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October 19, 2005, 16:19 
Does nayone knows if OpenFoam

#1 
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Muzio Grilli
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Does nayone knows if OpenFoam is able to simulate a porous material.
Please answer 

October 19, 2005, 23:29 
I think it depends on what do

#2 
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Billy
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I think it depends on what do you want to simulate.
OpenFOAM is flexible and can simulate many things. If there is no application that suits your needs, you can always build your own. 

October 20, 2005, 05:27 
You simply have to add the Dar

#3 
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Bernhard Gschaider
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You simply have to add the Darcyterm to the velocityequations (in other words: write a solver for this)
But there is no outofthebox solver for this (and there is always the problem how you define which parts of the geometry are porous and which are not)
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October 20, 2005, 12:09 
so substantially you are telli

#4 
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Muzio Grilli
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so substantially you are telling me that i have to connect two different solvers, one when i'm out of the box and another one when i'm in the box, have you ever done something like this?


October 20, 2005, 12:22 
Sorry. With "outofthebox" I

#5 
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Bernhard Gschaider
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Sorry. With "outofthebox" I meant "a solver available in the OFdistribution". You'll have to write a solver yourself.
One approach would be to simply extend an existing solver by adding Darcy as a sourceterm. In the Darcyterm there is a permeability/resistivity (whatever formulation you prefer). By using a field for that and specifying appropriate values for certain regions you can define porous/nonporouszones. That approach has some problems at the porous/nonporousinterfaces.
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October 20, 2005, 12:40 
You're telling me to treat it

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Muzio Grilli
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You're telling me to treat it as a boundary condition?
I have to make the flux pass through a zone which i define as a porous zone and i have to evaluate the consequent pressure loss Sorry if i'm a little bit boring but i have to do this as a thesis job, so what kind of approach do you think would be best? 

October 24, 2005, 07:14 
@boundary condition: No. You j

#7 
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@boundary condition: No. You just implement an additional sourceterm. I just wanted to warn you, that there might be problems at the porous/nonporousinterface
Is your whole simulation domain a porous body with a homogenous permeability or is your setup of the type: inlet/NaviesStokesFlow/porous body (Darcy)/NSFlow/outlet? My above comments were always meant for the second case.
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October 24, 2005, 15:22 
I'm in the second condition,wi

#8 
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Muzio Grilli
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I'm in the second condition,with inlet, NS flow, porous body, NS flow, and outlet.
Do you know a different approach to avoid the problems at the porous non porous inteface? 

October 24, 2005, 18:31 
No. Sorry. But I'll tell you w

#9 
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Bernhard Gschaider
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No. Sorry. But I'll tell you when I find out.
Anyway: these effects are only significant for low permeabilities.
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October 25, 2005, 06:48 
I found the NavierStokesBrin

#10 
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Muzio Grilli
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I found the NavierStokesBrinkman equation
which is U*grad(U)nu*laplacian(U)nu*U/K=(1/rho)*grad(p) where nu is the kinematic viscosity and K represents the permeability tensor. So I should simply add the term nu*U/K I looked at simpleFoam solver and i found this tmp<fvvectormatrix> UEqn ( fvm::div(phi, U) + turbulence>divR(U) ); UEqn().relax(); solve(UEqn() == fvc::grad(p)); I have some questions 1)Where is the division by rho regarding grad(p), because i foundend in the programmer guide that R represents nu(eff)*gradU and nu is the kinematic visvosity. 2)If the equation is right i should simply define the K tensor in the porous media domain the change the equation to this form tmp<fvvectormatrix> UEqn ( fvm::div(phi, U) + turbulence>divR(U)+(nu/K)*U ); UEqn().relax(); solve(UEqn() == fvc::grad(p)); Please tell me if i've made some syntax error 

October 25, 2005, 07:12 
This looks good. I would sugge

#11 
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Bernhard Gschaider
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This looks good. I would suggest using fvm::Sp or fvm::SuSp for an implicit treatment of the source term.
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October 25, 2005, 07:21 
You mean like this
tmp

#12 
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Muzio Grilli
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You mean like this
tmp<fvvectormatrix> UEqn ( fvm::div(phi, U) + turbulence>divR(U)+nu*fvm::SuSp(U,G) ); UEqn().relax(); solve(UEqn() == fvc::grad(p)); P.S. ; I'dont have to worry about the lack of density? 

October 25, 2005, 07:23 
Sorry G is the inverse of K te

#13 
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Muzio Grilli
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Sorry G is the inverse of K tensor


October 25, 2005, 07:28 
If you switch positions of U a

#14 
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Bernhard Gschaider
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If you switch positions of U and G: Yes.
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October 25, 2005, 11:57 
Sorry Bernhard but from my que

#15 
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Muzio Grilli
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Sorry Bernhard but from my questions i think you understood i'm very new in using OpenFoam, so i need some more hints, i know i'm boring, i'm trying to define the field of the permeability tensor and i really don't know how to begin.
I thaught to convert setGammaDambreak utility to my case but it only defines the initial field and it works on an already existing field it doesn't define a new one. In createFields.H i also observed that it creates the fields reading from existing files. Futhermore i think I should define the field as a volTensorField so that it refers to cell centers or i have to define it as a pointfield Please answer 

October 25, 2005, 13:31 
Density: the incompressible co

#16 
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Mattijs Janssens
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Density: the incompressible codes tend to solve for U/rho, p/rho etc. (see the dimensions in the fields) with density set to 1.


October 28, 2005, 06:59 
Hi Muzio!
When developing a

#17 
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Bernhard Gschaider
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Hi Muzio!
When developing a new solver you should be prepared to edit the files for the initial conditions. Copy an existing fieldfile (p for example) and edit it: 1. set the correct dimensions 2. set correct boundary conditions (zeroGradient should be alright for the permeability). The you can use damBreakderived utility on that (or you might have a look at the setFieldsutility which is new in 1.2 and might just do what you're looking for). @tensorField: do you have directed permeabilities? if not a scalar would be sufficient.
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November 7, 2005, 08:31 
Hi Bernhard I wrote the solver

#18 
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Muzio Grilli
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Hi Bernhard I wrote the solver and i used it but i had very bad results (negative pressure for example).
I found that when i write nu*fvm::SuSp(U,G) this only discretizes G in a implicit or explicit way depending on the sign of U, and that is not correct, so i discretized it as an explicit term This is the .C file I used #include "fvCFD.H" #include "incompressible/singlePhaseTransportModel/singlePhaseTransportModel.H" #include "incompressible/turbulenceModel/turbulenceModel.H" // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * // int main(int argc, char *argv[]) { # include "setRootCase.H" # include "createTime.H" # include "createMesh.H" # include "createFields.H" # include "created.H" # include "createG.H" # include "createNu.H" # include "initContinuityErrs.H" //mesh.clearPrimitives(); // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * // Info<< "\nStarting time loop\n" << endl; for (runTime++; !runTime.end(); runTime++) { Info<< "Time = " << runTime.timeName() << nl << endl; # include "readSIMPLEControls.H" p.storePrevIter(); // Pressurevelocity SIMPLE corrector { // Momentum predictor tmp<fvvectormatrix> UEqn ( fvm::div(phi, U) + (1.0+2.5*(1.0d))*turbulence>divR(U)+nu*G*U ); UEqn().relax(); solve(UEqn() == fvc::grad(p)); p.boundaryField().updateCoeffs(); volScalarField AU = UEqn().A(); U = UEqn().H()/AU; UEqn.clear(); phi = fvc::interpolate(U) & mesh.Sf(); adjustPhi(phi, U, p); // Nonorthogonal pressure corrector loop for (int nonOrth=0; nonOrth<=nNonOrthCorr; nonOrth++) { fvScalarMatrix pEqn ( fvm::laplacian(1.0/AU, p) == fvc::div(phi) ); fvScalarMatrix::reference pRef = pEqn.setReference(pRefCell, pRefValue); pEqn.solve(); pEqn.unsetReference(pRef); if (nonOrth == nNonOrthCorr) { phi = pEqn.flux(); } } # include "continuityErrs.H" // Explicitly relax pressure for momentum corrector p.relax(); // Momentum corrector U = fvc::grad(p)/AU; U.correctBoundaryConditions(); } turbulence>correct(); runTime.write(); Info<< "ExecutionTime = " << runTime.elapsedCpuTime() << " s\n\n" << endl; } Info<< "End\n" << endl; return(0); } // ********** PLEASE HELP ME find out where is my error 

November 7, 2005, 11:41 
what error?
first though, n

#19 
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Niklas Nordin
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what error?
first though, nu*fvm::SuSp(U,G) is not the same as fvm::SuSp(nu*G, U) which is what you should use, second: why cant the pressure be negative? 

November 7, 2005, 12:20 
I'm analysing the flow of an i

#20 
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Muzio Grilli
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I'm analysing the flow of an incompressible fluid through a porous media inside and outside it, the therm which i have to introduce is ((nu)/K)*U
writing fvm::SuSp(nu*G,U)where G=(K)^1 i discretize only U and not the product ((nu)*G)*U 

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