# Velocity boundary condtion UDF help

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 October 8, 2012, 17:31 Velocity boundary condtion UDF help #1 Member   Join Date: Sep 2012 Location: FL Posts: 76 Rep Power: 4 I have a rectangular inlet (2x1-in X and Z)for a 3 D problem where I want to give a UDF for y velocity (-ve direction). The centre of the of the rectangular inlet is at (-2.5,2,8). The maximum velocity is 10. The profile is parabolic in x and z directon. I have written a UDF. But the velocity comes out to be >100. I don't know where I'm I doing wrong. /************************************************** ***********************/ /* udf- velocity profile boundary condition */ /************************************************** ***********************/ #include "udf.h" DEFINE_PROFILE(inlet_y_velocity, thread, index) { real p[ND_ND]; real x,z; face_t f; begin_f_loop(f, thread) { F_CENTROID(p,f,thread); x = p[1]; z= p[1]; F_PROFILE(f, thread, index) = (10-10*((x+2.5)*(x+2.5))-10*(((z-2)/0.5)*((z-2)/0.5))); } end_f_loop(f, thread) }

 October 9, 2012, 04:38 #2 Senior Member     Alex Join Date: Jun 2012 Location: Germany Posts: 1,104 Rep Power: 19 The x, y and z-values of the face centroids are stored in p[0], p[1] and p[2], respectively. So first of all you should change the line "x=p[1];" to "x=p[0]" and the line "z=p[1];" to "x=p[2]" Didn't check the rest of your formula, so there could still be some more errors.

 October 9, 2012, 15:27 #3 Member   Join Date: Sep 2012 Location: FL Posts: 76 Rep Power: 4 Thanks man.I totally forgot about that. I am getting proper results now. Also, I did miss negative sign in the formula.

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