# problem with udf

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 September 8, 2011, 08:39 problem with udf #1 New Member   Harpreet Join Date: May 2011 Posts: 21 Rep Power: 8 Sponsored Links hello, pls help i am trying to vary the inlet velocity profile for which i have made a following udf #include "udf.h" DEFINE_PROFILE(variable_velocity,t,i) { real x[ND_ND]; real y; face_t f; begin_f_loop(f,t) { F_CENTROID(x,f,t); y=x[1]; F_PROFILE(f,t,i)=7.36+0.368*y; } end_f_loop(f,t) } but the problem with it is that it is giving a constant velocity at the inlet that is 7.36. I think that probably it is not taking the coordinate into the equation. pls help me. its urgent

 September 9, 2011, 09:10 #2 Member     Laurent B Join Date: Jun 2009 Location: Lille, FRANCE Posts: 70 Rep Power: 10 Hi, You can add after F_CENTROID line : printf("x-coord = %f y-coord = %f", x[0], x[1]);

 September 9, 2011, 09:46 #3 Senior Member   Mohammad Join Date: Feb 2010 Location: Shiraz, Iran Posts: 109 Rep Power: 9 hi, check if you are hooking udf in correct boundary. does the boundary have variable y-coordinate? your case is 2d or 3d?

 September 11, 2011, 00:45 #4 New Member   Harpreet Join Date: May 2011 Posts: 21 Rep Power: 8 my case is 2d, and i am hooking it in velocity inlet boundary condition.Another thing i noticed that, if i scale my in unit of 'm', the variation in velocity is obserable, but the same is not the case when it is scaled in 'mm' units.

 September 12, 2011, 07:06 #5 New Member   Join Date: Mar 2009 Posts: 15 Rep Power: 10 the UDF takes units of your mesh scaled in Fluent interface, just check in SCALE panel. Further, check whether your position in UDF is y position or x position. If it is x, you have to write x = x[0]. If it is y, you write y=x[1]

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