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November 25, 2010, 06:20 
Initialising VOF model

#1 
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Hi, does anyone know how to initialise the VOF model in STARCCM+ 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 

November 26, 2010, 04:04 
Initializing VOF

#2 
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Christian Jungreuthmayer
Join Date: Mar 2009
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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 

October 11, 2011, 18:49 
Slug flow Initial Boundary Conditions

#3 
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Leonardo
Join Date: Oct 2011
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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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Quote:
The equation is just an ifclause. For example if the coordinate in Xdirection 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 ifclause. That's all. The example from Tron is just a combination of several ifclauses for different directions. 

October 15, 2011, 08:37 

#5 
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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 
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Leonardo
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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 
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Leonardo
Join Date: Oct 2011
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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 
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(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 
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Leonardo
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Thanks for your help. It was really helpful.


October 24, 2011, 23:24 
VOF wave

#10 
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yanmei
Join Date: May 2011
Posts: 4
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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. 

Tags 
initialization, initiallisation, regions, slug flow, vof 
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