Hello, I was experiencing a hard time to track a particle in an unsteady flow. I used a simple UDF to get the current position of a particle and wrote it to a text file. However, when I compared the postion in the file and the position reported by "display"->"particle tracks"->"current positions", they are different--although the difference is small. I am using 6.2.

Also, how is the "solve"->"particle history" working in Fluent menu? The help file really wasnt helpful for me.

Thanks a lot!

P.S. the code:

#include "udf.h" #include "dpm.h" //#include "stdio.h"

/* update the user scalar variables */

DEFINE_DPM_SCALAR_UPDATE(follow_particle, cell, thread, initialize, p) {

FILE *pf;

pf = fopen ("oneparticle.txt", "a+t");

fprintf (pf, "%f, %f, %f, %f, %f, %f, %f\n", P_TIME(p), P_POS(p)[0], P_POS(p)[1], P_POS(p)[2],P_VEL(p)[0], P_VEL(p)[1], P_VEL(p)[2]);

fclose(pf);

}

Another question is that: the file could not be created unless I run several iterations under steady state first. I am desperate on this... thanks.

[Hanz]

I can see it has been a while since your post.

However, I am experiencing a similar problem with data errors.

I want to simply find the relative velocity between the particles in a cell.

I know that the calculated value I have should be roughly zero, however my calculated value is 0.18m/s which is higher than it should be.

Could this be to do with my variable definitions. I use double. How do I know whether to use double or float?