# Velocity profile UDF

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 May 8, 2012, 18:29 Velocity profile UDF #1 Member   Join Date: Jan 2011 Posts: 45 Rep Power: 15 Hi, I'm trying to create a tranverse velocity profile UDF to use it as velocity inlet boundary condition to simulate flow in a water tank. The UDF is as follows: ######################################## DEFINE_PROFILE(Velocity_Profile_Z, thread, index) { real x[ND_ND]; /* this will hold the position vector */ real z; face_t f; begin_f_loop(f, thread) /* loops over all faces in the thread passed in the DEFINE macro argument */ { F_CENTROID(x,f,thread); z = x[1]; if (z < 0) z = z*(-1); else F_PROFILE(f, thread, index) = 1*pow((z/(12.8)),0.142857); } end_f_loop(f, thread) } ############################################ When I run the simulation, once it converges I plot a XY Plot, see attached figure . In my case the Z-axis represents the abscissa and the velocity magnitude the ordinate. The plot shows that even do the function represents the desire velocity profile, there is almost none velocity magnitude variation!!! Does anyone have an idea of why is that happening?? Thanks in advance. [/URL]

 May 9, 2012, 04:11 #2 Member   Daniel Tanner Join Date: Apr 2009 Posts: 54 Rep Power: 18 You have set z = x[1]. This is the y direction on your mesh, is that correct? The x vector is given by: (x[0], x[1], x[2]) which is equivalent to (x,y,z). Worth checking this.

 May 10, 2012, 13:03 #3 Member   Join Date: Jan 2011 Posts: 45 Rep Power: 15 Thanks Daniel!! That was the problem!!!!!