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Old   August 13, 2008, 19:11
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/* This function initializes my domain on the left side with species 0 at 300K and species 1 at 600K on the right side. domain is 1 meter long */

#include "udf.h"

DEFINE_INIT(my_init_function,d) { cell_t c; Thread *t; real xc[ND_ND];

thread_loop_c(t,d) {

begin_c_loop_all (c,t)



if (xc[0] < 0.5)


C_T(c,t) = 300.;

C_YI(c,t,0) = 0.;




C_T(c,t) = 600.;

C_YI(c,t,0) = 1.;



end_c_loop_all(c,t) } }

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Old   August 13, 2008, 19:16
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The above UDF compiles and runs when hooked. The temperature on the left is 300K and the temp on the right is 600K. Species 0 is on the left and Species 1 is on the right.

However, when i zoom into the walls on the right side, the wall nodes appear to be initialized with Species 0.

I think that I need to add an f_loop to initialize nodes on the wall but the temperature loop seemed to work fine. Any ideas?

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Old   August 14, 2008, 02:28
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Assign the species mass fraction in the wall boundary conditions. By default the mass fraction of all the species will be zero. You do not need a UDF to assign the same on the walls. Regards,

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Old   August 14, 2008, 18:34
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Thanks for the response.

My wall boundary is set to: Zero Diffusive Flux for species and 0 Heat Flux for Temp. So, my wall species and Temp is allowed to float based on what happens in the interior.

When I initialize the domain to one temp and species without the UDF using solve/initialize I see that all interior nodes and wall nodes are at the initialized species and temperature.

When I initialize the domain using my UDF I find that only the interior nodes are properly initialized (because I have only looped on cell centroids).

Since I don't want to specify species or temp as a boundary condition, I believe that I must do something extra with my UDF to initialize the remaining part of my domain that my begin_c_loop missed.

Thanks again.

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Old   January 4, 2019, 06:58
Default UDF not initialzing species mass fraction
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Kedar G. Bhide
Join Date: Apr 2016
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I've UDF that defines species mass fraction in the form of a profile.

#include "udf.h"
2 DEFINE_INIT(my_init_func, d)
3 {
4 cell_t c;
5 Thread *t;
6 real xc[ND_ND];
7 real x;
8 real phiphi;
9 real l1;
10 real l2;
11 real loc;
12 real dl;
13 real k;
14 int i;
15 Material *m, *sp;
16 printf("\n end of variables declarations");
17 l1=0.0;
18 l2=0.004;
19 loc=0.0;
20 k=2500.0;
21 thread_loop_c(t,d)
22 {
23 begin_c_loop_all(c,t)
24 {
25 C_CENTROID(xc,c,t);
26 loc=xc[0];
27 phiphi=((1.0/(1.0+exp(-2*k*(loc-l1))))-(1.0/(1.0+exp(-2.0*k*(loc-l2)))));
28 if(xc[0] < 0.002)
29 {
30 phiphi=1.0;
31 }
33 mixture_species_loop(m,sp,i)
34 {
35 printf("\n %d",i);
36 }*/
37 C_T(c,t)=300.0+phiphi*1360.0;
38 C_YI(c,t,0)= 1.0*phiphi;
39 C_YI(c,t,1)= 1.0*(1-phiphi);
40 C_YI(c,t,2)= 0.0;
41 C_YI(c,t,4)= 0.0;
42 C_YI(c,t,4)= 0.0;
43 C_YI(c,t,5)= 0.0;
44 }
45 end_c_loop_all (c,t)

It gets hooked and executes without showing any error. However, only temperature gets initialized as per the equation. Mass fractions continue to remain zero.
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