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-   -   Error in VOF model FLUENT 14.5.7‏ (https://www.cfd-online.com/Forums/fluent/126025-error-vof-model-fluent-14-5-7-a.html)

Volumeoffluid November 6, 2013 09:56

Error in VOF model FLUENT 14.5.7‏
 
Hi all,
when i use VOF model my programm cannot recognize the two different phases. When i change one phase (air) automatically changing the other (water)...I don't understand why this happen.
Specially....there was this message: Unassigned interface zone detected for interface xx
I should define this mesh interface, but i dont know how exactly i can do this...
I adjusted some options in Meshing and Designmodeler but the same warning again.
I can send you photos of my project.

Thank you in advance!

smhosseini November 18, 2013 04:24

Hi Dimitris,
If you explain more about your problem and your boundary condition, I can help you.

Volumeoffluid November 21, 2013 12:21

Quote:

Originally Posted by smhosseini (Post 462349)
Hi Dimitris,
If you explain more about your problem and your boundary condition, I can help you.

Hi smhosseini,
thank you for your replay!
So do you want to send you a picture of my geometry to your email or skype
my email is jimromanas@hotmail.com
Best regards
Dimitris

smhosseini November 21, 2013 16:27

ok, I'll send you my email address.

Zaktatir November 21, 2013 17:04

Are you using non conformal meshes? That sounds that you need to define an interface since some boundaries are treated as interfaces.

Check the types of the BC's

kad November 21, 2013 18:48

Quote:

Originally Posted by Volumeoffluid (Post 460844)
Hi all,
when i use VOF model my programm cannot recognize the two different phases. When i change one phase (air) automatically changing the other (water)...I don't understand why this happen.

Does this happen when you try to set up the BCs? If yes, this is the usual behaviour in fluent. When you pick phase1 at inlet, Fluent switches automatically the outlet to phase 1, too. This does not mean that there is only phase 1 at the outlet. It's because you have to define BCs for each phase and mixture. What exactly has to be defined can be found in the manuals. Often pase 2 does not require any input. It is a little confusing in the beginning.

Of course it is also important to patch your volume fraction right. Have look at the tutorials for this. If you are unsure about your setup just run a few iterations and check contour plot for volume fraction. This also helps little bit for understanding. You can even do it right after patching or initialization.

Is there a boundary called "interface" in your mesh? I think fluent tries to assign BCs to mesh boundaries that have obvious names like inlet, outlet or interface when importing mesh. If yes this is normal, because the interface is not defined yet. This can be done how it is shown in the tutorials e.g. sliding mesh tutorials. Otherwise just change the kind of BC to what you want. You did not make really clear if you want an interface in your mesh or if this an "accident".

Volumeoffluid November 22, 2013 09:21

Quote:

Originally Posted by kad (Post 463012)
Does this happen when you try to set up the BCs? If yes, this is the usual behaviour in fluent. When you pick phase1 at inlet, Fluent switches automatically the outlet to phase 1, too. This does not mean that there is only phase 1 at the outlet. It's because you have to define BCs for each phase and mixture. What exactly has to be defined can be found in the manuals. Often pase 2 does not require any input. It is a little confusing in the beginning.

Of course it is also important to patch your volume fraction right. Have look at the tutorials for this. If you are unsure about your setup just run a few iterations and check contour plot for volume fraction. This also helps little bit for understanding. You can even do it right after patching or initialization.

Is there a boundary called "interface" in your mesh? I think fluent tries to assign BCs to mesh boundaries that have obvious names like inlet, outlet or interface when importing mesh. If yes this is normal, because the interface is not defined yet. This can be done how it is shown in the tutorials e.g. sliding mesh tutorials. Otherwise just change the kind of BC to what you want. You did not make really clear if you want an interface in your mesh or if this an "accident".

Thank you a lot for your answer!
So my Fluent recognize one domain...no 2 domains to specify the two fluids.
And for this reason it cannot accept the two phases and change it the one automatically when i change the other.
I can send you my geom to take a look if you have time...
my email is jimromanas@hotmail.com
If i face up this problem...i ll set the problem BCs as the tutorials...
Thank you in advance!

thermal energy March 14, 2014 12:55

Hello dear friends,

I try to simulate melting process using VOF model. Pcm is solid phase initialy. Upper part of the solid there is air. They do not mix eachother. Natural convection is active. My primary phase air, secondary phase is pcm (phase change material). I have some questions to be sure about my model.

First, I do not define interface between air and pcm. Mean, There are 3 cell zone: air, fin ,pcm but I do not create name selection for this interface in meshing. Is it ok?

Initial condition of Wholesystem temperature is 293K, but air temp is 300K. how to set air temp ?

For cell zone condition, all cell zone (air, pcm, fin ) show mixture. Also for example, if I change pcm to phase2, all of cell zone change to phase 2

Only for secondary phase (pcm), I patch within fluent by adapt-region-mark then patch. Ok? Value of volume fraction should be 1 or 0 while patching?? I am confused. Initialy pcm is solid.

For initial values phase-2 volume fraction is 0. Ok?

I did some iteration for a short time to check model. For results, in graphics-countors I can not see total temperature for phase 1 and 2 only entalphy values I see for phase1 and 2.

Also countors of solidification/melting it shows only mixture. Mixture show what?

Any interaction should I use like surface tension etc.

Thanks for your help.

shmurali July 7, 2014 01:55

Hey I am also facing the same prob, did you find the what is the solution for it ??.....kindly request your help

6863523 August 21, 2014 22:00

Hi guys,
I wonder if you are familiar with the wick-vapor interface aere alculation? I am working on the phase change(liquid water-vapor evaporation; vapor-liquid water condensation), water flows inside a porous wick and evaporates on the surface of the wick; vapor flows in the vapor chamber and condenses on another surface of the wick; the wick surrounds the vapor chamber.
I wonder if the VOF model in FLUENT could simulate the phase change. As after some iteration, the phase fraction would change in the whole domain, especially near the interface. After a long time, the phenomenon would be quite strange, all of the water would change into vapor or the vapor would become into liquid water. I only adjusted the accomodation coefficient in the EVAPORATION-CONDENSATION model.
Any reply would be appreciated. My emial: 815719752@qq.com
Regards,
Bill


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