MANUAL Fluent 5

Volume of Fluid : Two Phases Flow

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The aim of this version is to describe in more details the way to use the Volume of Fluid Model with Fluent.

First Steps :

Let's view the definition of the Operating conditions : Define ->Operating Conditions :

In our case, the study was axisymmetric (Define->Model->Solver and click 2D-Axisymmetric), and Fluent accepts only an axis oriented as the X-axis, that's why the Gravitational Acceleration is on X. When doing an axisymmetric study, you have to define your axis, and if your mesh has been made with PRE-BFC (which does not have axis zone), you have to change your symmetry boundary condition into an axis (Define->Boundary Conditions).
Note that you have also to click Specified Operating Density.

Our study is to compute a bubble of air in the gravity champ in a column of water. So to enable the surface tension, you have to specified it in the Multiphase Model Panel (cf Version 1 : Define->Model->Multiphase Model) :


You can test the different VOF Scheme, but for our study the Geo-Reconstruct one was recommended.
You can also try to Solve VOF Every Iteration, but it is only recommended if under-relaxation factors are well set.
Then you have to specify the solution's parameters Solve->Control->Solution :


Defining a Bubble :

As it is explain in the Version 1 of the VOF with Fluent Manuel, you have to Adapt->Region, click circle, choose center coordinates and the radius of your bubble :

Then click on Mark, on Manage... ->Display if you want to see cells to be adapted, and on Adapt. Repeat the sequence Mark/Adapt, until your bubble is a circle (you can see it with Manage...->Display, after a Mark action). Here is the bubble obtain after some Mark/Adapt sequences :

Then you can follow the Version 1's explaination to initialize the two phases.