Compression flux while solving alpha equation

kuria · May 20, 2019, 06:05

Hey Foamers

I had a question on how the compression flux is modeled in VOF model
In literature it is expressed as

Ur = min (C_alpha phi/Sf, max(phi/Sf) )nf (Eqn1)

where C_alpha, phi, Sf and nf are compression factor, velocity flux, magnitude of cell surface area, unit normal vector.

However in OpenFoam 6 it is written as
surfaceScalarField phic(mixture.cAlpha()*mag(phi/mesh.magSf()));

which would be Ur = C_alpha phi nf/Sf (Eqn2).

As I understand it, when C_alpha=1, both Eqn 1 and Eqn 2 are equivalent.

What do you all reckon did I misunderstand it ?

-Kurian

fedez91 · December 4, 2020, 14:42

You have probably figured this out already, but the literature shows how interFoam calculated the compression term in the version 2.x and older. That has been changed and now it is calculated the way you express it in your comment.

May 20, 2019, 06:05	Compression flux while solving alpha equation	#1
kuria Member K Join Date: Mar 2018 Posts: 34 Rep Power: 8	Hey Foamers I had a question on how the compression flux is modeled in VOF model In literature it is expressed as Ur = min (C_alpha phi/Sf, max(phi/Sf) )nf (Eqn1) where C_alpha, phi, Sf and nf are compression factor, velocity flux, magnitude of cell surface area, unit normal vector. However in OpenFoam 6 it is written as surfaceScalarField phic(mixture.cAlpha()*mag(phi/mesh.magSf())); which would be Ur = C_alpha phi nf/Sf (Eqn2). As I understand it, when C_alpha=1, both Eqn 1 and Eqn 2 are equivalent. What do you all reckon did I misunderstand it ? -Kurian

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December 4, 2020, 14:42		#2
fedez91 Member Federico Zabaleta Join Date: May 2016 Posts: 47 Rep Power: 9	You have probably figured this out already, but the literature shows how interFoam calculated the compression term in the version 2.x and older. That has been changed and now it is calculated the way you express it in your comment.