# Initialising VOF model

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November 25, 2010, 05:20
Initialising VOF model
#1
New Member

Join Date: Nov 2010
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Hi, does anyone know how to initialise the VOF model in STAR-CCM+ so that I can specify a particular area of the grid to one phase, and have the rest as the other phase.

It's the analagous case of the "adapt -> region -> mark cells" and then "patch" commands in FLUENT. I've attached an image of how it looks in FLUENT if I wasn't clear enough.

Any help at all would be appreciated
Ste
Attached Images
 example.jpg (22.9 KB, 130 views)

November 26, 2010, 03:04
Initializing VOF
#2
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Christian Jungreuthmayer
Join Date: Mar 2009
Posts: 9
Rep Power: 17
Hi Ste,

You will get an "Initial Conditions" branch in the "Region"-tree. There you can specify pressure, temperature, velocity, ... and also volume fraction. Usually, I use field functions to initialize the volume fraction. There you can do all sort of tricks, e. g. specify areas using the "Position" field function. For example:
(\$\$Position[0] < 0.04 && \$\$Position[1] > 0.05 && \$\$Position[1] < 3.05) ? 1.0 : 0.0

Christian
Attached Images
 init_vof_1.jpg (29.2 KB, 118 views) init_vof_2.jpg (29.3 KB, 106 views)

 October 11, 2011, 18:49 Slug flow Initial Boundary Conditions #3 New Member   Leonardo Join Date: Oct 2011 Posts: 4 Rep Power: 14 Hi, I actually have kind of the same problem since it's difficult even to have the stratified flow when running constant velocity fraction. How do you come up with the equation? Where can I get information in specifying the equation to define? Leonardo

October 15, 2011, 08:33
#4
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Join Date: Oct 2009
Location: Germany
Posts: 636
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Quote:
 Originally Posted by leonard Where can I get information in specifying the equation to define?
Have a look in the field function programming reference, there you will find the needed information.
The equation is just an if-clause.
For example if the coordinate in X-direction of a vertice of a cell (\$\$position[0]) is smaller than 0.04, the result should be 1. If not, the result should be 0.
Define this as initialisation field function and every cell will get the volume fraction according to this if-clause. That's all.

The example from Tron is just a combination of several if-clauses for different directions.

 October 15, 2011, 08:37 #5 Senior Member   Join Date: Oct 2009 Location: Germany Posts: 636 Rep Power: 21 For complicated shapes it might be worth to create a cell set as you can pick every single cell you want to include to this set. When a cell set is created, there will be a new field function with the name of the cell set which is 1 for cells contained in the set and 0 for all other cells.

 October 16, 2011, 18:55 Stratified flow 50% water 50 %air #6 New Member   Leonardo Join Date: Oct 2011 Posts: 4 Rep Power: 14 Thank you very much for your help. I am getting the stratified flow. My model is a pipe with bends, so the idea is to have slug flow in the next sections of the pipe. I am running different cases to check if it forms. In case of any doubts I might ask for help. Thanks again.

 October 16, 2011, 21:54 sine function user defined field function #7 New Member   Leonardo Join Date: Oct 2011 Posts: 4 Rep Power: 14 Any of you know how to create a field function with the following condition? My CFD consultant told me to set that field function to be able to form slug flow. if sin(wt)) >0; 1:0 I tried to set it first similar to the menu: (sin(\$x)>0)?1:0), but I still need to define the x, which in this case would be wt. As you know w=2pif or 2pi/T, but how can I define this as a field function? Thank you

 October 20, 2011, 08:14 #8 Senior Member   Join Date: Oct 2009 Location: Germany Posts: 636 Rep Power: 21 (sin(omega*\$Time)>0)?1:0) Omega is a constant value and can here be given directly as a number.

 October 24, 2011, 18:36 #9 New Member   Leonardo Join Date: Oct 2011 Posts: 4 Rep Power: 14 Thanks for your help. It was really helpful.

October 24, 2011, 23:24
VOF wave
#10
New Member

yanmei
Join Date: May 2011
Posts: 4
Rep Power: 15
Hi, need helps. I am seting the VOF wave in a flume, but i don't know why the result isn't correct. It should be regular wave propagation.
The wave should propagate from the left side to the right.

please see the attachment,
any one knows, and tell me why. Thanks.
Attached Images
 star_ccm.jpg (68.8 KB, 80 views)

 October 14, 2015, 06:45 Initialise VOF using field function to Cell Set #11 New Member   Rixson Join Date: Jul 2015 Posts: 1 Rep Power: 0 how to initialise VOF using field function to cell set created in starccm+ ?

 Tags initialization, initiallisation, regions, slug flow, vof

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