Interpreted UDF
 

hi

i am trying to use UDF for two different temperature boundary conditons varying with time. one is at the inlet and other one is for ambient air. i have two different equations guiding the temperature. when i compile the udf i get only one udf while defining the boundary conditions. the last one compiled overlaps the previous one, so i cannot define two different boundary condition using the UDF. i used different name while defining the macros, but it didnt work.

i would appreciate any help and suggestions

thank you bikash

Re: Interpreted UDF
 

Yo have to use a multiple UDF. Take the two codes and put in the same file, after compiled.

When you compiled the file, you will have two UDF for your case.

Re: Interpreted UDF
 

hi abraham,

well thanks for your help. can you give me more details about how to put two codes in the same file? i really dont know how to put two codes in the same file and compile. i really appreciate your help

thank you bikash

Re: Interpreted UDF
 

#include "udf.h"

define_profile(temp1...) { } define_profile(temp2...) { }

Then save the file and compile the UDF. ( interrupted).

Mahesh

Re: Interpreted UDF
 

The following code is of the fluent user´s manual

Example 2 In the following example, DEFINE PROFILE is used to generate pro les for the x velocity, turbulent kinetic energy, and dissipation rate, respectively, for a 2D fully-developed duct flow. Three separate UDFs named x velocity, k profile, and dissip profile are de ned. These functions are concatenated in a single C source le which can be executed as interpreted or compiled in FLUENT. The 1/7th power law is used to specify the x velocity component: vx = vx;free y  1=7 A fully-developed pro le occurs when  is one-half the duct height. In this example, the mean x velocity is prescribed and the peak (free-stream) velocity is determined by averaging across the channel. The turbulent kinetic energy is assumed to vary linearly from a near-wall value of knw = u2  qC to a free-stream value of kinf = 0:002u2 free The dissipation rate is given by  = C3=4  (k3=2) ` where the mixing length ` is the minimum of y and 0.085. ( is the von Karman constant = 0.41.) The friction velocity and wall shear take the forms u = qw= w = fu2 free 2 The friction factor is estimated from the Blasius equation: f = 0:045 ufree  !?1=4 4-28 c Fluent Inc. December 3, 2001 4.3 Model-Speci c DEFINE Macros /************************************************** ********************/ /* Concatenated UDFs for fully-developed turbulent inlet profiles */ /************************************************** ********************/ #include "udf.h" #define YMIN 0.0 /* constants */ #define YMAX 0.4064 #define UMEAN 1.0 #define B 1./7. #define DELOVRH 0.5 #define VISC 1.7894e-05 #define CMU 0.09 #define VKC 0.41 /* profile for x-velocity */ DEFINE_PROFILE(x_velocity, t, i) { real y, del, h, x[ND_ND], ufree; /* variable declarations */ face_t f; h = YMAX - YMIN; del = DELOVRH*h; ufree = UMEAN*(B+1.); begin_f_loop(f, t) { F_CENTROID(x,f,t); y = x[1]; if (y <= del) F_PROFILE(f,t,i) = ufree*pow(y/del,B); else F_PROFILE(f,t,i) = ufree*pow((h-y)/del,B); } end_f_loop(f, t) } /* profile for kinetic energy */ c Fluent Inc. December 3, 2001 4-29 DEFINE Macros DEFINE_PROFILE(k_profile, t, i) { real y, del, h, ufree, x[ND_ND]; real ff, utau, knw, kinf; face_t f; h = YMAX - YMIN; del = DELOVRH*h; ufree = UMEAN*(B+1.); ff = 0.045/pow(ufree*del/VISC,0.25); utau=sqrt(ff*pow(ufree,2.)/2.0); knw=pow(utau,2.)/sqrt(CMU); kinf=0.002*pow(ufree,2.); begin_f_loop(f, t) { F_CENTROID(x,f,t); y=x[1]; if (y <= del) F_PROFILE(f,t,i)=knw+y/del*(kinf-knw); else F_PROFILE(f,t,i)=knw+(h-y)/del*(kinf-knw); } end_f_loop(f, t) } /* profile for dissipation rate */ DEFINE_PROFILE(dissip_profile, t, i) { real y, x[ND_ND], del, h, ufree; real ff, utau, knw, kinf; real mix, kay; face_t f; h = YMAX - YMIN; del = DELOVRH*h; ufree = UMEAN*(B+1.); ff = 0.045/pow(ufree*del/VISC,0.25); utau=sqrt(ff*pow(ufree,2.)/2.0); knw=pow(utau,2.)/sqrt(CMU); 4-30 c Fluent Inc. December 3, 2001 4.3 Model-Speci c DEFINE Macros kinf=0.002*pow(ufree,2.); begin_f_loop(f, t) { F_CENTROID(x,f,t); y=x[1]; if (y <= del) kay=knw+y/del*(kinf-knw); else kay=knw+(h-y)/del*(kinf-knw); if (VKC*y < 0.085*del) mix = VKC*y; else mix = 0.085*del; F_PROFILE(f,t,i)=pow(CMU,0.75)*pow(kay,1.5)/mix; } end_f_loop(f,t) } c Fluent Inc. December 3, 2001 4-31

Re: Interpreted UDF better
 

Example 2

/**************************************************/

/* Concatenated UDFs for fully-developed turbulent inlet profiles */ /********************************************/

#include "udf.h"

#define YMIN 0.0 /* constants */

#define YMAX 0.4064

#define UMEAN 1.0

#define B 1./7.

#define DELOVRH 0.5

#define VISC 1.7894e-05

#define CMU 0.09

#define VKC 0.41

/* profile for x-velocity */

DEFINE_PROFILE(x_velocity, t, i)

{

real y, del, h, x[ND_ND], ufree; /* variable declarations */

face_t f;

h = YMAX - YMIN;

del = DELOVRH*h;

ufree = UMEAN*(B+1.);

begin_f_loop(f, t)

{

F_CENTROID(x,f,t);

y = x[1];

if (y <= del)

F_PROFILE(f,t,i) = ufree*pow(y/del,B);

else

F_PROFILE(f,t,i) = ufree*pow((h-y)/del,B);

}

end_f_loop(f, t)

}

/* profile for kinetic energy */

DEFINE_PROFILE(k_profile, t, i)

{

real y, del, h, ufree, x[ND_ND];

real ff, utau, knw, kinf;

face_t f;

h = YMAX - YMIN;

del = DELOVRH*h;

ufree = UMEAN*(B+1.);

ff = 0.045/pow(ufree*del/VISC,0.25);

utau=sqrt(ff*pow(ufree,2.)/2.0);

knw=pow(utau,2.)/sqrt(CMU);

kinf=0.002*pow(ufree,2.);

begin_f_loop(f, t)

{

F_CENTROID(x,f,t);

y=x[1];

if (y <= del)

F_PROFILE(f,t,i)=knw+y/del*(kinf-knw);

else

F_PROFILE(f,t,i)=knw+(h-y)/del*(kinf-knw);

}

end_f_loop(f, t)

}

/* profile for dissipation rate */

DEFINE_PROFILE(dissip_profile, t, i)

{

real y, x[ND_ND], del, h, ufree;

real ff, utau, knw, kinf;

real mix, kay;

face_t f;

h = YMAX - YMIN;

del = DELOVRH*h;

ufree = UMEAN*(B+1.);

ff = 0.045/pow(ufree*del/VISC,0.25);

utau=sqrt(ff*pow(ufree,2.)/2.0);

knw=pow(utau,2.)/sqrt(CMU);

kinf=0.002*pow(ufree,2.);

begin_f_loop(f, t)

{

F_CENTROID(x,f,t);

y=x[1];

if (y <= del)

kay=knw+y/del*(kinf-knw);

else

kay=knw+(h-y)/del*(kinf-knw);

if (VKC*y < 0.085*del)

mix = VKC*y;

else

mix = 0.085*del;

F_PROFILE(f,t,i)=pow(CMU,0.75)*pow(kay,1.5)/mix;

}

end_f_loop(f,t)

}

Re: Interpreted UDF better
 

hi

thanks a lot for your help. i will try to use the ideas. i'll get back to you guys if i get any trouble.

i really appreciate your help abraham.

Re: Interpreted UDF better
 

hi abraham,

i followed the example that you gave me for concatenated udfs.

i get syntax error on the line when i add the second udf in the same code file.

i checked everything but its not working, it works if i take the second udf out and just compile single udf.

may be you can suggest me something.

i respect your time and greatly appreciate your help

thankyou

bikash

-------------------------------------------------------------------------------------------------------------------------------------- #include "udf.h"

DEFINE_PROFILE(unsteady_velocity1, thread, position) { face_t f;

begin_f_loop(f, thread)

{

real t = RP_Get_Real("flow-time");

F_PROFILE(f, thread, position) = 20. + 5.0*sin(10.*t);

} end_f_loop(f, thread) }*****************

DEFINE_PROFILE(unsteady_velocity2, thread, position) { face_t f;

begin_f_loop(f, thread)

{

real t = RP_Get_Real("flow-time");

F_PROFILE(f, thread, position) = 20. + 5.0*sin(10.*t);

} end_f_loop(f, thread) }

My udf is pretty much similar to this, i followed the above syntax. i couldnt get access to my program now, cause im in the library. i get error on that line *********************

Re: Interpreted UDF better
 

hi abraham

it worked the way you told me.

thanks a lot

bikash

Delovrh meaning
 

Hi all,

Could you please let me know, what does DELOVRH means. and how they are doing del= DELOVRH*h. in this profile generation, can i use log law instead of power law? is it makes any difference.thanks

Its urgent
 

hi can you please elaborate the meaning of YMIN,YMAX,UMEAN,B,DELOVRH,CMU,VKC.PLEASE HELP ME ANYBODY.