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-   -   Hentalpy equation openfoam - miss a term (http://www.cfd-online.com/Forums/openfoam/73321-hentalpy-equation-openfoam-miss-term.html)

lions85 March 4, 2010 11:15

Hentalpy equation openfoam - miss a term
 
Hi,
i'm working on my master thesis in wich i'm trying, starting from a SimpleFoam solver (steady, not transient), to programming in openfoam the ED, EDC and flamelets models in the way to compare the results with fluent and maybe in the future be able to use OF instead of fluent.

I made the EDmodel and tested it on the sandia simple flames: the results are quite good, but not excellent: the fluent flame has a higher peak and is more dissipative, and the difference seems to increase when the fuel inlet velocity decrease. In my opinion there is something wrong in the enthalpy equation.

Looking in the fluent user guide (http://my.fit.edu/itresources/manual...e568.htm#86361) we can see a term in the equation, named sensible enthalpy, that is the dissipation term due to the enthalpy of the single species.
This term is not in the hEqn file of Openfoam:
Code:

fvScalarMatrix hEqn
    (
        fvm::div(phi, h)
      - fvm::Sp(fvc::div(phi), h)
      - fvm::laplacian(turbulence->alphaEff(), h)
    -fvc::div(lambda*fvc::grad(TT))   

    ==
        fvc::div(phi/fvc::interpolate(rho)*fvc::interpolate(p))
      - p*fvc::div(phi/fvc::interpolate(rho))

The point is that i'm not able to add this term, because i really don't know how to access to the single elements enthalpy.
Probably my flame will not change with this therm and the differences will be the same but i want to try also in this way....

Thank you
Emanuele Leoni

SilPaut August 17, 2010 14:32

Quote:

Originally Posted by lions85 (Post 248573)
Hi,
i'm working on my master thesis in wich i'm trying, starting from a SimpleFoam solver (steady, not transient), to programming in openfoam the ED, EDC and flamelets models in the way to compare the results with fluent and maybe in the future be able to use OF instead of fluent.

I made the EDmodel and tested it on the sandia simple flames: the results are quite good, but not excellent: the fluent flame has a higher peak and is more dissipative, and the difference seems to increase when the fuel inlet velocity decrease. In my opinion there is something wrong in the enthalpy equation.

Looking in the fluent user guide (http://my.fit.edu/itresources/manual...e568.htm#86361) we can see a term in the equation, named sensible enthalpy, that is the dissipation term due to the enthalpy of the single species.
This term is not in the hEqn file of Openfoam:
Code:

fvScalarMatrix hEqn
    (
        fvm::div(phi, h)
      - fvm::Sp(fvc::div(phi), h)
      - fvm::laplacian(turbulence->alphaEff(), h)
    -fvc::div(lambda*fvc::grad(TT))   

    ==
        fvc::div(phi/fvc::interpolate(rho)*fvc::interpolate(p))
      - p*fvc::div(phi/fvc::interpolate(rho))

The point is that i'm not able to add this term, because i really don't know how to access to the single elements enthalpy.
Probably my flame will not change with this therm and the differences will be the same but i want to try also in this way....

Thank you
Emanuele Leoni


Hi Emanuele,
I have your same problem, have you understood what is happening there? do you find some solution? It would really help me :-)

Thank you
Silvano Pautasso

chandramurthy August 18, 2010 12:12

Exactly i had the same problem, when i tried the reactingfoam. Apparently i tried a reacting mixing layer problem [barrows&Kurkov]. the thermal diffusion is less in foam, giving a thin flame. I guessed something may be wrong with enthalpy equation., i could not go further deep into the code.

[QUOTE=lions85;248573]Hi,
the fluent flame has a higher peak and is more dissipative, and the difference seems to increase when the fuel inlet velocity decrease. In my opinion there is something wrong in the enthalpy equation.


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