# VOF Coefficient in freesurface cells

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 August 12, 2011, 02:12 VOF Coefficient in freesurface cells #1 New Member   mj Join Date: Apr 2011 Posts: 24 Rep Power: 8 Dear Friends I am simulating 2 phases (liquid-gas), 3D flow around ship and I want to capture wave height in far way. If I choose 0.1 as VOF for interface cells, my results would be match with experimental, while if I use cells with VOF=0.5 for freesurface, results are not accurate. I would appreciate if anyone send or introduce a reference which show I can use 0.1 for freesurface or not.

August 12, 2011, 13:13
#2
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Vieri Abolaffio
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Quote:
 Originally Posted by mrji8011 Dear Friends I am simulating 2 phases (liquid-gas), 3D flow around ship and I want to capture wave height in far way. If I choose 0.1 as VOF for interface cells, my results would be match with experimental, while if I use cells with VOF=0.5 for freesurface, results are not accurate. I would appreciate if anyone send or introduce a reference which show I can use 0.1 for freesurface or not.
definitly not,

to me it seems like a numerical diffusion problem. can you say in how many cells do you have the transition from vof 0 to 1? can you specify the model that you are using (implicit/explicit, transient or steady steate, wich solver, discretization order, wich vof reconstruction method, etc...)

August 13, 2011, 20:50
#3
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mj
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Quote:
 Originally Posted by sail definitly not, to me it seems like a numerical diffusion problem. can you say in how many cells do you have the transition from vof 0 to 1? can you specify the model that you are using (implicit/explicit, transient or steady steate, wich solver, discretization order, wich vof reconstruction method, etc...)
Thak you so much. the number of cells depend on vessel speed. roughly it is 3 cells. I am using implicit, transient,Gradient=Least Squares Based, Presuure= Presto, Momentun=Second order upwind, volume fration=Quick and second order implicit for transient formulation

August 18, 2011, 00:59
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mj
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Quote:
 Originally Posted by mrji8011 Thak you so much. the number of cells depend on vessel speed. roughly it is 3 cells. I am using implicit, transient,Gradient=Least Squares Based, Presuure= Presto, Momentun=Second order upwind, volume fration=Quick and second order implicit for transient formulation
do you think it is correct or not?

 August 18, 2011, 03:50 #5 Senior Member     Vieri Abolaffio Join Date: Jul 2010 Location: Always on the move. Posts: 308 Rep Power: 10 looks right. do you have experiemental data for the whole wake field or just where it touches the hull? if the latter is your case, could you please post a plot of the vof close to the hull, showing the mesh as well? i would like to check if the problem is just a sort of "numerical surfacial tension" ie high aspect ratio cell causes the flow to rise more that it is expected in the fist cell near the hull.

August 18, 2011, 22:08
#6
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mj
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Quote:
 Originally Posted by sail looks right. do you have experiemental data for the whole wake field or just where it touches the hull? if the latter is your case, could you please post a plot of the vof close to the hull, showing the mesh as well? i would like to check if the problem is just a sort of "numerical surfacial tension" ie high aspect ratio cell causes the flow to rise more that it is expected in the fist cell near the hull.
Please find the attacheds. I should capture waves in all domain.
Attached Images
 6.jpg (53.6 KB, 12 views) 61.jpg (21.5 KB, 9 views)

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