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-   -   [boundary condition] logarithmic velocity profile (https://www.cfd-online.com/Forums/fluent/63748-boundary-condition-logarithmic-velocity-profile.html)

 cfdworker April 17, 2009 16:14

[boundary condition] logarithmic velocity profile

Hello, I have a problem that involves boundary condition in fluent. My boundary condition is a logarithmic velocity profile, that enters in the domain, and I don’t know how to do this in fluent. With velocity inlet I can create a regular velocity profile, but I can’t create a logarithmic velocity profile in boundary condition. So I wonder if anyone can tell me how I define a logarithmic velocity profile in boundary condition with fluent.

Thanks and sorry for my bad English

 redlemon April 17, 2009 17:40

define a profile file and call the profile in the bc file or for more flexibility use a udf for spatial variation definition using log relationship. see udf guide and define profile macro for example.

 cfdworker April 17, 2009 23:36

Hello, thanks for the answer. I tried to make an udf file, like you suggested, that defines the logarithmic profile, but when I interpreted or compiled the file, fluent report an error and can’t read the file. I wonder if the udf file I make is wrong. My udf is this file:

#include "udf.h"

DEFINE_PROFILE(inlet_x_velocity, thread, position)
{
real x[ND_ND];
real y;
face_t f;

begin_f_loop(f, thread)
{
F_CENTROID(x,f,thread);
y = x[1];
F_PROFILE(f, thread, position) = 3.*log(y/((10.)^(-2.)))/log(10./((10.)^(-2.)));
}
end_f_loop(f, thread)
}

My domain is 3d and my simulation consists in analyze the wind in a terrain. So I ask anyone if can tell me what is wrong with my udf file.

I would appreciate any suggestions.

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