Hentalpy equation openfoam - miss a term

lions85 · March 4, 2010, 10:15

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

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.

March 4, 2010, 10:15	Hentalpy equation openfoam - miss a term	#1
lions85 New Member Emanuele Leoni Join Date: Apr 2009 Posts: 13 Rep Power: 16	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(lambdafvc::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

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August 18, 2010, 12:12		#3
chandramurthy Member MSR CHANDRA MURTHY Join Date: Mar 2009 Posts: 33 Rep Power: 17	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.