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Adding diffusion term to interFoam transport equation 

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August 30, 2017, 05:01 
Adding diffusion term to interFoam transport equation

#1 
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Join Date: Nov 2009
Posts: 111
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Dear Foamers,
I would like to add a diffusion term to the interFoam transport equation. Indeed, I want to simulate an airhydrogen mixture and diffusion due to concentration gradient is normally significant for such mixture. So, here is my thought process of what to do. Since I have never modified an OpenFoam solver before, I want to be sure that thatI am understanding each step and that I am doing things correctly. So the current transport equation for (one of the two phases/components) equation in interFoam is found in alphaEqn.H and equals to : and I understand that in this equation has been simplified because it is a solver for incompressible fluids. I would like to add the diffusion due to concentration. Based on the generic transport equation : So I understand that for interFoam solver, I must somehow include the following term, assuming diffusion term is constant and remembering to divide by due to its simplification in interFoam equation sinceit is for incompressible fluids I copy/pasted the interFoam solver directory to a personal directory and I understand that the code for [/math] \alpha_1 [math] transport equation is found in alphaEqn.H and I assume I should do the following modification : Code:
if (MULESCorr) { fvScalarMatrix alpha1Eqn ( ( LTS ? fv::localEulerDdtScheme<scalar>(mesh).fvmDdt(alpha1) : fv::EulerDdtScheme<scalar>(mesh).fvmDdt(alpha1) ) + fv::gaussConvectionScheme<scalar> ( mesh, phiCN, upwind<scalar>(mesh, phiCN) ).fvmDiv(phiCN, alpha1)  fvm:: laplacian(Gamma1/rho1, alpha1) ); Now in scalarTransportFoam.C:
Unfortunately, I do not master C language sufficiently nor OpenFoam structure/classes/functions to understand such subtleties and I would like to be sure I do the right thing and that I understand what I am doing. Also I see that for example, the function gaussConvectionScheme<scalar> requires additional parameters to work Code:
fv::gaussConvectionScheme<scalar> ( mesh, phiCN, upwind<scalar>(mesh, phiCN) ).fvmDiv(phiCN, alpha1) Eventually I see that Code:
LTS ? fv::localEulerDdtScheme<scalar>(mesh).fvmDdt(alpha1) : fv::EulerDdtScheme<scalar>(mesh).fvmDdt(alpha1) Once alphaEqn.H is fine, I have to add the new constant to CreateFileds.H Code:
Info<< "Reading transportProperties\n" << endl; immiscibleIncompressibleTwoPhaseMixture mixture(U, phi); volScalarField& alpha1(mixture.alpha1()); volScalarField& alpha2(mixture.alpha2()); const dimensionedScalar& rho1 = mixture.rho1(); const dimensionedScalar& rho2 = mixture.rho2(); const dimensionedScalar& Gamma1= mixture.Gamma1(); Once those changes have been confirmed to be fine, I will pursue with the modifications of the OpenFoam dictionnaries as instructed in this tutorial Last edited by Gearb0x; August 30, 2017 at 07:52. 

August 30, 2017, 05:37 

#2 
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Brian Willis
Join Date: Mar 2011
Location: Cape Town, South Africa
Posts: 58
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Dear GearB0x
This seems like a case where interFoam, which uses interface compression and the MULES algorithm to decrease the effects of numerical diffusion at the interface between two immiscible phases, and probably will not be the ideal solver for the mixing of your two gases. Have you considered looking at a two phase EulerEuler solver like twoPhaseEulerFoam or reactingTwoPhaseEulerFoam? Regards, Brian 

August 30, 2017, 07:51 

#3 
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Join Date: Nov 2009
Posts: 111
Rep Power: 16 
I want to use interFoam as a first step because it is a simpler solver i.e. incompressible, no heat transfer.


February 14, 2023, 04:16 

#4 
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Join Date: Oct 2022
Posts: 24
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Did you manage to add the diffusion term?


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