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-   -   interFoam and alphaEqn.H (http://www.cfd-online.com/Forums/openfoam-programming-development/100397-interfoam-alphaeqn-h.html)

pablodecastillo April 25, 2012 04:50

interFoam and alphaEqn.H
 
Hello,

Why in alphaEqn.H is it not added alpha1 = max(min(alpha1, scalar(1)), scalar(0)); i mean this artificial bounded?

Thanks

Phicau April 25, 2012 05:55

Hi

MULES solver ensures boundedness, that is why the last 2 inputs are 0 and 1, the bounds of alpha1. This is achieved by the use of limiters.

The final result may show values greater than 1 or lower than 0, but with differences of the order of 10^-5, which is negligible.

Regards

santiagomarquezd May 1, 2012 08:52

Using an artificial bounding of this kinds leads to a non-phase-preserving algorithm due it 'cuts' with having in account the conservative properties of the alpha equation. In other words you will lose or gain mass.

Regards.

pablodecastillo May 7, 2012 13:57

But looking for steady state loss or gain mass is not going to be relevant or yes?

Thanks

santiagomarquezd May 8, 2012 12:59

Hhmm, I don't know, but since the solver is unsteady probably it will blow up before reach the steady state due mass preservation problems.

Regards.

Saideep March 28, 2016 10:47

Hi guys,

I guess this is the most relevant thread I found to post the following question and hope anyone of you could help me out.
The alphaEqn.H file has evolved from 2.2 version to 2.3 version. I can understand the 2.2 version of the code but I cant follow most part of the 2.3 version of alphaEqn. Can you help me out?

What does the following code indicate?
fvScalarMatrix alpha1Eqn
(
fv::EulerDdtScheme<scalar>(mesh).fvmDdt(alpha1)
+ fv::gaussConvectionScheme<scalar>
(
mesh,
phi,
upwind<scalar>(mesh, phi)
).fvmDiv(phi, alpha1)
);

The later part is from the older version for advection of alpha with velocity and relative velocity terms.

I tried to use the older version into this but alpha is no more bounded between 0 and 1.

Thanks;
Saideep

santiagomarquezd April 16, 2016 21:00

Hi Saideep, the new version of alphaEqn is based on operator splitting techniques to obtain a semi-implicit solver. The code you posted corresponds to the first-order bounded predictor of alpha which is lately corrected by a high-order corrector:

http://www.openfoam.org/version2.3.0/multiphase.php

Regards.


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