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-   -   vof and small bubbles (http://www.cfd-online.com/Forums/fluent/32535-vof-small-bubbles.html)

frankastell November 17, 2003 13:22

vof and small bubbles
 
hi everyone, i'm working with VOF to simulate the rise of air bubbles in water, but with small bubbles (d<2mm) it doesn't function. with the bigger ones every thing is ok. i try with and without surface tension. do you know if VOF has problems with small particles? thanks a lot.

Easycad November 17, 2003 15:58

Re: vof and small bubbles
 
Hi

Why dont you use DPM? I think it is more appropriate

mateus November 18, 2003 07:35

Re: vof and small bubbles
 
Hi!

Grid resolution might be a problem...do you have fine enough grid for so small particles? Maybe it's really better to work with DPM - it depends what you're interested in...

Regards

MATEUS

frankastell November 18, 2003 07:52

Re: vof and small bubbles
 
thank you for your attention!!!

i'm testing VOF for my thesis. i'm simulating bubbles with different diameters but always with 300 cells/bubble. i tried to simulate the small ones also with 900 cells/bubble but i didn't see any change in the rise velocity. the problem is that this kind of bubble accelerates just until 6 cm/s and it assumes a non spherical shape: in the reality, i.e. a 1 mm bubble is spherical and it has a terminal velocity near 30 cm/s. any idea? do i have to conclude that VOF isn't able to predict the comportment of this kind of particles? thanks a lot.

regards.

ROOZBEH November 19, 2003 03:10

Re: vof and small bubbles
 
Hi;

Dear mateus;

Whould you pay attention to my new message in this page!

Recently the new version of fluent is avalable for me. But I am working with it with no success! What settings are required in this new version.(modification pressure limit?_modification of termination criteria?_ ....)

richard December 11, 2003 11:28

Re: vof and small bubbles
 
hi, frankastell, what is the mean of 300cells/bubbles?is there 300 cells in a bubble?and what is the mean of terminal velocity? I don't catch what you say, would you please tell me more clearly?


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