CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Software User Forums > OpenFOAM > OpenFOAM Running, Solving & CFD

Problem with Diffusion Equation Implementation

Register Blogs Members List Search Today's Posts Mark Forums Read

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   February 22, 2019, 12:45
Default Problem with Diffusion Equation Implementation
  #1
Member
 
Raunak Bardia
Join Date: Jan 2015
Posts: 32
Rep Power: 9
raunakbardia is on a distinguished road
Hi all,

I am using OpenFOAM v1706 and trying to make some additions to the interFlow solver.

I have initialized a field that is concentrated at the interfacial cells of my two-phase system. It is shown by the attached image (InitialCondition.jpg). I use a simple diffusion equation to diffuse this field on the rest of the grid. The result is shown in the second image (Diffused.jpg). Clearly, the circular symmetry is lost and it has to be due to some error in my implementation of the diffusion equation. But the volume integration of the initial source is conserved to the tolerance level that was specified.

Here is my source code used for the diffusion equation

spreadSource.H
Code:
const dimensionedScalar mdotDiffusionConstant("diff",dimArea,dict_.lookupOrDefault<scalar>("mdotDiffusionConstant",1000));

mdot1 = mdot0; // mdot0 stores the initial condition
fvScalarMatrix mdotSpreadEqn
(
    fvm::laplacian(mdotDiffusionConstant, mdot1)
);
mdotSpreadEqn.solve();
The mdot fields were created as follows.

createFields.H
Code:
// Calculating Source Term at Interfacial Cells
volScalarField mdot0
(
    IOobject
    (   
        "mdot0",
        runTime.timeName(),
        mesh,
        IOobject::NO_READ,
        IOobject::AUTO_WRITE
    ),  
    mesh,
    dimensionedScalar("zero",dimensionSet(1,-3,-1,0,0,0,0),0.0)
);

// Distributing Source Term in the domain
volScalarField mdot1
(
    IOobject
    (   
        "mdot1",
        runTime.timeName(),
        mesh,
        IOobject::NO_READ,
        IOobject::AUTO_WRITE
    ),  
    mesh,
    dimensionedScalar("zero",dimensionSet(1,-3,-1,0,0,0,0),0.0),
    mdotBoundaries
);
Here is the fvSolution file I am using:

fvSolution
Code:
solvers
{
    "alpha.water.*"
    {
        interfaceMethod "isoAdvector";
        isoFaceTol      1e-8;
        surfCellTol     1e-8;
        snapAlphaTol    1e-8;
        nAlphaBounds    3;
        clip            true;
        writeIsoFaces   false;
        writeInterfaceDetails   true;
        phaseChange true;
        prescribedmdot  true;
        massfluxvalue   -100.0;

        nAlphaCorr      2;
        nAlphaSubCycles 1;
        cAlpha          1;  

        MULESCorr       yes;
        nLimiterIter    3;  

        solver          smoothSolver;
        smoother        symGaussSeidel;
        tolerance       1e-8;
        relTol          0;  
        mdotDiffusionConstant   6.25e-08;
    }   

    pcorr
    {   
        solver          PCG;
        preconditioner  DIC;
        tolerance       1e-10;
        relTol          0;  
    }   

    p_rgh
    {   
        solver          PCG;
        preconditioner  DIC;
        tolerance       1e-07;
        relTol          0.05;
    }   

    p_rghFinal
    {   
        $p_rgh;
        tolerance       1e-07;
        relTol          0;  
    }   
    mdot1
    {   
        solver          PCG;
        preconditioner  DIC;
        tolerance       1e-8;
        relTol          0.1;
    }
    mdot1Final
    {
        $mdot1;
    }
    U
    {
        solver          PBiCG;
        preconditioner  DILU;
        tolerance       1e-06;
        relTol          0;
    }
}

PIMPLE
{
    momentumPredictor no;
    nCorrectors     -1;
    nNonOrthogonalCorrectors -1;
    nAlphaCorr      1;
    nAlphaSubCycles 1;
    cAlpha          1;
    pRefCell        0;
    pRefValue       0;
}

SIMPLE
{
    nNonOrthogonalCorrectors 0;
}
I believe that implementation of a Diffusion equation should be straightforward in OpenFOAM. Any help will be much appreciated.

Thanks.
Attached Images
File Type: jpg InitialCondition.jpg (25.9 KB, 13 views)
File Type: jpg Diffused.jpg (32.4 KB, 12 views)
raunakbardia is offline   Reply With Quote

Old   February 25, 2019, 04:04
Default
  #2
Senior Member
 
Robert
Join Date: May 2015
Location: Bremen, GER
Posts: 292
Rep Power: 10
RobertHB is on a distinguished road
Did you allready take a look at the scalarTransportFoam solver? It solves an advection-diffusion equation. Maybe you can take parts of that eqn. and implement it into your solver.
__________________
If you liked my answer to your question, please consider leaving a "Like" in return
RobertHB is offline   Reply With Quote

Reply

Tags
diffusion equation, interface advection, openfoam 1706, solver

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Setting the height of the stream in the free channel kevinmccartin CFX 12 October 13, 2022 22:43
turbulent diffusion term in transport equation for additional variables Raijin Thunderkeg CFX 2 May 17, 2014 23:53
Problem in discretising the governing equation. sahilkala50 Main CFD Forum 2 September 4, 2013 06:45
problem on energy and flow equation solving separately preetam69 FLUENT 2 July 30, 2013 22:08
Radial diffusion in scalarTransport problem jr33 OpenFOAM 0 April 16, 2013 19:22


All times are GMT -4. The time now is 22:22.