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ChristineL February 16, 2010 16:11

UDF inlet velocity profile mismatch with Fluent
I am prescribing a velocity profile at the inlet of my mesh. Fluent compiles the c file fine and the solution does converge. However, the velocity profile that I am inputting is a parabola and Fluent does not plot the correct shape of my profile at the inlet. My UDF code is show below. My y coordinates start at zero and goes to 0.0093 m.
Any ideas on why Fluent is not interpreting the correct velocity profile would be appreciated.

#include "udf.h"
#include "mem.h"

/** Parameter Constants **/

#define wallspeed 7.0711

#define finalheight 0.0093

#define height 0.001

/***************** Inlet Velocity Profile in Slot *****************/
DEFINE_PROFILE(inlet_velocity_profile,thread,posit ion)
real x[ND_ND];
real y;
face_t f;

y = fabs(x[1]);
F_PROFILE(f,thread,position) = wallspeed*(((6/(finalheight*finalheight))*((1/2)-(height/finalheight))*((y*y)-(finalheight*y)))-(y/finalheight)+1);

ekakavand February 22, 2010 16:17

profile in the velocity inlet

did you solve your problem,
i have this problem,too.


Goldsstean February 23, 2010 03:01


There is problem in your geometry creation.

Remember the velocity profile given for pipe, y= something something...

for e.g the pipe is of diameter 1m on y axis. you should construct it as (y=+0.5 and y=-0.5 and centre of pipe should be at "zero")

either you can make changes in udf but i feel that is tidious(not that much).


ekakavand February 24, 2010 05:43

hi Goldsstean

thanks for your attention
it's a bit odd, my case is a canal and i want to make wave in that. 'y' in my case is calculate from the bottom of canal , is different with pipe,ya?
do you try yoursef?
i try your idea....


Goldsstean February 24, 2010 05:48

Could you please explain your problem in detail.

ekakavand February 24, 2010 08:23

i model a canal with 20 m lenght and 15 m height in 2d fluent.
i wanna generate wave in canal and i hook a udf file that velocity time varing was defined in it for x and y direction. wave is generated correctly but velocity profile plot is not correct and do not match with velocity countor. it seems velocity countor is right and match with theory but profile is wrong.

i set velocity inlet in the left border of canal. and in plot menu >xy plot> i write a file of velocity in this boundary. is my way right or not?

thanks in advance

saran15 February 10, 2012 06:06

how do give parabolic inlet velocity
how do give parabolic inlet velocity profile for supersonic nozzle

maryamgh February 13, 2012 05:22

udf for velocity profile
dear all, i am new in fluent simulation. I write a udf file to define a terrain for my case. I use log law for velocity but I face to this massage: " number error floatingpoint error" .
would you please help me.:(

this is my udf file:
#include "udf.h"
real x[ND_ND];
real y;
face_t f;
y = x[1];
F_PROFILE(f,thread,position) = 5*log(y/0.4)/log(10/0.4);

student00 February 14, 2012 02:50

UDF for density variation
Please help me in making a UDF for following condition=

Variable density was defined in the liquid state as
q = ql/[b(T - Tl) + 1] for 30C < T < 100 C, where q =
760 kg/m3, Tl = 30 C, and b = 0.0005 , with linearly
varying density in the ‘‘mushy” state, from 870 kg/m3
at 28 C to 760 kg/m3 at 30 C.

Mahboobe365 June 21, 2013 14:42

Hi ekakavand,

In fluent if you use Grid or MEsh/ reorder domain/zones, it may help.

Ravindra123 June 24, 2013 06:10

Do u get the solution to your problem? I am also getting the same problem but in giving the transient temperature profile.
Any help would be appreciated.

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