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Old   July 13, 2010, 05:28
Default 2 inlets, 2 UDF
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plz i need an urgent help.
i have to inject oil into water.
the problem that water must have a specific profile of velocity so i have to introduce a UDF. and same for the oil.
so i don't know how to define 2 UDF and interpret them in each inlet.
plz help
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Old   December 12, 2010, 14:26
Question UDF needed too
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I too need udf function for a fully developed velocity profile at inlet in vertical channel . As i have never worked on Fluent i dont know how udf
have to write is it exactly the same code as in FORTRAN or C as i know
both well but udf i dont know
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Old   December 12, 2010, 14:54
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UDF's are User Defined Functions

They are typically written in C, but can be written in Fortran. Fluent has a C interpreter built in, so you don't need one unless aspects of the calculation (specific Fluent calls, speed of calculation, etc) require compilation.

To impose a fully developed profile at a wall, you must loop over all faces of the wall and set the velocity magnitude (or, perhaps, a vector component) equal to the velocity you obtain from fully developed flow.

In the code below, I assume the following:
1) Fully developed laminar flow
2) 2-D flow in the x-direction
3) An inlet face which extends from 0.5 to -0.5 in the y-direction
4) A maximum centerline velocity of 10

#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)
      y = x[1];
      F_PROFILE(f, thread, position) = 10.-10.*(y*y/(0.5*0.5));
  end_f_loop(f, thread)
I haven't tested it, but it should function OK with few, if any, changes. I don't know which direction you've specified as vertical, so you'll need to adapt a few things in the code above to fit your application.

Go here:
for more information on UDFs.

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Old   December 13, 2010, 03:04
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many thanks to ComputerGuy for you help and code I will try to learn and do whatever is needed furthermore.
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