- **OpenFOAM Bugs**
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- - **alpha or alpha1 in interFoam & interDyMFoam**
(*https://www.cfd-online.com/Forums/openfoam-bugs/68140-alpha-alpha1-interfoam-interdymfoam.html*)

alpha or alpha1 in interFoam & interDyMFoamFrom 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. |

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.
H |

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)? |

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 H |

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