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alpha or alpha1 in interFoam & interDyMFoam

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Old   September 8, 2009, 06:45
Default alpha or alpha1 in interFoam & interDyMFoam
  #1
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T Somerville
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From the damBreak tutorial of version 1.5, fvSchemes looks like:

gradSchemes
{
default Gauss linear;
grad(U) Gauss linear;
grad(gamma) Gauss linear;
}

divSchemes
{
div(rho*phi,U) Gauss limitedLinearV 1;
div(phi,gamma) Gauss vanLeer;
div(phirb,gamma) Gauss interfaceCompression;
}

Now, I was under the impresssion that gamma was replaced by alpha1 in version 1.6. Yet, here is the same excerpt from v1.6 damBreak tutorial, which contains alpha and alpha1:

gradSchemes
{
default Gauss linear;
grad(U) Gauss linear;
grad(alpha1) Gauss linear;
}

divSchemes
{
div(rho*phi,U) Gauss limitedLinearV 1;
div(phi,alpha) Gauss vanLeer;
div(phirb,alpha) Gauss interfaceCompression;
}

and it isn't even consistent - take a look at the same excerpt from interDyMFoam v1.6

gradSchemes
{
default Gauss linear;
grad(U) Gauss linear;
grad(alpha) Gauss linear;
}

divSchemes
{
div(rho*phi,U) Gauss upwind;
div(phi,alpha) Gauss vanLeer;
div(phirb,alpha) Gauss interfaceCompression;
}

So what is the difference between alpha and alpha1. Am I misunderstanding something, or is this a bug?

Cheers,
Tracy.
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Old   September 9, 2009, 02:54
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alpha1 is the phase fraction of phase 1 in a multi-phase system, alpha in the control dictionaries refers to any phase. The reason for the "inconsistency" is to ensure that the discretisation schemes are the same for all phases.

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Old   September 9, 2009, 21:23
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Thank you.

But the "inconsistency" refers to the line
grad(alpha1) Gauss linear;
in the controlDict of the interFoam tutorial,

compared to the line
grad(alpha) Gauss linear;
in the controlDict of the interDyMFoam tutorial.

I'm assuming from your reply that they should both be grad(alpha)?
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Old   September 10, 2009, 02:51
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Ahh OK, I missed that, it should be grad(alpha1) in both cases but as the scheme is set the same as the default it won't make any difference. I will correct this in 1.6.x.

Thanks

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