# AlphaCourantNo code

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 June 18, 2013, 05:18 AlphaCourantNo code #1 Member   Join Date: Mar 2013 Posts: 94 Rep Power: 5 Hi to all I want to know how is calculated AlphaCourantNo so I look for the code and I find this lines. if (mesh.nInternalFaces()) { scalarField sumPhi ( pos(alpha1 - 0.01)*pos(0.99 - alpha1) *fvc::surfaceSum(mag(phi))().internalField() ); alphaCoNum = 0.5*gMax(sumPhi/mesh.V().field())*runTime.deltaTValue(); } My understanding of this piece of code is that for each cell it sums the face flux magnitudes, divides it by the cell volume and multiplies it with deltaT/2. The maximum over all cells is then the Courant number. But I don't understand the meaning of this term: pos(alpha1 - 0.01)*pos(0.99 - alpha1) Anyone kwon the meaning of it? Thank to all

May 25, 2014, 09:07
#2
New Member

enzhen zhang
Join Date: Dec 2013
Location: Shanghai,China
Posts: 11
Rep Power: 4
Quote:
 Originally Posted by giack Hi to all I want to know how is calculated AlphaCourantNo so I look for the code and I find this lines. if (mesh.nInternalFaces()) { scalarField sumPhi ( pos(alpha1 - 0.01)*pos(0.99 - alpha1) *fvc::surfaceSum(mag(phi))().internalField() ); alphaCoNum = 0.5*gMax(sumPhi/mesh.V().field())*runTime.deltaTValue(); } My understanding of this piece of code is that for each cell it sums the face flux magnitudes, divides it by the cell volume and multiplies it with deltaT/2. The maximum over all cells is then the Courant number. But I don't understand the meaning of this term: pos(alpha1 - 0.01)*pos(0.99 - alpha1) Anyone kwon the meaning of it? Thank to all
I have the same question.Does anyone know the meaning?

 May 30, 2014, 08:47 #3 New Member   Daniel Deising Join Date: Feb 2013 Location: Darmstadt, Germany Posts: 1 Rep Power: 0 Hi enzhen, this line Code: `pos(alpha1 - 0.01)*pos(0.99 - alpha1)` gives you all cells where the volumetric phase fraction takes values between 0.01 and 0.99. And this piece of code Code: `0.5*gMax(sumPhi/mesh.V().field())*runTime.deltaTValue();` is the definition of the Courant number in multiple dimensions, assuming that the calculated velocity field is divergence free. So as a result, you obtain a Courant number in the interfacial area. Hope this helps, Best, Daniel babakflame likes this.

May 31, 2014, 12:58
#4
New Member

enzhen zhang
Join Date: Dec 2013
Location: Shanghai,China
Posts: 11
Rep Power: 4
Quote:
 Originally Posted by danieldeising Hi enzhen, this line Code: `pos(alpha1 - 0.01)*pos(0.99 - alpha1)` gives you all cells where the volumetric phase fraction takes values between 0.01 and 0.99. And this piece of code Code: `0.5*gMax(sumPhi/mesh.V().field())*runTime.deltaTValue();` is the definition of the Courant number in multiple dimensions, assuming that the calculated velocity field is divergence free. So as a result, you obtain a Courant number in the interfacial area. Hope this helps, Best, Daniel
thanks ~that does help

 Tags alpha1, courant number, interfoam

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