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Assigning values for outlet boundary from its adjacent cell

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Old   July 11, 2013, 12:08
Red face Assigning values for outlet boundary from its adjacent cell
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Ali nabavi
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Hello,

I am very new to the world of UDF ( Mostly 3 days!). I want to write a UDF for my outlet boundary condition (pressure outlet) to get its value from its neighbor (adjacent cell).

Actually I am struggling to how can I get the info from the adjacent cell and then assign it to the boundary cell.

I know it is very was but I am struggling for a couple of days and still no result.
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Old   July 11, 2013, 21:54
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Technically it is not hard to do this. But physically are you seeking for the far field or outflow b.c.?
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Old   July 11, 2013, 22:05
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Nara Shikamaru
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I was looking a way to fix velocities in adjacent cells of a boundary (which is not the right thing to do by the way). Take a look at this macros, you might be able to do what you want to do with these.

1. Use Lookup_Thread to find the face thread pointer to the boundary.
2. Use begin_f_loop to loop over the faces of the face thread
3. Use F_C0 and F_C1 to find the cell threads of the adjacent cells of the face
4. F_C0_THREAD and F_C1_THREAD will give you the thread pointer to the adjacent cells
5. use the cell the thread pointer to copy the values from those cells

---do what ever you want after that with those.

Hope it helps.
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Old   July 11, 2013, 22:05
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Ali nabavi
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Thank you for your fast reply...

Actually i want to use it for pressure outlet B.C.
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Old   July 11, 2013, 22:19
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Quote:
Originally Posted by shikamaru View Post
I was looking a way to fix velocities in adjacent cells of a boundary (which is not the right thing to do by the way). Take a look at this macros, you might be able to do what you want to do with these.

1. Use Lookup_Thread to find the face thread pointer to the boundary.
2. Use begin_f_loop to loop over the faces of the face thread
3. Use F_C0 and F_C1 to find the cell threads of the adjacent cells of the face
4. F_C0_THREAD and F_C1_THREAD will give you the thread pointer to the cells
5. use the cell the thread pointer to copy the values from those cells

---do what ever you want after that with those.

Hope it helps.
Thank you so much for response!. To clarify your answer:

You mean in fluent find the zone ID and using Lookup_thread to find t of boundary faces. So until here I will have the t of boundary faces.
Then using begin_f_loop start my loop.
Next with F_c0 and F_c1 what will I get? Imagine I have a horizontal pipe which the fluid is flowing from the left to the right. If I use those F_c0 and F_c1 what will I get as the face is on outlet boundary so there is no C1 then?
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Old   July 12, 2013, 01:06
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Read the UDF Manual: Chapter 3: Additional Macros for Writing UDFs and look for this macros

in V13, page 220 will clarify what you want to know.

Out of Curiosity, why do you want to look at the pressure of the adjacent cells of the outlet?
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Old   July 12, 2013, 05:09
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Ali nabavi
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Quote:
Originally Posted by shikamaru View Post
Read the UDF Manual: Chapter 3: Additional Macros for Writing UDFs and look for this macros

in V13, page 220 will clarify what you want to know.

Out of Curiosity, why do you want to look at the pressure of the adjacent cells of the outlet?
Thank you very much. I will take a look and will let you know about the result. I am modelling multiphase flow at the outlet boundary when all three phases are exiting the domain because our consider pressure outlet with a constant pressure as a default, there will be some disorders in my flow and it does not allow my phases to exist as easily as they were passing through the micro channel I tried outflow boundary but got worst result in this way to adjust on minimised the difference of outlet pressure with those three phases I want to condier the adjacent cell pressure for outlet and make my mesh super fine.

Hope you have some alternative remedy...
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Old   July 12, 2013, 15:11
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I am doing something similar for multiphase flow. I am using VOF, check msg.
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