# Density averaging the surface tension term in interFoam

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March 30, 2022, 12:32
Density averaging the surface tension term in interFoam
#1
Member

Venkat Ganesh
Join Date: May 2020
Location: Cincinnati, Ohio
Posts: 49
Rep Power: 4
Hey multiphase researchers, I'm trying a standard modification to the surface tension term in interFoam which has been suggested in Brackbill's paper on CSF method, which is to include a density averaging term in the surface tension force term calculation. (I've shared an image of the equation)

In code within openfoam, the current surface tension force term without the density averaging is implemented as
Code:
`fvc::interpolate(sigmaK())*fvc::snGrad(alpha1)`
I obtained the code for density averaged surface tension term from the post (In attempt to decrease spurious currents in VOF) through Kevin's github adaption (https://github.com/floquation/OF-kva...faceProperties). It is written as
Code:
`fvc::interpolate(sigmaK()*rho)*fvc::snGrad(alpha1)*2/(rho1+rho2)`
He has shared a detailed explanation of how the equation is arrived and while it all made perfect sense, adopting the change to interFoam is giving me very poor results in terms of bubble shapes, bubble departure diameters and times. I'm finding that that adaption is causing a severely elongated bubble instead of the typical spherical shapes and that the departure diameters and times are overpredicted. I was wondering if someone else had any luck adopting the density averaging approach from Brackbill's paper and if there is an alternate way of expressing that in code?

I'm sharing an image of the bubble shape I obtained using the current code for reference. It would be great if someone could confirm if they've faced similar issues with adopting the change as well.

"Brackbill, J. U., Kothe, D. B., & Zemach, C. (1992). A continuum method for modeling surface tension. Journal of computational physics, 100(2), 335-354."
Attached Images
 Surface tension term.JPG (15.4 KB, 7 views) Bubble Shape.jpg (61.2 KB, 8 views)

 Tags csf model, interfoam, surface tension