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.

I dun know!!!!!!

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.

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?

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?

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.

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

Sincerely, Jinwook

Thanks for your feecback, I try to use implicit scheme. It works!

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

Yap, it is two phase stage.

The problem solved as I follow what Lafferty suggested.

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.

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

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