# UDF for 3d inlet parabolic velocity profile ?

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 June 12, 2011, 07:52 UDF for 3d inlet parabolic velocity profile ? #1 New Member   snowman Join Date: Apr 2011 Posts: 15 Rep Power: 7 hi every body...... i want to use a udf which gives me parabolic velocity profile at inlet. my case is a pipe flow and i have made a model with its face at X-Z face and its length extends in the + ive y direction. can anybody please help me on this ?

 June 17, 2011, 09:28 #2 New Member   Johney Grey Join Date: May 2011 Posts: 6 Rep Power: 7 The UDF manual has a 2D parabolic inlet example. You just need to change that example a little bit.

June 18, 2011, 18:10
#3
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Nuno Gomes
Join Date: May 2009
Location: Portugal
Posts: 39
Rep Power: 9
I try to find in manual, but didnt appear.

How could be when your inlet face is not coincident with the axis?

How it works for the case on picture?for example, for and angle of 50º...

i want to understand how works the x[ND_ND] vector....or array

any help

Plz!!!
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June 19, 2011, 10:43
#4
New Member

Johney Grey
Join Date: May 2011
Posts: 6
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Quote:
 Originally Posted by Dinocrack I try to find in manual, but didnt appear. How could be when your inlet face is not coincident with the axis? How it works for the case on picture?for example, for and angle of 50º... i want to understand how works the x[ND_ND] vector....or array any help Plz!!!
This the manual example:

#include "udf.h"
{
real x[ND_ND]; /* this will hold the position vector */
real y;
face_t f;
{
y = x[1];
F_PROFILE(f, thread, position) = 20. - y*y/(.0745*.0745)*20.;
}
}

For 2D case, the X[ND_ND] has X[0] for axis x and X[1] for axis y.
For 3D case, the X[ND_ND] has X[0] for axis x, X[1] for axis y and X[2] for axis z.

If your inlet is not coincident with the axis you need to calculate the distance between certain point on the inlet surface and inlet center.

 June 22, 2011, 11:27 #5 Member   Nuno Gomes Join Date: May 2009 Location: Portugal Posts: 39 Rep Power: 9 thank for your reply. So you telling me that we need to know the position point of inlet center?

 June 23, 2011, 08:28 #6 New Member   Johney Grey Join Date: May 2011 Posts: 6 Rep Power: 7 You need coordinate transformation at first then you can process it as the inlet face coincident with the axis. wiki page for coordinate transformation: http://en.wikipedia.org/wiki/Coordin...dinate_systems

 June 23, 2011, 16:40 #7 Member   Nuno Gomes Join Date: May 2009 Location: Portugal Posts: 39 Rep Power: 9 thank again for your answer. I already solve the problem. Was a geometric construction of the reactor. But to solve this kind of UDF's we need to rotate the axis and then see see the coordinates. Thank again

December 6, 2015, 08:36
#8
New Member

Saba Golshaahi Sumesaraayi
Join Date: Nov 2015
Posts: 1
Rep Power: 0
Quote:
 Originally Posted by Dinocrack thank again for your answer. I already solve the problem. Was a geometric construction of the reactor. But to solve this kind of UDF's we need to rotate the axis and then see see the coordinates. Thank again
Hi Dino, Actually it is about 7 years after you post but I exactly need the UDF for the parabolic laminar velocity inlet in an Inclined tube exactly as yours probably only with difference in slope! As I am really in hurry, if by any chance you have the UDF code for it, and it is OK for you to give me the code that I can modify it, it would be awesome! Unfortunately I have only a simple Experience with UDF.

 December 7, 2015, 08:52 #9 Senior Member   Bruno Join Date: Mar 2009 Location: Brazil Posts: 272 Rep Power: 13 If you're in a hurry and you have no experience in UDF, what you should do instead is write a profile for the velocity based on (x,y,z) positions and use that as a boundary condition. Fluent has a few tutorials explaining how to use profiles. The documentation will also help you. Cheers

March 24, 2016, 06:36
#10
New Member

Yu Lu
Join Date: Jul 2015
Posts: 14
Rep Power: 2
Quote:
 Originally Posted by brunoc If you're in a hurry and you have no experience in UDF, what you should do instead is write a profile for the velocity based on (x,y,z) positions and use that as a boundary condition. Fluent has a few tutorials explaining how to use profiles. The documentation will also help you. Cheers
Hi Bruno, sorry to dig this ancient post, I actually encountered this problem that I want a 3D parabolic velocity inlet but I don't have any experience using UDF, can you please where to find the the tutorials you mentioned about writing velocity profile based on positions ?Thanks a lot.

 March 28, 2016, 15:00 #11 Senior Member   Bruno Join Date: Mar 2009 Location: Brazil Posts: 272 Rep Power: 13 Hi yulu, Visit the ANSYS Customer Portal and search for "fluent udf tutorial" in there.

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