CFD Online Discussion Forums - combustion does not occur with reactingFoam

CFD Online Discussion Forums (https://www.cfd-online.com/Forums/)

- OpenFOAM Running, Solving & CFD (https://www.cfd-online.com/Forums/openfoam-solving/)

- - combustion does not occur with reactingFoam (https://www.cfd-online.com/Forums/openfoam-solving/253230-combustion-does-not-occur-reactingfoam.html)

combustion does not occur with reactingFoam

Hello,
I am trying to simulate a flammable gas flow in atmosphere with reactingFoam. You can find the whole case directory attached at the end.

If I do not ignite the gas (/constant/combustionProperties --> active off and /constant/chemistryProperties --> chemistry off) the gas leak is totally diffusive and results are good.
However, if I try to ignite the flammable gas (/constant/combustionProperties --> active on and /constant/chemistryProperties --> chemistry on) the reaction does not occur. Therefore the results are exactly the same as withouth ignition.

The reaction is a single-step reaction, implemented in /constant/reactionGRI.

reactionGRI

Code:

elements

(

)

;



species

4

(

H2

O2

H2O

N2

)

;





reactions

{

    un-named-reaction-2

    {

        type            irreversibleinfiniteReaction; 

        reaction        "2H2 + O2 + 3.79N2 = 2H2O + 3.79N2";

    }

}

chemistryProperties

Code:

/*--------------------------------*- C++ -*----------------------------------*\

| =========                 |                                                 |

| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |

|  \\    /   O peration     | Version:  v2012                                 |

|   \\  /    A nd           | Website:  www.openfoam.com                      |

|    \\/     M anipulation  |                                                 |

\*---------------------------------------------------------------------------*/

FoamFile

{

    version     2.0;

    format      ascii;

    class       dictionary;

    location    "constant";

    object      chemistryProperties;

}

// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //



chemistryType

{

    chemistrySolver   ode;

    chemistryThermo   psi;

    TDAC              off;

}



initialChemicalTimeStep 1e-07;



chemistry       on;



odeCoeffs

{

    solver          seulex;  // Rosenbrock34, seulex or rodas23

    absTol          1e-12;

    relTol           1e-7;

}



// ************************************************************************* //

combustionProperties

Code:

/*--------------------------------*- C++ -*----------------------------------*\

| =========                 |                                                 |

| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |

|  \\    /   O peration     | Version:  v2012                                 |

|   \\  /    A nd           | Website:  www.openfoam.com                      |

|    \\/     M anipulation  |                                                 |

\*---------------------------------------------------------------------------*/

FoamFile

{

    version     2.0;

    format      ascii;

    class       dictionary;

    location    "constant";

    object      combustionProperties;

}

// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //



combustionModel  EDC;



active  on;



EDCCoeffs

{

    version v2005;

}



// ************************************************************************* //

thermophysicalProperties

Code:

/*--------------------------------*- C++ -*----------------------------------*\

| =========                 |                                                 |

| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |

|  \\    /   O peration     | Version:  v2012                                 |

|   \\  /    A nd           | Website:  www.openfoam.com                      |

|    \\/     M anipulation  |                                                 |

\*---------------------------------------------------------------------------*/

FoamFile

{

    version     2.0;

    format      ascii;

    class       dictionary;

    location    "constant";

    object      thermophysicalProperties;

}

// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //



thermoType

{



    type            hePsiThermo;

    mixture        reactingMixture; //singleStepReactingMixture;

    transport       sutherland;

    thermo          janaf;

    energy          sensibleEnthalpy;

    equationOfState perfectGas;

    specie          specie;

}



inertSpecie N2;



chemistryReader foamChemistryReader;

foamChemistryFile "<constant>/reactionsGRI";

foamChemistryThermoFile "<constant>/thermo.compressibleGasGRI";



dpdt false;



 // ************************************************************************* //

I have the following question:

1) Why does the reaction not occur?

2) Is irreversibleinfiniteReaction in /constant/reactionGRI correct? Maybe is it not fast enough to show something in a short time?

3) In /constant/thermophysicalProperties should be selected mixture reactingMixture or singleStepReactingMixture?

4) Could be the problem the lack of ignition?

Really thank for your help.

Try to use another turbulence model. For example RNG instead of standard k-e-model.
Please see this post

https://www.cfd-online.com/Forums/op...ial-error.html.
May be it will help you.
Good luck!

Quote:

Originally Posted by kerim (Post 861049)

Try to use another turbulence model. For example RNG instead of standard k-e-model.
Please see this post

https://www.cfd-online.com/Forums/op...ial-error.html.
May be it will help you.
Good luck!

@kerim thank you for your answer. I followed your tips and switched standard k-eps model to RNG k-eps model in turbulenceProperties... but the results do not show any combustion, only diffusion.

Code:

/*--------------------------------*- C++ -*----------------------------------*\

| =========                 |                                                 |

| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |

|  \\    /   O peration     | Version:  v2012                                 |

|   \\  /    A nd           | Website:  www.openfoam.com                      |

|    \\/     M anipulation  |                                                 |

\*---------------------------------------------------------------------------*/

FoamFile

{

    version     2.0;

    format      ascii;

    class       dictionary;

    location    "constant";

    object      turbulenceProperties;

}

// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //



simulationType   RAS;



RAS

{

    RASModel        RNGkEpsilon;



    kEpsilonCoeffs

    {

        Prt 1;        

    }



    turbulence      on;

    printCoeffs     on;

}



// ************************************************************************* //

Edoardo1993,

Per your original post, I would suggest changing the reaction in reactionsGRI from irreversibleinfiniteReaction to irreversibleArrheniusReaction. You can then adjust the Arrhenius rate constants and activation temperature until you get a reaction. If ignition/combustion still does not occur, re-running with alternative RAS models per Kerim is also advised.

Notably, irreversibleArrheniusReaction is only used in conjunction with LES turbulence in the combustion tutorials.

Quote:

Originally Posted by tas38 (Post 861104)

Thank you tas38. I did not know about LES and irreversibleinfiniteReaction.

Now, my reaction file is:

Code:

reactions

{

    un-named-reaction-2

    {

        type         irreversibleArrheniusReaction;

        reaction        "2H2 + O2 + 3.79N2 = 2H2O + 3.79N2";

        A        5.2e16;

        beta     0;

        Ta       14906;

    }

}

Reaction does not occur yet, with both standard k-eps and RNG k-eps models. I think the problem is the lack of ignition, because there are not hot spots in the domain.

Edoardo1993,

Yes, you could try adding an ignition source (small box with high temperature) using setFieldsDict containing a boxToCell region as in DLR_A_LTS.

However, if I recall, the EDC model should not require a direct ignition source. Combustion is initiated simply due the presence of turbulence, i.e.

and $\epsilon$ .

I just noticed in your combustionProperties file you have active on;, however, I believe this should be active true;. Not sure if no vs. true makes a difference, but I would try this first.

Quote:

Originally Posted by tas38 (Post 861156)

Edoardo1993,
Yes, you could try adding an ignition source (small box with high temperature) using setFieldsDict containing a boxToCell region as in DLR_A_LTS.
However, if I recall, the EDC model should not require a direct ignition source. Combustion is initiated simply due the presence of turbulence, i.e.

and $\epsilon$ .
I just noticed in your combustionProperties file you have active on;, however, I believe this should be active true;. Not sure if no vs. true makes a difference, but I would try this first.

tas38, thank you for your kind help.
I knew that active true and on are the same keyword.
Regarding ignition with EDC model, I created another directory for test and the combustion starts only when the flammable flow touches an hot spot, in my case a wall with T=1000K (probably you can get similar result with setFieldDict). I don't see any reaction to occur when this wall is cold.

What do you mean with "Combustion is initiated simply due the presence of turbulence, i.e.

and $\epsilon$ "? The greater k and epsilon, the faster the reaction?

Hello. I hope someone can help me because I am still stucked with this issue.
I finally managed to ignite the gas with fvOptions setting some cells at 1200K. The problem is the simulation is running only when using CH4.
As soon as I switch the gas to H2 (changing the reaction with "H2 + 2O2 = 2H2O" and the thermo.compressibleGas ), the simulation starts but it stops because of several errors..

Code:

elements

(

O

C

H

N

);





species

(

    O2

    H2O

    CH4

    CO2

    N2

);



reactions

{

    methaneReaction

    {

        type     irreversibleArrheniusReaction;

        reaction "CH4 + 2O2 = CO2 + 2H2O";

        A        5.2e16;

        beta     0;

        Ta       14906;

    }

 }

Furthermore, I have another question. I attempted to integrate the GRI reactions, which I found in the SANDIAD_LTS tutorial, into the working model with CH4. Why does the reaction occur with the single-step reaction but not with the GRIMECH file?"

Hello. I want to simulate a combustion model through EDC model based on reactingFoam. Could you please show me a tutorial about EDC implementation? Thank you very much!