# [boundary condition] logarithmic velocity profile

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 April 17, 2009, 17:14 [boundary condition] logarithmic velocity profile #1 New Member   Join Date: Apr 2009 Posts: 14 Rep Power: 15 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 Last edited by cfdworker; April 17, 2009 at 18:33.

 April 17, 2009, 18:40 #2 New Member   mark Join Date: Apr 2009 Posts: 5 Rep Power: 15 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.

 April 18, 2009, 00:36 #3 New Member   Join Date: Apr 2009 Posts: 14 Rep Power: 15 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.