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-   -   Initialising VOF model (http://www.cfd-online.com/Forums/star-ccm/82404-initialising-vof-model.html)

Ste November 25, 2010 06:20

Initialising VOF model
 
1 Attachment(s)
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

Tron November 26, 2010 04:04

Initializing VOF
 
2 Attachment(s)
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

leonard October 11, 2011 18:49

Slug flow Initial Boundary Conditions
 
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

abdul099 October 15, 2011 08:33

Quote:

Originally Posted by leonard (Post 327557)
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.

abdul099 October 15, 2011 08:37

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.

leonard October 16, 2011 18:55

Stratified flow 50% water 50 %air
 
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.

leonard October 16, 2011 21:54

sine function user defined field function
 
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

abdul099 October 20, 2011 08:14

(sin(omega*$Time)>0)?1:0)

Omega is a constant value and can here be given directly as a number.

leonard October 24, 2011 18:36

Thanks for your help. It was really helpful.

ymz_0308 October 24, 2011 23:24

VOF wave
 
1 Attachment(s)
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.


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