Need Help w. Darcy Boussinesq Equ.

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 October 12, 2011, 14:26 #21 Senior Member   Cyprien Join Date: Feb 2010 Location: Stanford University Posts: 245 Rep Power: 10 Try to impose a delta P (fixedValue for inlet and fixedValue = 0 for outlet). If you want a immobile system, I think a zeroGradient for inlet and fixedValue = 0 for outlet should work... Note that since we solve only the pressure and the temperature in the solver, the boundary condition for the velocity field are not accounted for.

 October 12, 2011, 15:33 #22 New Member   Werner Join Date: Dec 2009 Location: Austria Posts: 13 Rep Power: 8 The problem we try to solve is this onset of thermal convection in a porous cylinder with conducting wall. So there is no inlet or outlet. I also thougt that there is maybe a problem with the boundaries. In most cases when i got a floiting point exception, it was a problem with the bopundaries. But the mainproblem is (i think), that the pressureequation is not properly solved or coded. Cheers

October 12, 2011, 23:22
#23
New Member

Tom
Join Date: Sep 2011
Posts: 11
Rep Power: 7
Gday Cyp and Nep

Thanks so much for your input and collaboration, this has been a huge help to me.

I re-wrote my solver, based on the laplacianFoam. I wrote up some comments along the way.

I'd like to look into it to 'see' how pressure and velocity are linked. That is what I will do next, to make sure its working as expected at this stage.

I'm going to try to set up a pressure gradient with the boundary conditions as you two were discussing.

my method is
break the problem into a number of smaller steps on Cyps guidance
1. solve simple Darcy's Law, based on laplacianFoam (exclude the Temp term)
2. include a scalar transport equation
3. then look at adding temperature
4. then look at correcting T,U
5. add the (Ra*T*k) term to the U eqn
Cheers

Tom
Attached Files
 darcyLaplacianFoam.C (2.4 KB, 20 views) README.txt (3.8 KB, 14 views)

 October 13, 2011, 09:25 #24 New Member   Werner Join Date: Dec 2009 Location: Austria Posts: 13 Rep Power: 8 Hi Tom, wich equation you want to solve? Is it necessary to handle the equations in a dimensionless form. What i try to say is, that MAYBE (im no Pro in Openfoam) it is not so easy to handle nondimensionless equations in Openfoam. Btw how is it going on?? Cheers Werner

October 13, 2011, 09:52
#25
New Member

Tom
Join Date: Sep 2011
Posts: 11
Rep Power: 7
Hi Werner

Im solving for convection in a box of porous media. Sounds very similar to your problem otherwise. I do want to do it in terms of the Rayleigh number and non-dimensional temperature.

I will fudge the units if i have to ! it seems to work ok with the dimensions switched off in the /opt location. I just dont like fiddling with those settings bcoz im an amatuer.

At the moment, i am trying to make the darcyLaplacian solver with some temperature terms added. I seem to be missing a curly bracket, but I'm not sure where.

Did you get a pressure gradient working?

Cheers

Tom
edit

I added my solver and the TEqn it needs. Im having issues now with boundaryConditions. It doesnt like taking the gradient of a calculated internalField.
Attached Files
 laplacianFoam.C (2.4 KB, 11 views) TEqn.H (181 Bytes, 11 views)

Last edited by TomB; October 13, 2011 at 10:29. Reason: added some files

 October 13, 2011, 10:16 #26 New Member   Werner Join Date: Dec 2009 Location: Austria Posts: 13 Rep Power: 8 HI Tom, no i dont got my continuity equation working correctly. Send me your solver, maybe i find your problem. Cheers Werner

 October 13, 2011, 10:40 #27 New Member   Tom Join Date: Sep 2011 Posts: 11 Rep Power: 7 HI Werner my solver is in the post above. I added another curly bracket and it works, but it doesnt make sense. i use bracket matching and indenting so i should be able to see where its missin.. I think my set up needs a setFields, so that the initial pressure is set before it starts to solve the fvm::laplacian(p)

 October 13, 2011, 10:43 #28 New Member   Werner Join Date: Dec 2009 Location: Austria Posts: 13 Rep Power: 8 Hi Tom, which vers. of OF you use?

 October 13, 2011, 11:19 #29 New Member   Tom Join Date: Sep 2011 Posts: 11 Rep Power: 7 Hi Nep Im using OpenFoam 2.0.1 Im having an issue with the boundary. I get the error message, gradientInternalCoeffs cannot be called for a calculatedFvPatchField. it suggests I migh be using a default boundary condition. I copied the boundary conditions from buoyantBoussinesqSimpleFoam I'll work on this some more tmw ( about 8 hours from now zzzzzzzzzzzzzzzz)

 February 21, 2014, 13:11 #30 Member   Marcus Letzel Join Date: Sep 2012 Location: Aurich Posts: 35 Rep Power: 6 I am just wondering whether this old thread has ever been solved. I think my thread may need a similar solution. Cheers, Marcus

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