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UDF for 3d inlet parabolic velocity profile ?

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Old   June 12, 2011, 07:52
Question UDF for 3d inlet parabolic velocity profile ?
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snowman
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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 ?
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Old   June 17, 2011, 09:28
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Johney Grey
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The UDF manual has a 2D parabolic inlet example. You just need to change that example a little bit.
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Old   June 18, 2011, 18:10
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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 50...

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

any help

Plz!!!
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Old   June 19, 2011, 10:43
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Quote:
Originally Posted by Dinocrack View Post
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 50...

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

any help

Plz!!!
This the manual example:

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


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.
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Old   June 22, 2011, 11:27
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thank for your reply. So you telling me that we need to know the position point of inlet center?
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Old   June 23, 2011, 08:28
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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
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Old   June 23, 2011, 16:40
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Nuno Gomes
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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
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Old   December 6, 2015, 08:36
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Saba Golshaahi Sumesaraayi
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Quote:
Originally Posted by Dinocrack View Post
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.

Thanks in advance
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Old   December 7, 2015, 08:52
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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
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