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Transient movement of fluid front at outlet of a water tap

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Old   June 8, 2010, 03:10
Default Transient movement of fluid front at outlet rim of a water tap
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Hi there,

I would like to model somekind of water tap. I am especially interested in the conditions at the outlet. If the wall is modelled as a wall and not just as a plane I will get adhesive forces. These forces will cause the fluid to attach (see picture). In case of a transient laminar calculation the front of the fluid, where fluid, solid, and gas meet will move until all forces are in balance. The problem I am faced with is the fact of no slip conditions at the wall. How would I be able to allow the movement of the front but still conform the boco of zero velocity? I think I would have to model microscopic forces. Is there another way than applying a multiscale modelling?

Any help would be much appreciated
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Last edited by mannobot; June 8, 2010 at 04:08.
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Old   June 16, 2010, 04:57
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Sorry I'm a bit late.

May be this could help you.


http://www.google.com/url?sa=t&sourc...4XZb950QQyZ21g


It's a tutorial from Hassan_Hemida_VOF
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Old   June 16, 2010, 12:40
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Hi Stefan,

thank you very much for your reply. I will read the material and try to understand. Maybe we can stay in touch in case of arising problems.

Sincerely

mannobot
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Old   June 16, 2010, 17:22
Default liquid front
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Use commercial or own CFD multiphase code: run VOF model as suggested. Its a matter of minutes before you see results !

For good understanding in the near wall region at the exit, refine the mesh well and input proper surface tension values. You will get curvatures (if you have resolved the region well) of the liquid attachign to the walls.

No microscopic effects needed: CFD modeling has already averaged them for your convinience.

Thanks,

/CFDtoy

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Originally Posted by mannobot View Post
Hi there,

I would like to model somekind of water tap. I am especially interested in the conditions at the outlet. If the wall is modelled as a wall and not just as a plane I will get adhesive forces. These forces will cause the fluid to attach (see picture). In case of a transient laminar calculation the front of the fluid, where fluid, solid, and gas meet will move until all forces are in balance. The problem I am faced with is the fact of no slip conditions at the wall. How would I be able to allow the movement of the front but still conform the boco of zero velocity? I think I would have to model microscopic forces. Is there another way than applying a multiscale modelling?

Any help would be much appreciated
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Old   June 17, 2010, 03:23
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Dear CFDtoy,

so you think I will get a moving front? These must be a result of capillary forces. I thought the no slip condition at the wall has to cause problems. That is what I was told.

Sincerely

Mannobot
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Old   June 17, 2010, 16:24
Default water front
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well yes...here are the input required

1. inlet velocity of the tap water - if the velocity is too low (rayleigh regime) we are looking at drops. Now, if the capillary forces are high (surface tension effects) and at the same time inlet velocity is too low...drop just sticks there...does not "drop". This is probably what you want to see??

if so, check your inlet velocity: there are tons of literature on the breakup regimes...rayleigh, first wind induced, second, turbulent breakup etc

with this inlet velocity, you have a Re and for a given liquid, the weber number ..these 2 will tell you waht kind of regime you are in ..and in theory,

if the reynolds number increases and the force term becomes > surface tension force, the droplet will move downstream..if not ..it will stick there..


hope this helps.

regards,

/CFDtoy


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Originally Posted by mannobot View Post
Dear CFDtoy,

so you think I will get a moving front? These must be a result of capillary forces. I thought the no slip condition at the wall has to cause problems. That is what I was told.

Sincerely

Mannobot
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Old   June 18, 2010, 03:40
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Dear CDFtoy,

thank you for your immediate response. Please do excuse the lack of crarity within my explainations.
I added to possible scenarios. Both are depending on the fluid properties imaginable. I want to observe wether or not the contact line does wet the outlet-wall and how far it does move. I marked the point I do define as contact line. I hope this explaination helps to clarify my problem. I know the contact angle is not displayed physical correct but I think it will work.

Thank you so much for your time.

Sincerely

Mannobot
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File Type: jpg Scenario_2.jpg (55.8 KB, 4 views)
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