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Old   August 22, 2011, 02:51
Question UDF in Cylindrical Coordinate
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Masoud Hassani
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Hi guys,
I am a newbie in UDF world and I need some help for a simple UDF problem.
I have a 3d turbo setup and i need to have tangential velocity profile in inlet as a function of "r" in cylindrical coordinate. I had no idea about C programing and UDF so I used Fluent sample for inlet boundary and changed it to this:

#include "udf.h"
real x[ND_ND];
real y[ND_ND];
real xx;
real yy;
face_t f;

begin_f_loop(f,thread) /* loops over all faces in the thread passed
in the DEFINE macro argument */
yy = y[1];
xx = x[1];

F_PROFILE(f,thread,index) = 0.00002*(xx*xx+yy*yy)*1000000-0.028*sqrt(xx*xx+yy*yy)*1000+11.565;

Clearly it did not work because I did not know what I was doing!!! please helpme to change this UDF to give me velocity in cylindrical coordinate as "0.00002*r^2*1000000-0.028*r*1000+11.565" where "r" is radial distance from 0,0,0
Thank you

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Old   August 22, 2011, 05:46
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If I am not mistaken the;-


Should give you the x,y,z coordinates for the cell such as;-
x[0] = x
x[1] = y
x[2] = z
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Old   August 22, 2011, 06:43
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Masoud Hassani
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Thank you so much! It is so easy
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Old   April 18, 2012, 06:55
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Aydın Dönmez
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i also have to define a parabolic tangential profile but the velocity values computed by the udf does not match with the real values. help please!

#include "udf.h"
real x[ND_ND]; /* this will hold the position vector */
real r,R,omega;
face_t f;

F_PROFILE(f,t,i) = (omega*R*R/r)*(1-exp(-r*r/R*R));
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cylindrical, inlet, udf

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