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Signs used in advecting volume fractions in interfoam

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Old   June 29, 2017, 16:42
Default Signs used in advecting volume fractions in interfoam
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Katt
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Hi,

I am aware of the standard equation used to advect volume fractions and about the derivation regarding "interface compression" that interfoam solver uses.

Coming to the code in "alphaEqn.H", I have the following two questions:
Code:
surfaceScalarField phic = mag(phi/mesh.magSf());                      
phic = min(interface.cAlpha()*phic, max(phic));                      
 surfaceScalarField phir = phic*interface.nHatf();                        
   for (int aCorr=0; aCorr<nAlphaCorr; aCorr++)                      
     {                       
      surfaceScalarField phiAlpha =   
                                  fvc::flux ( phi,  
                                  alpha1,                       
                                  alphaScheme  )
                               + fvc::flux ( -fvc::flux(-phir, scalar(1) - alpha1, alpharScheme),
                                               alpha1,
                                              alpharScheme );
Q1) I don't really understand the sign convention used for the compression term.
In the relative flux term: -fvc::flux(-phir, ---). So, arent you finally adding an additional convective term to the first term of "phi*alpha1"?

Q2) If C-alpha =1 and considering the relative velocity acts as a shock front against the original convective term, wouldnt both the flux term and the relative flux term balance each other and cancel out leading to no advection?

I do realise my imagination is wrong as I do see correct flow behaviour. Can anyone enlighten me.

Thanks;
Katt
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