux field.

Hi Cyp,

$\nabla .\frac{H(u)}{a_{p}}= \nabla . \phi$
Im confused about this, I think divergence of a scalar equals zero. Can you explain more?
Thanks

June 19, 2013, 15:56	Pressure equation & icoFoam	#1
sasanghomi Senior Member Sasan Ghomi Join Date: Sep 2012 Location: Denmark Posts: 292 Rep Power: 14	Hi Foamers, I have a question about pressure equation in icoFoam . we know pressure equation in icoFoam is as below : (according to Prof.jasak's thesis) $\triangledown .(\frac{1}{a_{p}}\triangledown p)=\triangledown .\frac{H(u)}{a_{p}}$ In the source code we have : Code: fvm::laplacian(rUA, p) == fvc::div(phi) I don't understand how div(phi) ensures below term in the pressure equation ! $\triangledown .\frac{H(u)}{a_{p}}$ what is the relation between this term and divergence of flux (phi) ? I appreciate any help from you, Thanks and best regards, Sasan.

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June 20, 2013, 03:47		#2
Cyp Senior Member Cyprien Join Date: Feb 2010 Location: Stanford University Posts: 299 Rep Power: 18	Hi Sasam, it is just a programing trick that has disappear in the latest OF version. see http://www.cfd-online.com/Forums/ope...ning-hbya.html for additional informations. Best, Cyp

June 20, 2013, 04:00		#3
sasanghomi Senior Member Sasan Ghomi Join Date: Sep 2012 Location: Denmark Posts: 292 Rep Power: 14	Hi Cyprien , Thanks for your reply But I didn't find my answer in meaning of HbyA . I think the pressure term should drop for getting this relation. Can you explain more ? about this trick ? Thanks and best regards, Sasan.

June 20, 2013, 04:06		#4
Cyp Senior Member Cyprien Join Date: Feb 2010 Location: Stanford University Posts: 299 Rep Power: 18	what I mean is that $\nabla .\frac{H(u)}{a_{p}}= \nabla . \phi$ but in reality, in this equation $\phi$ does not represent the velocity field. $\phi$ is overwritten just after the calculation of p to obtain the corrected velocity flux field.

June 20, 2013, 04:21		#5
sasanghomi Senior Member Sasan Ghomi Join Date: Sep 2012 Location: Denmark Posts: 292 Rep Power: 14	I got it , thank you very much.