# BuoyantBoussinesq(Pimple/Piso)Foam, changed equation from OF 1.6 to 1.7 ???

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 September 27, 2010, 10:37 BuoyantBoussinesq(Pimple/Piso)Foam, changed equation from OF 1.6 to 1.7 ??? #1 New Member   Jan Join Date: Jun 2010 Location: Erlangen, Germany Posts: 3 Rep Power: 7 Hi Folks, one question regarding the changes from OF 1.6 to 1.7 in the buoyantBoussinesq(Piso/Pimple)Foam solver. I think the implementation of splitting the pressure according to p = p_rgh + rho*g.x is not fully correct. The pressure equation in OF 1.7 seems OK, since in the Rhie-Chow formulation the contributions from the static pressure cancel and we are left with: Code: phi = (fvc::interpolate(U) & mesh.Sf()) + fvc::ddtPhiCorr(rUA, U, phi); surfaceScalarField buoyancyPhi = rUAf*ghf*fvc::snGrad(rhok)*mesh.magSf(); phi -= buoyancyPhi; instead of Code: surfaceScalarField phiU ( (fvc::interpolate(U) & mesh.Sf()) + fvc::ddtPhiCorr(rUA, U, phi) ); phi = phiU + rUAf*fvc::interpolate(rhok)*(g & mesh.Sf()); in OF 1.6. In contrast, in the momentum equation the term for the buoyancy ( and gravity) force has changed from (OF 1.6) Code: fvc::reconstruct( ... fvc::interpolate(rhok)*(g & mesh.Sf()) ...) to (OF 1.7) Code: fvc::reconstruct( ... - ghf*fvc::snGrad(rhok)*mesh.magSf() ...) These are two different expressions: F ~ rhok * g vs. F ~ gradT * g.h Is this really a bug or do I miss some point? Thanks for any comment... Regards, Jan Edit: In the meantime I am pretty sure this is indeed a bug and I submitted a bugreport. Edit: Problem is solved. This bug was fixed a few days ago in the git repository. Last edited by myself; October 7, 2010 at 11:19.

 July 28, 2011, 05:21 #2 Senior Member   Anne Gerdes Join Date: Aug 2010 Location: Hamburg Posts: 152 Rep Power: 7 Dear Foamers, can someone explain me why OF1.7 still uses HTML Code: - ghf*fvc::snGrad(rhok)*mesh.magSf() instead of HTML Code: fvc::interpolate(rhok)*(g & mesh.Sf()) as it was used in the previous version OF1.6. I do not understand why the gradient of the densitiy is used while in the equations I find in literature it has to be just the densitiy multiplied with the constant g. Can someone help me? Is this still a bug or do I overlook something?

 September 13, 2011, 08:38 #3 Senior Member   Anne Gerdes Join Date: Aug 2010 Location: Hamburg Posts: 152 Rep Power: 7 For the answer see Problems in understanding BuoyantBoussinesqSimpleFoam

September 14, 2011, 02:03
#4
Senior Member

Dr. Alexander Vakhrushev
Join Date: Mar 2009
Posts: 213
Rep Power: 10
Quote:
 Originally Posted by myself Hi Folks, one question regarding the changes from OF 1.6 to 1.7 in the buoyantBoussinesq(Piso/Pimple)Foam solver. I think the implementation of splitting the pressure according to p = p_rgh + rho*g.x is not fully correct. The pressure equation in OF 1.7 seems OK, since in the Rhie-Chow formulation the contributions from the static pressure cancel and we are left with: Code: phi = (fvc::interpolate(U) & mesh.Sf()) + fvc::ddtPhiCorr(rUA, U, phi); surfaceScalarField buoyancyPhi = rUAf*ghf*fvc::snGrad(rhok)*mesh.magSf(); phi -= buoyancyPhi; instead of Code: surfaceScalarField phiU ( (fvc::interpolate(U) & mesh.Sf()) + fvc::ddtPhiCorr(rUA, U, phi) ); phi = phiU + rUAf*fvc::interpolate(rhok)*(g & mesh.Sf()); in OF 1.6. In contrast, in the momentum equation the term for the buoyancy ( and gravity) force has changed from (OF 1.6) Code: fvc::reconstruct( ... fvc::interpolate(rhok)*(g & mesh.Sf()) ...) to (OF 1.7) Code: fvc::reconstruct( ... - ghf*fvc::snGrad(rhok)*mesh.magSf() ...) These are two different expressions: F ~ rhok * g vs. F ~ gradT * g.h Is this really a bug or do I miss some point? Thanks for any comment... Regards, Jan Edit: In the meantime I am pretty sure this is indeed a bug and I submitted a bugreport. Edit: Problem is solved. This bug was fixed a few days ago in the git repository.
Hallo Jan!

You wrote that the term in OF17 was formulated with an error, am I correct?

But still if i look OF171 (Ubuntu package installed via apt-get):

Code:
UEqn
==
fvc::reconstruct
(
(
)*mesh.magSf()
)
Is this term still there? And how it should be?

Regards,
Alexander
__________________
Best regards,

Dr. Alexander VAKHRUSHEV

Christian Doppler Laboratory for "Advanced Process Simulation of
Solidification and Melting"

Simulation and Modelling of Metallurgical Processes
Department of Metallurgy
University of Leoben

Franz-Josef-Str. 18
A - 8700 Leoben
Österreich / Austria
Tel.: +43 3842 - 402 - 3125
http://smmp.unileoben.ac.at

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