problem with udf

Harpreet · September 8, 2011, 08:39

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

laurentb · September 9, 2011, 09:10

Hi,
You can add after F_CENTROID line :
printf("x-coord = %f y-coord = %f", x[0], x[1]);

m2montazari · September 9, 2011, 09:46

hi,
check if you are hooking udf in correct boundary. does the boundary have variable y-coordinate?
your case is 2d or 3d?

Harpreet · September 11, 2011, 00:45

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.

bohis · September 12, 2011, 07:06

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]

September 8, 2011, 08:39	problem with udf	#1
Harpreet New Member Harpreet Join Date: May 2011 Posts: 21 Rep Power: 14	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

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September 9, 2011, 09:10		#2
laurentb Member Laurent B Join Date: Jun 2009 Location: Lille, FRANCE Posts: 70 Rep Power: 16	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
m2montazari Senior Member Mohammad Join Date: Feb 2010 Location: Shiraz, Iran Posts: 108 Rep Power: 16	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
Harpreet New Member Harpreet Join Date: May 2011 Posts: 21 Rep Power: 14	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
bohis New Member Join Date: Mar 2009 Posts: 15 Rep Power: 17	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]