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-   -   VOF Coefficient in freesurface cells (http://www.cfd-online.com/Forums/fluent/91479-vof-coefficient-freesurface-cells.html)

mrji8011 August 12, 2011 02:12

VOF Coefficient in freesurface cells
 
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.

sail August 12, 2011 13:13

Quote:

Originally Posted by mrji8011 (Post 319831)
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...)

mrji8011 August 13, 2011 20:50

Quote:

Originally Posted by sail (Post 319935)
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

mrji8011 August 18, 2011 00:59

Quote:

Originally Posted by mrji8011 (Post 320010)
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?

sail August 18, 2011 03:50

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.

mrji8011 August 18, 2011 22:08

2 Attachment(s)
Quote:

Originally Posted by sail (Post 320584)
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.

Thanks for replying
Please find the attacheds. I should capture waves in all domain.


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