# Half parabolic profile for the velocity inlet

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 July 19, 2012, 09:27 Half parabolic profile for the velocity inlet #1 New Member   adele Join Date: Apr 2012 Location: France Posts: 7 Rep Power: 6 Hi, I'm trying to model the heat transfer in a shell and tube heat exchanger and I'm using Fluent for this. To simplify the problem, and to reduce the time calculation, I cut the geometry in 6 in the length direction, and study just a 6th of the geometry. That is why my velocity inlet pipes (the small ones) are cut either in 2 or in 6 equal parts. You can see a picture of the geometry here. However I want to insert a parabolic profile with a UDF in the 3 cut pipes by respecting the center of the paraboloid and the cut geometry. My questions are: - is it possible to define the three inlet faces of the pipes as three different velocity inlet faces, and to define a parabolic profile for each one? Or do I have to group the faces and write only one UDF for the velocity profile? - Is it possible to insert a parabolic profile even if the tube is cut? I mean, without changing anything in the C code. If yes, how to define a different coordinate system origin for each one? I read somewhere that it's better when the system origin in the UDF is also the system origin in Fluent Thank you in advance for the help! Adele

July 19, 2012, 09:50
#2
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Alex
Join Date: Jun 2012
Location: Germany
Posts: 1,282
Rep Power: 22
Quote:
 is it possible to define the three inlet faces of the pipes as three different velocity inlet faces
Yes it is. This is the way to do it.

Quote:
 and to define a parabolic profile for each one
If you know the coordinates of the center of the small pipes, this should be quite easy. You just need to offset the velocity profiles in your UDF.
Quote:
 Is it possible to insert a parabolic profile even if the tube is cut
No problem. In the UDF, you read the face centroids of all the cells adjacent to the inlet. If some o fthe faces are missing because the geometry was cut, the loop over the faces will just finish earlier.
Quote:
 If yes, how to define a different coordinate system origin for each one?
Like I said, I wouldn't use different coordinate systems. I would offset the velocity profiles instead.

 July 19, 2012, 10:26 Thank you! #3 New Member   adele Join Date: Apr 2012 Location: France Posts: 7 Rep Power: 6 Thank you so much for the quick and efficient reply! I try this solution as soon as possible and if I have problems, I will come back to you! Adele

 July 19, 2012, 11:31 offset velocity #4 New Member   adele Join Date: Apr 2012 Location: France Posts: 7 Rep Power: 6 One more question: I made a traditional UDF of a paraboloid profile for the central pipe, whose center corresponds to the coordinates system origin. I will do the same for the other pipes, but how do I take into account the offset the velocity? Is there a special code for this, or do I have to adapt my equation in function of the x position? thanks in advance

July 19, 2012, 11:43
#5
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Patrick
Join Date: Apr 2012
Posts: 28
Rep Power: 6
Quote:
 Originally Posted by adele One more question: I made a traditional UDF of a paraboloid profile for the central pipe, whose center corresponds to the coordinates system origin. I will do the same for the other pipes, but how do I take into account the offset the velocity? Is there a special code for this, or do I have to adapt my equation in function of the x position? thanks in advance
You could use a conditional statement. ie

if x<rangeXupper1 and x>rangeXlower1 and y<rangeYupper1 and y>rangeYlower1 then

velocity=... (function for inlet 1)

elseif x<rangeXupper2 and x>rangeXlower2 and y<rangeYupper2 and y>rangeYlower2 then

velocity=.... (function for inlet 2)

Where rangeX... are the bounds for the x and y co-ordinates of each inlet.

Or yes just adapt the equation which is perhaps a simpler way of doing it, this way allows you to change the equation and position individually though, which might be quicker if you need to change either of them.

 Tags 3d-geometry, cut pipes, udf, velocity profile

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