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-   -   Doubt with fluent (http://www.cfd-online.com/Forums/fluent/27997-doubt-fluent.html)

David November 2, 2000 11:34

Doubt with fluent
 
I am using fluent to simulate a multiphase fluid which is air and water through a pipe. The model I used is VOF. However, when I begin to iterate, the air phase wont appear, I try it many times with different specification but still fail. I would like what probably wrong with my simulating.

ABC November 2, 2000 12:00

Re: Doubt with fluent
 
I dun know!!!!!!

Clinton Lafferty November 2, 2000 14:09

Re: Doubt with fluent
 
Just to check: What value are you using to intializing the volume fraction. Also, are you patching the same value to entire domain or certain zones.

David November 2, 2000 21:45

Re: Doubt with fluent
 
Value of air volume fraction is 0.9. Yes, I have patched the value to the enire volume. By the way, how does it related to the iteration?

And alsohere is the properties which I used to initializing:

Solver: segregated

Formulation: implicit

Time: steady

Space: 3D

velocity: absolute

Materials: water

air

Models: energy (enabled)

viscous: k-epsilon

multiphase- VOF (primary phase is water and secondary phase is air)

Is there any other properties which will affect the result?


David November 2, 2000 21:48

Re: Doubt with fluent
 
Value of air volume fraction is 0.9. Yes, I have patched the value to the enire volume. By the way, how does it related to the iteration?

And alsohere is the properties which I used to initializing:

Solver: segregated

Formulation: implicit

Time: steady

Space: 3D

velocity: absolute

Materials: water

air

Models: energy (enabled)

viscous: k-epsilon

multiphase- VOF (primary phase is water and secondary phase is air)

Is there any other properties that will affect the result?


Clinton Lafferty November 2, 2000 23:26

Re: Doubt with fluent
 
Couple of points to investigate further - (I have only been using the VOF model for a couple of months):

1) Steady Flow Simulations - VOF tends to work better under transient simulations; however, selecting the implicit scheme instead of geo-reconstruct or Euler Explict allows steady flow simulations.

2) Solving the Energy Equation - according to the manual this is not allowed.

Keep in mind, the solution will be greater effected by the grid resolution, especially in the water-air interface regions.

Jin-Wook LEE November 3, 2000 06:09

Re: Doubt with fluent
 
VOF model is to find interface between two phases. It is not aimed to solve mixed state. How about your case ?

Sincerely, Jinwook


David November 4, 2000 21:47

Re: Doubt with fluent
 
Thanks for your feecback, I try to use implicit scheme. It works!

Just to ask: when to use implicit, explicit and geo-reconstruc?

David November 4, 2000 21:53

Re: Doubt with fluent
 
Yap, it is two phase stage.

The problem solved as I follow what Lafferty suggested.

Clinton Lafferty November 5, 2000 19:54

Re: Doubt with fluent
 
As with most everything in fluent it depends on the flow simulation. I cannot tell you any more than what is the manuals or under the help menu.

Jin-Wook LEE November 5, 2000 20:48

Re: Doubt with fluent
 
I do not know what is Lafferty's suggestion. I mean that VOF can not solve two phase flow of LOCALLY mixed air and water. It can solve two phase flow with interface between air and water, such as water filled spinning cup which has interface with air on the free surface.

Sincerely, Jinwook


Adel Ataki November 14, 2000 15:32

Re: Doubt with fluent
 
hallo David, can I get some information about your domain, I mean inlet and outlet of the pipe and pressure reference you'v determined for your iterations and the kind of creterions you'v used to know the availability of your simulations results. it well help me a lot with a lot of thanks Ataki


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